REPORT
657
Seabed and overburden
integrity monitoring for
offshore CO2 storage
OCTOBER
2023
Acknowledgements
This guideline was written by the IOGP Environment Committee, in collaboration
with the Carbon Capture, Transportation, and Storage (CCTS) Committee,
Geomatics Committee, and Metocean Committee.
Front cover photography used with permission courtesy of
© Vismar UK/Shutterstock and © Red ivory/Shutterstock
About
The Report provides a set of common industry good practices for demonstrating
the ongoing integrity of an offshore CO2 storage project and to provide assurance
to the operator(s), local regulatory bodies, or public stakeholders that the
injected CO2 remains in the storage unit over the full project lifecycle. Using
these guidelines, the operator should be able to demonstrate that, in the case of
anomalies or unexpected leakage detected in the overburden and/or at seabed,
the necessary mitigation measures are in place to identify the issue promptly
and thus reduce the impact of the leak to a minimum level. The scope and focus
of this Report are on the marine environment, seabed, and shallow overburden,
limited to the units above the storage complex.
Based on recent research results and industrial projects, this Report proposes
a full set of steps and approaches to be used along with advice on the specific
available (or emerging) tools and techniques that can be used to provide industry
with the most appropriate methods for defining pre-project start-up baseline
conditions and the subsequent ongoing shallow focused monitoring plans during
a project’s operational life span and after its decommissioning.
Feedback
IOGP welcomes feedback on our reports: publications@iogp.org
Disclaimer
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liability is hereby excluded. Consequently, such use is at the recipient’s own risk on the basis that any use by the recipient constitutes agreement to the terms
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Please note that this publication is provided for informational purposes and adoption of any of its recommendations is at the discretion of the user. Except
as explicitly stated otherwise, this publication must not be considered as a substitute for government policies or decisions or reference to the relevant
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REPORT
657
Seabed and overburden
integrity monitoring for
offshore CO2 storage
Revision history
VERSION
DATE
AMENDMENTS
1.0
October 2023
First release
OCTOBER
2023
Seabed and overburden integrity monitoring for offshore CO2 storage
Contents
Introduction
5
1 Measurement, Monitoring, and Verification (MMV) concepts for CO2 storage
6
1.1 Context and concepts
6
1.1.1 The purpose of MMV
6
1.1.2 Deep-focused versus shallow-focused monitoring
6
1.1.3 MMV philosophy
7
1.1.4 MMV design
7
1.1.5 The bowtie risk assessment framework
8
1.1.6 Preventive monitoring
10
1.1.7 Contingency monitoring
10
2 Baseline and monitoring guidance
11
2.1 Data management
11
2.1.1 Data management justification
11
2.1.2 Data manager and owner roles
12
2.1.3 Data updates
12
2.1.4 Data integration
12
2.1.5 Building a GIS
13
2.1.6 Seabed and shallow overburden data management
15
2.1.7 Managing geodetic integrity
15
2.1.9 Use of existing datasets
18
2.2 Developing the near-surface MMV plan
21
2.2.1 The near-surface MMV - a key element of the overall MMV programme
21
2.2.2 Summary of typical datasets required
22
2.2.3 Ways of handling long-term variability/continuity (drifting baseline)
22
2.2.4 Identification and definition of anomalous events
23
2.2.5 Requirements for verification and attribution
24
2.2.6 Routine surveys versus targeted surveys
25
2.2.7 Anomaly response plans
26
3 Technical notes
28
3.1 Baseline methods
28
3.1.1 Geophysics
28
3.1.2 Environment
29
3.1.3 Metocean and geochemical data requirements
29
4
Seabed and overburden integrity monitoring for offshore CO2 storage
3.2 Monitoring methods
34
3.2.1 Acquisition platforms
34
3.2.2 Acquisition sensors (geophysics, hydroacoustic, geochemistry, biological)
38
3.2.3 Example missions and surveys
42
3.2.4 Data management, processing
46
3.3 Value of information
47
3.4 Workflow decision diagram (to help operators make appropriate choices)
47
Appendix A: Review of regulatory frameworks and standards relevant to seabed and
overburden integrity
50
A.1. International Regulations
50
A.1.1 The London Protocol
50
A.1.2 The OSPAR convention:
50
A.2 European Regulations
51
A.2.1 Directive 2009/31/EC (CCS Directive)
51
A.2.2 Directive 85/337/EEC (EIA Directive)
52
A.2.3 Directive 92/43/EEC (Habitats Directive)
52
A.2.4 Directive 2003/87/EC (ETS Directive)
52
A.2.5 Directive 2004/35 (Environmental Liability Directive)
53
A.2.6 Directive 2008/56/EC (Marine Strategy Framework Directive)
53
A.2.8 Regulatory context in the UK
53
A.2.7 Regulatory context in Netherlands
54
A.2.8 Regulatory context in Norway
54
A.3. Examples of regulations from other countries
60
A.3.1 Australian regulations and guidelines
60
A.3.2 Japanese regulations
60
A.4 Standards and recommended practices
63
A.4.1 ISO 27924:2017 Carbon dioxide capture, transportation, and geological storage — Geological storage
63
A.4.2 ISO/FDIS 19901-10 Marine Geophysical Investigations and ISO/FDIS 19901-08 Marine Soil Investigations
63
A.4.3 DNV-RP-J203: Geological Storage of Carbon Dioxide
63
A.4.4 DNVGL-RP-F104: Design and operation of carbon dioxide pipelines
63
Appendix B: Case studies
64
References
66
5
Seabed and overburden integrity monitoring for offshore CO
CO22 storage
Introduction
This Report provides a set of good practices for demonstrating the ongoing integrity of an
offshore CO2 storage project and to provide assurance to operators, regulatory bodies, and public
stakeholders that the injected CO2 remains in the storage unit as intended. The CO2 should remain
underground for at least 1,000 years. With application of these guidelines, operating companies
should be able to demonstrate that, in the case of anomalies or unexpected leakage detected in the
shallow overburden (geological interval between the CO2 storage cap-rock and the seabed) and/
or at seabed, the necessary mitigation measures are in place to identify the issue promptly and
thus reduce the impact of the leak to a minimum level, confined to the shallow overburden, and
according to the regulation requirements. The scope and focus of this guidelines are on the marine
environment, seabed, and shallow overburden, limited to the units above the storage complex.
Based on recent research and development results and industrial projects, the Report proposes a
full set of steps and approaches to be used along with advice on the specific available (or emerging)
tools and techniques that can be used to provide industry with the most appropriate methods for
defining pre-project start-up baseline conditions and the subsequent ongoing shallow focused
monitoring plans during a project’s operational life span and after its decommissioning.
6
CO2 storage
Seabed and overburden integrity monitoring for offshore CO2
1
Measurement, Monitoring, and
Verification (MMV) concepts for CO2 storage
1.1
Context and concepts
Geologic CO2 storage is a safe, reliable, and economically feasible technology to unlock
the significant potential of offshore CO2 storage for effective climate change mitigation.
To achieve this, a set of agreements need to be developed between operators, regulators,
and a range of public stakeholders. Meeting legal requirements and demonstrating safe
storage through a risk-based monitoring approach are essential. The purpose of a riskbased Measurement, Monitoring, and Verification (MMV) plan is to verify and ensure
conformance and containment of the injected CO2. It is based on a systematic site-specific
storage containment risk assessment using, for example, the bowtie method and leakage
scenarios. Other drivers that influence MMV are country-specific regulatory requirements
and stakeholder concerns.
For more information, see IOGP Report 652 - Recommended practices for measurement,
monitoring, and verification plans associated with geologic storage of carbon dioxide.
1.1.1 The purpose of MMV
The main goals of a MMV plan can be summarized using the terms containment,
conformance, and confidence.
• Containment: provide evidence for the effectiveness of containment system and
to address to stakeholder concerns about potential for leakage or to trigger early
intervention if needed.
• Conformance: demonstrate that the storage is progressing as expected and the longterm behaviour of the CO2 is understood, typically by showing that forward models are
consistent with monitoring data.
• Confidence: provide data for emission accounting, to support transfer of long-term
responsibilities to the relevant authorities and to maintain license to operate (LtO).
1.1.2 Deep-focused versus shallow-focused monitoring
To be effective, MMV plan should cover the area of influence where there is potential for
impacts due to CO2 storage, including the displacement of formation fluids (different
jurisdictions may call this an area of review or area of interest). Further, the MMV
programme should assess a comprehensive spatial volume (geosphere, hydrosphere,
biosphere, and the environment above a site) and should cover the pre-injection, injection,
post-injection, and post-closure phases. The focus of this Report is on seabed and shallow
overburden integrity monitoring for offshore CO2 storage projects and therefore a clear
distinction between deep- and shallow-focused monitoring is made:
• Deep-focused monitoring should identify unexpected migration of CO2 out of
the primary storage units (geologic structure), into the overburden and possible
movement out of the storage complex leading to a surface leakage. This containment
monitoring should be considered an early warning system for leak detection. Refer to
7
Seabed and overburden integrity monitoring for offshore CO
CO22 storage
IOGP Report 652 - Recommended practices for measurement, monitoring, and
verification plans associated with geologic storage of carbon dioxide for further details
regarding MMV within geologic structures.
• Shallow-focused monitoring aims to detect CO2 migration in the shallow subsurface
(including the shallow overburden above the caprock) and possible leakage to surface
or seabed. The shallow focused monitoring should be capable of detecting and
quantifying possible leakage at the surface that is likely to pose a health and safety
threat or environmental impact.
Shallow-focused monitoring (for containment and contingency) relies upon near surface
geophysical, geotechnical, and environmental monitoring technologies generally developed
and implemented by marine geoscientists, oceanographers, and environmental scientists.
An important issue connected with shallow-focused monitoring is differentiating possible
CO2 leakage from the storage site from the natural variations in CO2 concentrations in the
shallow subsurface or surface environments. Anomaly detection and assessment is usually
needed before possible leakage can be confirmed.
A thorough baseline understanding of the geological and oceanographic parameters will
need to be established, firstly to detect anomalous events and, secondly, to determine their
root cause. For example, natural fluid fluxes from the seabed are not uncommon and may
be incorrectly attributed to injection activities.
1.1.3 MMV philosophy
A base case MMV plan should be risk-based (both technical and non-technical risks) and
should satisfy regulatory and potentially stakeholder requirements. Leakage scenario
studies are recommended to inform acquisition of adequate baseline data to enable
reactive contingency monitoring if loss of containment is suspected.
A responsible operator of an offshore CO2 storage project will also wish to provide careful
definition of the baseline conditions in the shallow overburden and seabed before project
start-up, as a basis for demonstration of the ongoing integrity of the project over its
lifespan, and eventually to demonstrate the project has no adverse implications for the
marine or atmospheric environment. Expected changes to the marine environment and
seabed due to other anthropogenic factors should also be considered.
1.1.4 MMV design
The MMV design process works within this risk management framework and supports the
storage (reservoir) screening process selection by evaluating site-specific storage risks
(using the bowtie method, see Section 1.1.5) before proceeding to implement additional
safeguards supported by monitoring in the following order:
1)
Assess site-specific storage risks: establish definitions for loss of conformance and
loss of containment. Identify potential threats and consequences associated with
these risk events.
2)
Characterize geological safeguards: identify and appraise the integrity and quality of
the geological seals.
8
Seabed and overburden integrity monitoring for offshore CO2 storage
3)
Select initial safeguards: identify and assess the engineering concept selections that
provide safeguards against unexpected loss of well integrity.
4)
Evaluate these initial safeguards: evaluate the expected efficacy of these initial
safeguards in relation to the identified conformance and containment threats, and
their potential consequences.
5)
Establish monitoring requirements: define monitoring tasks to verify the performance
of these initial safeguards and, if necessary, trigger timely control measures.
6)
Select monitoring technologies: select monitoring technologies according to a costbenefit ranking where benefits are judged according to how effective each technology
is at each task.
7)
Establish performance targets: evaluate the expected monitoring capabilities.
8)
Identify contingency monitoring technologies: develop alternative monitoring plans
should technologies underperform, or alerts require additional information to assess
containment risks.
9)
Identify control measures: design interventions to reduce the likelihood or the
consequence of any unexpected loss of conformance and containment. These include
operational controls and updates to model-based predictions.
1.1.5 The bowtie risk assessment framework
The bowtie method provides a framework for a systematic risk assessment of events
with the potential to affect CO2 storage performance1,2. The bowtie shows the relationship
between the five key elements (Figure 1) that describe how a risk might arise and how
safeguards can provide effective protection against the risk and its
associated consequences.
• Top event: this is the unwanted event, placed in the centre of the bowtie. For example,
this could be the movement of injected CO2 outside the geologic storage site.
• Threats: these are the possible mechanisms that can lead to the top event. For
example, the presence of a permeable fault or fracture system, stress of injection, or
poorly plugged abandoned wells.
• Consequences: these are the possible adverse outcomes due to the occurrence of the
top event such as negative impact on the environment due to CO2 or associated
brine emission.
• Preventative safeguards: these decrease the likelihood of a threat leading to the top
event. For example, multiple geologic seals reduce the likelihood of CO2 ever reaching
the surface.
• Corrective safeguards: these decrease the likelihood of significant consequences due
to a top event. For example, the presence of additional permeable formation below
the top seal of a geologic storage site provides an alternative secondary storage.
1
2
Dean M and Tucker O, 2017
Bourne S, Crouch S, and Smith M, 2014
9
Seabed and overburden integrity monitoring for offshore CO2 storage
Figure 1: The elements of a bowtie used for subsurface containment risk assessment
Within the context of a Measurement, Monitoring and Verification (MMV) plan, both
preventative and corrective safeguards can take two distinct forms:
Passive safeguards: These are always present from the start of operation and do not need
to be activated. There are two types of passive safeguards: Geological barriers identified
during site characterization and engineered barriers identified during engineering
concept selections.
Active safeguards: These engineered barriers may be brought into service in response
to some indication of a potential upset condition to make the site safe. Active safeguards
require three key components to operate effectively:
• A
­ sensor capable of detecting changes with enough sensitivity and reliability to
provide an early indication that some form of intervention is required.
• A
­ decision logic to interpret the sensor data and select the most appropriate form of
intervention.
• A
­ control response capable of effective intervention to ensure continuing storage
performance or to mitigate consequences.
The combination of a sensor, decision logic, and a control response is the mechanism
for the additional risk mitigation provided by the MMV plan. The monitoring requirements
follow from the set of control measures that could prevent each threat (left side of the
bowtie) or correct each consequence (right side of the bowtie) if triggered in time by
reliable monitoring.
10
Seabed and overburden integrity monitoring for offshore CO2 storage
1.1.6 Preventive monitoring
To maximize detection efficiency and to avoid both false positives and false negatives, a
thorough understanding of the marine environment is required. Understanding natural
variations is a key issue for shallow monitoring and leak detection, and baseline datasets
are an important part of the process. Studies so far have shown that CO2 concentrations
in the marine environment vary significantly on daily and seasonal timescales and vary
spatially (near-shore versus far-shore) so that establishing a baseline for anomaly
detection is itself challenging. Therefore, the use of natural and artificial tracers to enable
attribution (e.g., establish if the detected CO2 is from the storage operation) should
be assessed.
Preventative monitoring near risk features (active pockmarks, shallow faults, abandoned
wells, etc.) is recommended considering any potential leakage paths from the reservoir to
these features. Early warning signals concerning anomalies detected within the storage
unit (reservoir) are likely recorded by borehole technologies (e.g., pressure and temperature
gauges) or geophysical methods (e.g., time-lapse seismic).
1.1.7 Contingency monitoring
It is expected that the deep-focused monitoring will indicate a potential loss of containment
well in time to deploy shallow contingency monitoring. Several research and development
projects have studied such shallow contingency monitoring and benchmarked the
technologies with controlled CO2 releases resulting in guidelines for CO2 leak detection
(gas phase or dissolved phase), location, attribution, and quantification. The studies (QICS,
RISCS, ECO2, STEMM-CCS, ETI-MMV, ACT4Storage)3 have also shown that the impact of
emitted CO2 is generally limited in space and time due to rapid mixing and dissolution.
These projects have demonstrated and qualified several technologies based on nearsurface geophysics, hydro-acoustics, and bio/geochemistry. Some methods use static
seabed detection systems (landers) while others use dynamic platforms (surface vessels,
AUVs, ROVs, gliders). The technology options which are available are diverse, but likely
will require further maturation for long-term deployment, efficient data processing, and
enhanced interpretation to enable real-time decision making.
3
QICS = Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage (http://www.qics.co.uk)
RISCS = Research into Impacts and Safety in CO2 Storage, http://www.riscs-co2.eu/
ECO2 = Sub‐seabed CO2 storage: Impact on Marine Ecosystems, https://www.eco2-project.eu/
STEMM-CCS = Strategies for Environmental Monitoring of Marine Carbon Capture and Storage, https://www.stemm-ccs.eu/
ETI-MMV = Energy Technologies Institute - Measurement, Monitoring and Verification of CO2 Storage https://www.eti.co.uk/
programmes/carbon-capture-storage/measurment-modelling-and-verrfication-of-co2-storage-mmv
ACT4Storage = Acoustic and Chemical Technologies for environmental monitoring of geological carbon storage,
https://www.ngi.no/eng/Projects/ACT4storage-Technologies-for-monitoring-of-CO2-storage
11
Seabed and overburden integrity monitoring for offshore CO2 storage
2
Baseline and monitoring guidance
2.1
Data management
Technical data is a key business asset and fundamental to efficient business processes and
quality decisions. It is an integral part of an offshore CO2 storage lifecycle management,
supporting better understanding of near surface, well, and reservoir assessment, and
facility performance.
Obtaining the necessary data to optimize system performance, mitigate HSSE risk, and
meet legal and regulatory requirements requires planning and clear links to outcomes.
Given the number of data options available, a clearly defined and budgeted data
management plan is a key component of a successful MMV project.
The data management plan should be defined considering:
• Data requirements – existing and new
• Data generation, acquisition, processing, and storage requirements
• Data governance requirements - ensuring a consistent approach to data handling
• Data management requirements over life of field - including storage, retrieval, quality
control, spatial integrity, accessibility, visualization, privacy and security
• Methodologies and standards requirements for creating, accessing, and regularly
updating across diverse data tiers
• Data handling requirements at design, planning, execution, and completion stages
• Data usage and metadata requirements across multiple applications/software,
algorithms, analytics - ensuring high availability and rapid disaster recovery
• Data curation, archive and destruction in compliance with retention schedules
and guidelines
The data management plan should be an active document, updated during the project as
required, and referenced in the MMV plan, with a short summary of the data
management approach.
2.1.1 Data management justification
The CCS MMV plan should ensure that data is accessible, readily discoverable and fit
for purpose in terms of quality (completeness, correctness, consistency, currency). Data
definition owners should define the business rules by which data quality is measured and
quality tagged.
Prospective data users should be supported by fully searchable metadata, published in data
repositories, and prepared to recognized standards. Data should be accessible to the asset
team as well as business partners, customers, suppliers, regulators and other external
parties to support effective use and exchange of information and valid business decisions.
12
Seabed and overburden integrity monitoring for offshore CO2 storage
Regulatory requirements for greenhouse gas titleholders may include collection and
retention of reports, cores, cuttings, and samples that can be retrieved in compliance with
applicable legal, regulatory, and contractual obligations. This may include geophysical,
geotechnical, and geological survey reports, and all associated processing, interpretation,
survey data and reports within the greenhouse gas injection monthly report for each well in
the license area.
2.1.2 Data manager and owner roles
Dedicated, specialist MMV data acquisition and management support is strongly
recommended, to provide suitable points of contact and expertise. The data manager
coordinates and manages the collation and archiving of trusted data, to ensure current best
practice is followed and long term data availability. The data manager is also responsible
for maintaining an evergreen data management plan.
The asset owner defines what data, documentation and drawings (including as-builts) are
maintained, and for ensuring data availability and currency. Technical integrity assurance
should be based on a minimum set of defined drawings and documentation. The final
decision on documentation requirements is the responsibility of the eventual asset
manager. Storing this data shall conform to agreed asset specific data and document
management standards.
2.1.3 Data updates
Changes to information technology, applications and services should be managed
according to defined processes, to ensure information risks are assessed and appropriate
controls are implemented. Data should be built in a consistent manner, supporting
accurate interpretation and analysis which in turn promotes better data maintenance and
decision-making processes. Review and approval processes should control trusted master
data creating and labelling, such that the status of information is always clear.
2.1.4 Data integration
Data integration is required from several wide-ranging datasets including atmospheric,
water column, seabed, shallow subsurface/overburden, in-well, and reservoir sources.
The following data integration and management aspects should be considered during
the project planning and execution stages. Suitable specialist support should be engaged
where necessary (IT, data management, subsurface, geospatial/GIS, environmental,
geochemical, survey, metocean, etc.).
2.1.4.1 Data models
Relevant models should be utilized to support automation and standardization of data
storage, exchange, integration, and analysis. Examples include the SSDM (Seabed Survey
Data Model), PPDM (Professional Petroleum Data Management), WITSML (Wellsite
Information Transfer Markup Language), SEGY/SEGD (Society of Exploration Geophysicists
formats geophysical data – seismic and shallow geophysical) and P1, 2, 6 and 7-formats
(IOGP seismic and wellbore position data formats).
13
Seabed and overburden integrity monitoring for offshore CO2 storage
2.1.4.2 Live data streaming
This may be required, for example for seabed pressure monitoring, leak detection, subsea
CO2 detection etc. Delivery mechanism, storage medium, latency, bandwidth, redundancy,
and reliability should all be considered when designing the data transmission model, based
on the criticality, volume and update frequency of the data being streamed.
2.1.4.3 Spatial integrity of data
The majority, if not all datasets used or acquired have a spatial component (position).
For some datasets, positional accuracy may not be particularly important for integration
and analysis (e.g., low resolution regional data types). For many, however, positional
accuracy impacts appropriate integration with other datatypes (or time-series analysis)
and subsequent interpretation and business decision making processes. Thus, spatial
integrity management is important, from acquisition and processing, through data loading
and storage, to manipulation, visualization, and exchange/export. Appropriate Coordinate
Reference Systems (CRS) and coordinate operations should be fully defined and managed
for all aspects of the project.
2.1.4.4 Data visualization and interpretation/analytics applications
Several licensed applications may be required to integrate and visualize different
datatypes. Typically, software tools may comprise a combination of geophysical/geological
subsurface application/s, and an enterprise GIS (Geographic Information System). The
GIS component facilitates storage, integration, management, and visualization of several
atmospheric, water column, environmental, seabed and shallow geology components.
Appropriate management of the MMV enterprise GIS would typically be a core role for the
MMV specialist.
2.1.5 Building a GIS
Geographic Information System (GIS) software is a flexible and scalable geospatial
data integration, visualisation and analysis platform, employed across a broad range of
industries and businesses. IOGP members currently use GIS across the exploration and
production lifecycle to manage both surface and subsurface data. This existing industry GIS
experience, capability and structure is relatively easily transferable to offshore CO2 storage
developments. A shallow overburden MMV plan can be considered as another use case for
an organization’s enterprise GIS.
A key GIS strength is its ability to integrate a variety of data themes across an Area
of Containment (AoC), and Area of Influence (AoI). Highlighting spatial and temporal
relationships between infrastructure, interpreted geology, plume modelling, injection
profiles, monitored responses, and observable change features provides a powerful tool for
data driven decision making throughout the lifespan of an offshore CO2 storage project.
Due to the duration and complexity of an offshore CO2 storage project, a wide variety of data
are acquired, from initial baseline datasets to preventative and contingency monitoring
elements. This requires engagement of acquisition contractors to deliver various survey
scopes, including infield and downhole sensor deployment. Large data volumes and
diversity places significant focus on efficient and consistent data delivery and structure.
14
Seabed and overburden integrity monitoring for offshore CO2 storage
It is recommended that a multi-disciplinary team is established to steer development
of the GIS. It should establish organisational awareness of the system’s integration,
visualization, analytical and publishing role for current operational and containment status
at the user desktop, rather than as a specialist’s back-office tool. This establishes a key
complementary GIS role in visualizing the MMV plan.
The GIS will update as the offshore CO2 storage project progresses through the preinjection, injection, closure and post-closure phases, with the highest activity during the
pre-injection and injection phases. Ongoing data management support, however, will
continue through to post-closure, as highlighted in Figure 2.
Pre-Injection
Injection
Closure
Post-Closure
GIS development in support of the MMV Plan
3rd Party and
Baseline Data
Integration of Site Monitoring
Data
Compilation of existing
Company and 3rd Part data
representing the context of the
CCS Development, Including:
Integration of monitoring
datasets, demonstration of
seal integrity, CO2 Plume
extent and environmental
sampling that demonstrates
site injection Conformance
and minimal seisicity impacts.
Integration of monitoring
datasets acquired postinjection phase, to
demonstrate long term
containment of CO2 Plume,
and no adverse impact to
environment.
Ongoing integration of
datasets from (minor)
monitoring activity, to
demonstrate long term
containment of CO2 Plume,
and no adverse impacts to the
environment.
In case of Containment
breach, identified anomalies
subsurface and potentially
at seabed that demonstrate
location and magnitude
of emissions, impact to
environment and biosphere.
Prepare to Stakeholder
engagement for transfer of
liability.
GIS database used to evidence
agreed handover with
Government.
Administrative Boundaries,
Site Areas, Metocean
Currents, Seabed /
Environmental / Geochemistry
/ Subsurface Baseline, Well
Integrity, Fluid Migration
Pathways, Modelled Plume
Migration.
Preparing for
Site Closure
Site Handover
Reporting
Figure 2: Phase development and utilization of GIS for an offshore CO2 storage project
Two scenarios below illustrate how the GIS may be implemented, representing low and
high case system customisation and resourcing requirements:
Cartographic reference: in a relatively simpler application, the GIS visualization may provide
a static cartographic reference across the AoC/AoI, utilizing, as a minimum, the GIS data
layering capability to develop various themed map products for reporting. With appropriate
version control, this GIS implementation style still enables access to historical reference
data, as new data is incorporated into the active dataset.
Spatial/temporal dashboard: a more complex solution has a stronger focus on
digitalization, via a dynamic visual dashboard of spatial features and temporal monitoring
data, representing injection sequence history and response. As an production/injection data
can be displayed alongside available pressure response data, co-located with near-surface
observations and evaluated against available plume migration models.
Project teams may focus on a cartographic reference solution initially, but as the project
matures into injection, a spatial temporal dashboard solution is likely to develop, to
support MMV plan accessibility across multiple disciplines, and to support better-informed
business decisions.
15
Seabed and overburden integrity monitoring for offshore CO2 storage
The associated GIS development plan and resourcing requirements should be clearly
represented in the project’s data management plan.
2.1.6 Seabed and shallow overburden data management
For seabed and shallow subsurface/overburden data management, implementation of the
IOGP Seabed Survey Data Model (SSDM) is recommended. Originally developed as an oil
and gas industry standard for storing, managing, visualizing, and analyzing seabed, shallow
sub-surface, and environmental sampling survey data, this fully scalable and extensible
model is equally applicable to the management of seabed and shallow-subsurface surveys
for offshore CO2 storage projects.
This model is described in the following documents:
• IOGP Report 462-1 - Guidelines for the use of the Seabed Survey Data Model: this
Report provides the SSDM specification for oil and gas exploration and production,
handling collection of various seabed and shallow-subsurface survey data in
GIS format.
• IOGP Report 462-02 - Guideline for the delivery of the Seabed Survey Data Model: this
Report provides SSDM guidance to contractors, covering structure and deliverable
requirements for GIS data provided to oil and gas operators. Geographic data
modelling terminology is used to describe data structure, attribution, cartographic
representation, and delivery.
The SSDM provides an industry-recognized data model, and a starting point for scaling and
extension as required to support management of any additional CCS MMV datatypes not
already directly covered by the model, as well as the management of similar data themes at
a deeper geological setting within the containment complex.
Topics currently not covered in the SSDM include management of various seabed and
downhole (continuous) sensor data, plume modelling data, and other types of contextual
GIS data. There is some allowance for water column data within SSDM’s environmental
sampling objects. While SSDM v2 was designed primarily for static geophysical seabed
site surveys, and thus continuous measurement data is not directly catered for, SSDM
is extensible, so other use cases, including offshore CO2 storage monitoring, can be
incorporated into the model, as part of an enterprise GIS solution.
For pipeline data models generally, and the management of seabed data acquired via
pipeline inspections, including interfacing with SSDM, see IOGP Report 462-3 - Interfaces
between pipeline data models and the OGP Seabed Survey Data Model.
2.1.7 Managing geodetic integrity
In support of broader development of the Enterprise GIS database for an offshore CO2
storage project, because ‘location’ is the key integration attribute, data from seismic
interpretation and well data management systems often requires the verification of legacy
coordinate reference systems and other positioning elements (along with previously
acquired shallow geophysical, oceanographic, environmental data etc.). Table 1 outlines
some key references for spatial integrity management of various legacy and newly
acquired datatypes.
16
Seabed and overburden integrity monitoring for offshore CO2 storage
Table 1: Key references for spatial integrity management of various legacy and newly
acquired datatypes
Theme
Purpose
Key Reference
Geodetic integrity
A GIS environment integrates a
range of legacy and new data.
Ensuring that an appropriate
contemporary Coordinate
Reference System (CRS) for
the location of interest, along
with associated transformation
parameters for legacy CRSs is key
to accurate mapping/visualization,
analysis of spatial relationships,
and the integrity of reported
coordinates, both horizontal and
vertical.
• IOGP Report 373-01 - Geodetic
awareness guidance note
Offshore CO2 storage projects
require specific awareness of
relevant legacy wells and detailed
planning of both water producing
and CO2 injection wells. Spatial
verification of legacy and planned
wellbores is a key component of
operating performance and risk
management. The combination
of well and seismic data required
particular care with respect
potential uncertainty in reported
coordinates or location-based
references one, other, or
both datatypes.
• IOGP Report 373-16 - Guidelines
for the quality control of
proposed well coordinates
Wells
17
• IOGP EPSG Geodetic Parameter
Dataset
• IOGP Report 373-21 -Grid
Convergence – Geomatics
guidance note 21
• IOGP Report 373-24 -Geomatics
Guidance Note 24 – Vertical data
in oil and gas applications
• Geospatial Integrity of
Geoscience Software (GIGS)
• IOGP Report 483-7 - P7/17
Wellbore Positioning Data
Exchange Format (and User
Guide)
Seabed and overburden integrity monitoring for offshore CO2 storage
Theme
Purpose
Key Reference
Seismic
A key workflow is end-to-end
management of seismic data
within trace interpretation systems,
and interpreted horizon and fault
export into the GIS environment.
Referenced guidelines cover
2D, 3D and time lapse seismic
and the 3D seismic bin grid data
model.
• IOGP Report 483-1u - OGP
P1/11 Geophysical position data
exchange format – User Guide
• IOGP Report 483-6u - IOGP
P6/11 Seismic Bin Grid Data
Exchange Format - User Guide
• IOGP Report 483-6g -Guidelines
for the use of the P6 Bin Grid
Data Model
Shallow subsurface and seabed
geophysical data
Shallow seismic datasets (high
• IOGP Report 373-18-1 resolution and ultra-high resolution
Guidelines for the conduct of
seismic, and sub-bottom profiler)
offshore drilling hazard site
broadly may be treated the same
surveys
as reservoir seismic from a spatial
• IOGP 373-18-2 - Offshore
integrity perspective. Other key
Drilling Hazard Site Surveys –
CO2 storage monitoring datasets
Technical Notes
(e.g., multi-beam echosounder
(MBES), and side-scan sonar
(SSS) imagery), along with other
datasets such as seabed pressure
sensors (depth), inclination and
acoustic/laser leak detection
imagery also require careful spatial
management and integration,
whether point data or imagery, or
interpreted results.
Environmental, oceanographic
data satellite/ aerial imagery
The spatial elements of such
• IOGP Report 629 - Application of
datasets typically is of lower
Remote Sensing Technologies
importance, due to their often
for Environmental Monitoring
more regional scale. However,
environmental and oceanographic
data is often point sampled’ and
CRS and positioning integrity is
required to ensure accurate spatial
integration with other datatypes,
allowing appropriate conclusions to
be drawn from the attributes.
Likewise, appropriate georeferencing is required for satellite
and aerial imagery.
2.1.8 Gathering baseline datasets
The near-surface site characterization of the CO2 storage site should be well understood
to determine what monitoring readings constitute anomalous and then to determine
their source. Section 2.2.2 details the typical datasets that would be used in monitoring.
When considering shallow monitoring, the focus is on the determination of containment
breaches, rather than conformity or confidence.
18
Seabed and overburden integrity monitoring for offshore CO2 storage
At the highest level, these fall into the two categories of being geological characteristics
and oceanographic ones. The specifics of these will be examined throughout the guidance
sections of this document. To highlight the importance of a robust dataset it is best to
introduce the concepts of how a leak will impact these categories.
Geological symptoms will be the presence of features of fluid flux disturbance on the
sediment, chimney structures and pockmarks visible through geophysical examination
while the sediment chemistry can give indications of contamination. Oceanographic
measurements take place in the water column where a gaseous phase leak will provide a
bubble stream while CO2 concentration will be elevated causing a reaction in the
carbonate system.
The benthic region is highly dynamic with the movement of water, daily and seasonal
factors forcing variability in many of the parameters we are looking to give us an indication
of a leak. These are examined in more detail in Section 2.1.4. At this stage it is sufficient to
simply identify that a baseline is required to identify anomalous events against, and that the
baseline itself has a natural variability. The longer a baseline monitoring campaign is, the
more valuable it will be to capture this variability.
2.1.9 Use of existing datasets
Most injection sites will have pre-existing datasets from their use as production sites,
exploration, or research. Model data may also prove useful, especially in exploring the
exposure to and result of risk events. Work from adjacent industries, for example offshore
wind site surveys, could also prove valuable.
All legacy data will have to be verified to determine:
• Its relevance to CCUS applications, as the data was unlikely to have been collected for
this purpose
• The current validity of the data, given the dynamic nature of the water column and
shallow seabed
• The repeatability of the data: was the original collection methodology sufficiently
temporally and spatially accurate
Given the high level of assurance needed to prove the baseline state of the storage area,
it is unlikely that existing data will prove sufficient on its own. The use of existing datasets
would prove valuable in demonstrating changes prior to a fresh baseline, to establish
natural variation.
2.1.9.1 Shallow geology and seafloor morphology
Shallow geology and near-surface geophysical/hydroacoustic datasets (using a SubBottom Profiler (SBP), Multi-Beam Echo Sounder (MBES), and/or Side Scan Sonar (SSS))
could be expensive to acquire, in particular over wide areas. Using legacy datasets, when
available, could be attractive at a preliminary stage, and would typically be used to identify
active natural leak characteristics such as pathways through the sediment and pockmarks.
Identifying the natural range of pockmark sizes and locations would prove very valuable
in change monitoring during injection operations. Datasets would need to have sufficient
resolution to capture these leak features. For shallow geology monitoring, time-lapse
19
Seabed and overburden integrity monitoring for offshore CO2 storage
approaches using any technology (HR seismic, MBES, SBP), it is important to consider and
be consistent between survey tool parameters such as pulse file used (pulse length, power,
frequency range) and acquisition parameters (direction of survey, altitude, and position).
Leakage pathways and seabed surface expressions will be dependent on leak rates and
shallow overburden composition, it is therefore difficult to define absolute resolutions
required and baseline conditions will be limited by the technology available.
The credibility of legacy data will also need to be carefully assessed concerning its age and
change forcing factors. In areas with high sediment mobility driven by seabed composition
and tidal and current forcing, features can change rapidly. In such a case, historic data
would be extremely useful with new data to assess natural change. Seabed displacement
may also be measured though bathymetric data. Any induced seabed deformation through
injection operations is likely to be in the centimetric range at most and differences caused
by measurement techniques should be carefully considered.
Marine environment and hydrodynamics
The marine environment covers both the biology of the storage site and chemistry of the
water column and shallow subsurface. It is highly likely that an environmental impact
assessment, as defined by the regulator, will have taken place, which will provide a
statutory biological baseline even in the presence of large amounts of historical data. In
release experimentation the chemical parameters of pH, dissolved CO2, nutrients, nitrate,
phosphate and O2, were identified as leakage indicators for CO2 and markers to attribute
the source of any changes to biogenic or injection activity.4 These chemical parameters are
subject to large diurnal and seasonal variability. In these circumstances, as broad a dataset
as possible is desirable so as to fully understand the natural range. A historical record of
these parameters would be extremely useful but given the very specific circumstances
for their collection it is unlikely that they would exist. The paucity of this data may drive a
monitoring strategy based on relative changes observed rather than thresholds
being exceeded.
For a site with existing infrastructure, there are likely to be suitable hydrographic datasets
from preconstruction, and construction measurement campaigns, and potentially also
ongoing integrity management campaigns. These will give local forcing mechanisms
for dispersion of leaks at higher risk points of interest, such as the injection site.
Dispersion via a leakage pathway somewhere in the whole complex site unidentified in site
characterization will be on a scale impractical for a comprehensive monitoring campaign.
In this case, adjacent legacy datasets may be used in conjunction with tide and current
modelling to understand leak dispersion.
Biological receptors
From the release experiments conducted with close observation of marine wildlife in
the UK, no impact was observed in bivalve organisms and megafauna but impacts were
observed on microbial and microbenthic community structure. Nevertheless, overall use of
responses in biological receptors as an indication of leaks, and by extension their individual
or population reactions to leaks, is considered unreliable.
4
Dean M et al, 2020
20
Seabed and overburden integrity monitoring for offshore CO2 storage
2.1.10 Capturing temporal variations
Figure 3 shows the variation and range of pH modelled for two potential storage sites in
the UK North Sea. The significant range experienced at all stages of the year indicate the
complexity of chemical detection in the context of natural variability. These ranges are
typical of shelf seas that overlay storage complexes, with an annual variation of 0.2-0.4 pH
Marine deployable sensors can reliably detect pH with a resolution of 0.01pH and so this is
determined to be the threshold for detectability.5
Figure 3: Climatology of modelled pH ranges in the North Sea (a) northern region which seasonally
stratifies, (b) southern region which remains mixed throughout the year
2.1.11 Identification of missing data or survey gaps
Section 3 (Technical Notes) of this document provides a detailed list of the data and surveys
required for an MMV plan for the relevant regulatory area. An overview of likely datasets is
provided in Section 2.2.2. As discussed in Section 2.1.3, legacy data may be used so long as
it passes criteria on relevance, currency, and repeatability and completeness of metadata. If
the data fails to meet these criteria, then a new measurement campaign should
be undertaken.
5
Blackford J et al, 2014
21
Seabed and overburden integrity monitoring for offshore CO2 storage
There may be synergies with other developments in the area over the use of data or
leveraging assets in the area. That is to say, if a vessel is already in the area conducting
preconstruction surveying for windfarms, it would save costs to identify these opportunities
early and combine missions. In limited cases, it may be possible to fill measured data gaps
with model data where there are enough measured data points to calibrate a model or
otherwise demonstrate high credibility. Caution should be applied to this methodology, as it
will create an artificial baseline which anomalies would be measured against.
2.2
Developing the near-surface MMV plan
2.2.1 The near-surface MMV - a key element of the overall MMV programme
The near-surface MMV (shallow monitoring) is an intrinsic element of the overall MMV plan
which is comprehensive in space and has distinct phases of operation. The interconnection
between the near-surface MMV and the overall risk-based MMV programme is described
below in terms of the CO2 storage operation phases.
2.2.1.1 Pre-injection phase
The containment subsurface characterization of a geologic storage site is performed to
identify potential leakage risks (wells, faults). Leakage scenario studies are key in this
phase and a storage site may disqualify if deeper and shallower risk features have the
potential to connect. As part of this phase, baseline data should also be collected to identify
near-surface risk areas (active seepages, protected species) and to enable comparison of
data (to establish conformance and verify containment) with later phases in the project.
Some projects may reuse existing near-surface data from hydrocarbon phases of a
depleted reservoir. Synergies should be identified with other environmental
permitting efforts.
2.2.1.2 Injection phase
The expectation is that subsurface and borehole monitoring data (deep-focused) will
provide early warning should loss of containment be expected. Should such alerts occur,
a review of the containment risk-assessment (using the bowtie for example) would be
initiated which in turn could trigger contingency monitoring including near-surface
monitoring over the area of interest. In the unlikely case of emission to the marine
environment, quantification of the emitted volume is required, and corrective measures will
have to be implemented. Close and transparent collaboration with the regulator will
be expected.
If no loss of containment is suspected, time-lapse near-surface monitoring focusing on
high-risk areas (wells, natural seeps, pockmarks) to verify site performance may still be
required by the regulator and other stakeholders.
22
Seabed and overburden integrity monitoring for offshore CO2 storage
2.2.1.3 Closure phase
After injection ends, containment will have been verified and conformance established, i.e.,
subsurface models have been calibrated with MMV data and the long-term behaviour of the
CO2 plume, including potential further migration, is understood. Post closure near-surface
monitoring data will be collected to demonstrate the absence of undesired impacts to the
marine environment. Collectively, the MMV data covering all phases and areas of a CO2
storage project will enable transfer of long-term responsibility to the competent authority.
2.2.2 Summary of typical datasets required
The near-surface site characterization of a CO2 storage complex may need datasets
collected for geophysical, shallow geotechnical sampling, environmental and hydrodynamic
parameters, to enable near-surface MMV plan definition. The collection methodology for
the monitoring measurement campaign typically should be the same, or at least similar to
the baseline campaign.
Geophysical datasets are examined in detail at Section 3.1.2. These are shallow subsurface
geophysics for the identification of various near surface and surface particular features
related to fluid flow to be considered as shallow hazards, such as shallow gas, chimneys,
fractures, and faults that may act as seal bypass providing fluid flow pathways to shallower
depth and pockmarks that are the seabed expression of focused fluid seepages at seabed.
Bathymetry will also provide an indication of breaches of containment or conformity as
seabed deformation will provide an expression of CO2 storage behaviour.
Near-surface datasets are examined in detail in Section 3.1.3. These datasets fall into the
categories of chemical and biological indicators of:
• Biological activity which may influence leak indicators
• Carbonate chemistry
Ecosystem data
Hydrodynamic datasets are examined in detail at Section 3.1.4. These are principally for
the identification of the current conditions so that the water movement can be accurately
modelled, and the chemical dispersion of a leak understood.
2.2.3 Ways of handling long-term variability/continuity (drifting baseline)
Natural variability presents a challenging aspect to the shallow monitoring of the storage
complex, shifting the baseline by which anomalies can be detected. In geophysical
measurements there will be an evolving state of the seabed, such as sand bar migration,
erosion. Although this is a complexity, it is unlikely to mask leakage events, a difficulty
chemical monitoring of the water column is highly exposed to. The carbonate system of the
water column can be measured by factors of dissolved inorganic carbon (DIC), dissolved
CO2 (ρCO2), total alkalinity (TA), and pH; all of which are subject to natural change driven
by processes such as respiration, photosynthesis, formation, and breakdown of shell
structures and CO2 exchange with the atmosphere. Increased CO2 causes acidification in
seawater through the formation of carbonic acid and release of hydrogen ions.
23
Seabed and overburden integrity monitoring for offshore CO2 storage
Increased atmospheric CO2 has already resulted in a mean sea surface pH reduction from
8.2 to 8.1.6 Under the median IPCC scenario of atmospheric carbon increasing to 500ppm
by 2050, a decrease of pH of approximately 0.1 is forecast in the UK North Sea. Evidence
from observations shows that the UK is consistent with global trends.7 The trend for pH
being -0.0036±0.00034 pH units per year for the North Sea.
While this variation and trend is notable, the effect of it will be dwarfed by the diurnal
and seasonal variability discussed in Section 2.1.4, and management techniques will be
contained within these shorter-term fluctuations.
2.2.4 Identification and definition of anomalous events
Any measurement in the shallow overburden and at seabed of particular proxies that
indicates an unexpected behaviour of the stored CO2 is an anomalous event. This is reliant
on a thorough monitoring campaign to establish the baseline conditions and reliable
modelling of expected changes during injection to determine what is truly an anomalous
event. An anomaly response plan, with escalation measures is discussed at Section 2.2.8.
It should be noted that all the anomalous features listed below can either occur naturally,
already be present, or be due to events unrelated to CO2 injection. This further emphasizes
the need for robust baselining to ensure that existing or naturally explainable features are
not attributed to injection activities.
2.2.4.1 Geophysical anomalies
Geophysical anomalies will be taken from the baseline conditions discussed in Section
6.1.1. Features detected that would be an indication of loss of containment would be
accumulation of gas in shallow sediment, chimney, and fracture structures that act as
conduits of fluid flow and pockmarks as the result of fluid flux at the sediment surface.
Bathymetry data indicating seabed deformation can also give indications of deep or shallow
changes that would indicate expected performance against conformance or breaches
in containment.
While more closely linked to the near-surface methodologies, changes in the sediment
chemistry can also provide leak indications. This may prove more stable than water column
measurements as it will be less exposed to hydrodynamic forcing and biological effects.
2.2.4.2 Environmental/chemical anomalies
Environmental and chemical anomalies will be measured against the baseline conditions
discussed at Sections 3.1.3 and 3.1.4. Chemical detections will indicate the loss of
containment through the presence of tracer elements, precursor materials (brine) or
changes in the carbonate system. Changes in the chemical composition may be caused by
displaced materials, typically formation brine, which may or may not be anomalous.
6
7
Birchenough S, Williamson P, and Turley C, 2017
pH and ocean acidification, UKAMMS, https://moat.cefas.co.uk/ocean-processes-and-climate/ocean-acidification/
24
Seabed and overburden integrity monitoring for offshore CO2 storage
The most practical parameter to measure to detect the presence of CO2 is pH (see Section
3.2.2.1). A natural range of 0.2-0.4 pH can be expected at continental shelf storage sites,
which will mask a leak to sensors with a practical detection resolution of 0.01pH. This
drives a methodology of identifying outlying data points rather than absolute thresholds.
Gaseous phase leaks will produce a bubble plume in the water column even if leaked CO2
will likely be rapidly dissolved into water. Acoustic surveys are most likely going to detect
emissions although chemical sensors would be relevant to attribute and quantify when a
leak has been detected.
2.2.5 Requirements for verification and attribution
With leak features being both naturally occurring and subject to natural variability,
verification of anomalies as true provides a challenging task. The anomaly response plan
(Section 2.2.7) suggests a methodology for this.
There is a high probability of false positive anomaly detections against individual
parameters. For a confident detection, verification will require multiple detections of a
single parameter and/or corroboration against other parameters (co-variance).
Attribution is the requirement to identify the cause of any anomaly as linked to injection
activities and in multiple user areas, the operator responsible for an anomaly. There
is a strong coupling between verification and attribution requirements. Both require
natural causes to be discounted. This starts with assessing the baseline data from store
characterization and understanding the information from the deep-focused monitoring
situation. Leakage mechanisms in storage units seals and overburdens need to be well
understood. A shallow monitoring ‘detection event’ without correlation with a deeper
feature is extremely unlikely. If correlation is established this would then also provide
evidence for attribution for the origin of the leak as being from the storage complex
(and the responsible operator). Shallow monitoring chemical sensor requirements for
verification and attribution are examined at section 3.2.2.1. Phosphate and nitrate sensors
are used to determine whether changes in pH or ρCO2 are due to biological activity.
The need for temporal and spatial context of information drives requirements in data
handing and display. This is discussed in Section 3.1.1.
The use of tracer elements assigned to operators to aid attribution has been suggested.
However, the inclusion of tracer elements into the sequestered CO2 is not yet confirmed as
standard practice and may not be practicable.
25
Seabed and overburden integrity monitoring for offshore CO2 storage
2.2.6 Routine surveys versus targeted surveys
The survey strategy will be a key part of forming the overall monitoring plan. Reviewing
the regulations for monitoring across the UK8, EU9, Australia10 and Japan11, there is
broad recognition that monitoring periodicity is driven by specific store characteristics to
determine conformity and containment and is not explicitly defined. It should be noted that
the US has the additional complexities of conforming to state and federal laws.
While a periodicity is not stated by any of these jurisdictions, there are several parameters
that are, by their nature, continuously monitored such as volumetric flow, temperatures,
and pressures at the injection head. The wide area monitoring plan for the rest of the
storage site is then to be submitted by the operator, demonstrating sufficient reasoning for
their frequency of surveying. This section will examine the factors to be considered when
determining this frequency.
Routine surveys will be at programmed intervals to cover set areas. Seismic imaging12 will
need to be at a frequency to determine containment and conformity to modelled plume
migration. Conformity will demonstrate the plume is behaving as expected and avoiding
high risk areas, such as outcropping and old infrastructure. If high levels of confidence
can be established on the containment from deep monitoring, then shallow wide area
monitoring may not be required. If it is determined that wide area shallow monitoring is
required, there are several concepts of operation that have emerged for monitoring of the
seabed and water column over the storage complex. These are examined in section 3.2.
This has largely focussed on the use of uncrewed surface and subsurface platforms for
chemical and hydroacoustic suits. Mobile chemical sensors will be extremely sensitive to
high spatial and temporal fluctuations in the baseline conditions of the carbonate system.
As such periodicity will not form a major consideration in mobile chemical sensors as the
they will look to detect outlying measurements (jumps or step changes) within their
own dataset.
Targeted surveys will either be as a response to concerns driven by known high risk
factors or as part of anomaly response, the latter of which is discussed in Section 2.2.8.
Where there is a high-risk factor, such as the CO2 plume encountering abandoned
infrastructure or influencing flux of a saline aquafer outcrop, a targeted near-surface
survey may be conducted at this point. Careful consideration should be applied to whether
this can be adequately captured by a single survey, or whether continuous monitoring
needs to be established via a seabed lander.
8
9
10
11
12
The Storage of Carbon Dioxide (Licensing etc.) Regulations 2010, itself referencing the EU regs below
DIRECTIVE 2009/31/EC, Annex II
Environmental Guidelines for Carbon Dioxide Capture and Geological Storage - 2009
Act on the Prevention of Marine Pollution and Maritime Disaster
These will have to be applied for under The Offshore Petroleum Activities (Conservation of Habitats) Regulations, 2001
26
Seabed and overburden integrity monitoring for offshore CO2 storage
2.2.7 Anomaly response plans
A formal anomaly response or corrective measures plan should be written by a responsible
operator and customized to the particular storage formation. Actions on breaches of
containment are outside the scope of this document, but will be dealt with in accordance
with the requirements of the licensing authority, acting in accordance with the operator’s
internal emergency response plan as part of the wider report on major hazards (OGC/IOGP/
IPIECA Recommended Practice for a Common Operating Picture for Oil Spill Response
is a good example on emergency response). Reporting will be in accordance with the
requirements of the licensing authority. In the absence of specific CCS regulations covering
leakage response, best practice should be taken from the oil and gas and MARPOL
regulations of the jurisdiction.
The severity of the anomaly detected will drive the urgency of the response plan. At
the lowest end, it may simply be an anomaly that differs from modelled conformity
with no evidence of compromised containment, in which case the understanding of the
performance of the store can be updated.
For anomaly detection that indicate the breach of primary containment, which is most
likely as part of deep monitoring, efforts should be made to confirm other containment
mechanisms. This may include further analysis or recollection of the data to establish the
integrity of secondary or higher-level containment mechanisms.
Anomalies in shallow monitoring present more difficulties as they indicate a complete
failure of containment mechanisms and are subject to a far more dynamic marine
environment. Such environment is much more likely to present false positives, especially
when analysing chemical data against thresholds that may indicate a leak but could be due
to biogenic or other factors. Actions taken here are to report the incident as required by the
licensing authority and internal safety processes. Efforts should then be taken to establish
the veracity of the anomaly, this may be by repeat surveying, analysis of the data and/
or establishing permanent monitoring at a position of interest. While detection systems
are commonly referred to as Measuring, Monitoring and Verification, many have an initial
functionality of detection without measurement. If quantification of a leak is required, then
care should be taken to deploy the correct system and methodology to achieve this. An
example of verification and escalation methodology is presented in Figure 4.
27
Seabed and overburden integrity monitoring for offshore CO2 storage
DETECTION
Survey-based
Bubble detection with ship
or AUV
CO2(g,d) detectable?
NO
Fixed Installations
with chemical or acoustic
sensors CO2 (g,d) detectable?
Chemical sensors on AUV
or CTD
CO2(g,d) detectable?
YES
Y
Detection of leakage of CO2
likely high leakage rate
(g,d)
N
N
No leakage
detectable
N
Presence of CO2 (g,d) and a
plume height approx. >2m
Benthic chambers, pH eddy
coveriance, Lab on Chip
gradient
CO2(g,d) detectable close to
sediment?
Y
pH optodes, microprofiler,
sediment geochem
CO2 (g,d) detectable in
sediment?
Y N
Y
Low or high leakage rate
of CO2 (g,d) close to the
sediment
Higher leakage rate with
plume height ca.>1m
No leakage
detectable
CO2(g,d) detected in sediment
LEAKAGE DETECTED
VERIFICATION & ATTRIBUTION
Process-based
Stoichiometry / Simulation
based on sensor data
CO2(g,d) anomaly detectable?
Y
N
Tracer-based
Natural or inherent tracers
Tracers detectable?
CO2 attribution to
reservoir not possible
N
Y
CO2 attribution to
reservoir not possible
CO2 from specific
reservoir
CO2(g,d) anomaly
LEAKAGE VERIFIED AND ATTRIBUTED
QUANTIFICATION
Bubble quantification from ship
or AUV, passive acoustics
CO2(g,d) quantification possible?
N
Y
Quantification of CO2(g)
leakage, likely high leakage flux
Lab on chip gradient, benthic
chamber
CO2(g,d) quantification possible?
Y
N
Computed approach based on DIC/
pH and currents
Quantification of CO2(d) leakage
Calculations of CO2(d) flux
LEAKAGE QUANTIFIED
Figure 4: Flow chart showing a potential monitoring strategy for offshore CO2 storage complexes
based on the experience acquired during the STEMM-CCS release experiment (Lichtschlag et al.
2021)
28
Seabed and overburden integrity monitoring for offshore CO2 storage
3
Technical notes
3.1
Baseline methods
3.1.1 Geophysics
As for the conduct of CO2 subsurface storage site qualification and baseline, it is required
to assess the near-surface geological context to identify any processes witnessing natural
fluid migration pathway. Existing migration pathway in the shallow overburden may be
indeed preferentially re-used by CO2 in the case of CO2 migration outside the
storage complex.
Oil and gas exploration and production projects have shown the existence of various
near surface and surface particular features related to fluid flow. These features are
shallow gas, chimneys, fractures, and faults that may act as seal bypass providing fluid
flow pathways to shallower depth. Pockmarks are the result of focused fluid seepages
at seabed. They may be related to shallow dewatering processes due to consolidation of
shallow sediments but may also be the seabed expression of fluid flow having a deeper
origin. Pockmarks occur in both random (isolated) and non-random distributions; the
latter, known as pockmark clusters, are generally associated with shallow overburden
structures as chimneys or faults.
Near-surface natural fluid flow features may have implication for migration of CO2 in the
shallow overburden and to the near surface as they may act as fluid pathways. Hence, it
is necessary to understand the baseline status of these natural near-surface fluid flow
features to identify any preferential CO2 migration pathway in case of CO2 migration from
the storage complex. Differing rates of flux from these natural fluid flows may also be early
indications of deeper changes. A good understanding of these fluxes is also required to
prevent their attribution to offshore CO2 storage activities, when they may be
perfectly natural.
Evidence of the processes of migration and rates of fluid flow through the shallow
overburden and detection of these seabed features rely on high resolution geophysical
methods and equipment that are described in the following guidelines and standards:
• IOGP Report 373-18-1 - Guidelines for the conduct of offshore drilling hazard site surveys
describes good practices for conducting geophysical and hydrographic site surveys of
proposed offshore drilling locations.
• IOGP Report 373-18-2 - Conduct of offshore drilling hazard Site Surveys – Technical
Notes provides supporting technical information for the guidance in IOGP
Report 373-18-2.
• ISO 19901-8:2014, Petroleum and natural gas industries – Specific requirements for
offshore structures – Part 8: Marine soil investigations
Even if these guidelines and standards have been developed for oil and gas industry use,
their content is fully applicable for near surface geological assessment dedicated to
CO2 storage.
29
Seabed and overburden integrity monitoring for offshore CO2 storage
3.1.2 Environment
Providing an absolute environmental/ecological baseline of the water column over a store
is an extremely difficult task given the high levels of variability observed. This variability is
discussed in Sections 2.1.4 and 2.2.4. If historical data is available, then it can be used to
mitigate the difficulties caused by this variability. The use of this legacy data is covered in
section 2.1.3. Table 3 covers the typical parameters that would be covered to chemically
and biologically characterize the environment. This largely focuses on establishing the
carbonate system of the monitored area, with sensors to determine whether anomalies
may be due to leaks or biological activity. These parameters are discussed with the
hydrography at Section 3.1.4.
These chemical parameters have an annual wave form of variation, with smaller diurnal
sub-signals. As such to characterise the system correctly the minimum data collection
period would be 1 year. Additional data beyond this would prove extremely valuable in
determining the natural range outside of the core signal. Chemical variation is not only
temporal but could also be extremely localized constrained by the hydrodynamic conditions.
As such special points of interest, such as the injection point, outcropping and the like
should be individually baselined, as well as suitable control points in the vicinity of the
store. This is most effectively achieved by deploying a lander at the site with a chemical
detection suite.
The requirement for the monitoring campaign may be so challenging, that novel
approaches need to be considered. This may include the use of modelled data and
monitoring methodologies reliant on rates of change in parameters rather than detection
against trigger thresholds.
3.1.3 Metocean and geochemical data requirements
It may be necessary to establish a baseline of metocean and geochemical data and should
be based on different sets of information:
• an understanding of the natural environment, the so-called baseline, which includes
physical oceanographic parameters (currents, sea temperature, salinity), and
geochemical parameters (DIC, pH, nutrient concentrations, total alkalinity, etc..) that
provide insight into the dynamics, evolution, and interactions of CO2 (both gas and
dissolved phase),
• the resulting carbonate chemistry and potentially co-variables such that CO2 leakage
can be reliably detected, located, and quantified,
• an understanding of the biological communities, their sensitivities, dynamics and
social or economic importance such that any impacts may be assessed.
Figure 5 shows the actions required during each phase of a typical offshore CO2 storage
project and the corresponding deliverables. Which deliverables are required, and with what
level of detail, depends on the availably of existing data, the size of the project, and the risks
of any CO2 leakage. More details on each deliverable will be given below.
30
Seabed and overburden integrity monitoring for offshore CO2 storage
ASSESS
A. Desk study of the
relevant metocean
and geochemical
datato determine
baseline
SELECT
DEFINE
EXECUTE
OPERATE
B. Identify existing data
and collect new water
samples to determine
concentration of water
property and geo
chemical parameters
C. Current profile
measurement
campaign
D. Apply a highresolution
regional current
(hydrodynamic) model
E. CO2 dispersion model
F. Perform model test
runs and sensitivity
studies of the model
G. Maintain and run
combined model
during accidental
release of CO2
H. Carry out impact
assessment of
CO2 leak on water
properties and
biological communities
I. Conduct monitoring
CO2 in the enviroment
and maintain
equipment
Figure 5: Main actions during phases of offshore CO2 storage and the corresponding deliverables
3.1.3.1 Determine the baseline (desk study)
The physical parameters that drive the distribution of CO2, as well as geochemical
parameters, which improve reliability of CO2 detection and characterization, should be
considered. Table 2 gives an example of what parameters can be considered as part of a
baseline study. This could be observational data and model data, depending on what
is available.
31
Seabed and overburden integrity monitoring for offshore CO2 storage
Table 2: Content of a typical baseline study
Obtain profiles of:
Carbonate chemistry – analysis
Ecosystem data
• Temperature (C)
• Total alkalinity vs salinity
• Salinity (ppt)
• DIC versus potential
temperature
• Calcium carbonate (CaCO3)
reliant organisms
• Oxygen (µmol/l)
• Nitrate (µM)
• Phosphate (µM)
• NDIC versus NPO4
• NDIC versus NNO3
• Benthic fauna (corals,
crustaceans, etc..)
• Multi-cellular organisms and
fish
• Sediment-dwelling and benthic
organisms
• Silicate (µM)
• Total Alkalinity (µmol/kg)
• Bacteria, nanobenthos and
meiobenthos
• DIC (µmol/kg)
• pH
Cross sections (depth x distance):
Leak detection indicators:
Time series (multiple seasons):
• Potential temperature
• pCO2:O2 ratio (per season)
• Current speed and direction
• Temperature
• Sea temperature
• Salinity
• Salinity
• pH
• pCO2
Depending on the location of the offshore CO2 storage project, some data may already be
available in the public domain. There are numerous data sources that can be consulted:
• British Oceanographic data centre, https://www.bodc.ac.uk/
• The surface ocean CO2 atlas, https://www.socat.info/
• Active Archive centre for Biochemical Dynamics, https://daac.ornl.gov/about/
• Pangaea, https://pangaea.de/
• European Marine Observation and data network (EMODNET)
https://emodnet.ec.europa.eu/en
• International Council for the Exploration of the Sea (ICES)
https://www.ices.dk/Pages/default.aspx
3.1.3.2 Data collection: water property and geochemical parameters
Additional data have to be collected when the desk study (deliverable A and B of Figure
4) does not result in sufficient data to determine a proper baseline, which reflects all site
specific and seasonal characteristics. Costs of the data collection are largely driven by
the cost of a vessel’s to service the measurement equipment. As the data needs to cover
seasonal changes, multiple surveys during a year are required. Second, as concentrations
of most geochemical parameters typically show a noticeable gradient in the water column,
multiple samples per location are required. There are two types of sampling methods:
• Discrete sampling of the water column (traditional CTD/rosette, glider)
• Automated measurements of near sea-floor hydrochemistry and carbonate chemistry
32
Seabed and overburden integrity monitoring for offshore CO2 storage
parameters with sensors deployed onto ROV or landers or fit for purpose AUV
3.1.3.3 Current profile measurement campaign
The need for any current profile data is largely controlled by the quality of the existing
measured full water column current profile data (e.g., via ADCP) and model data. Different
from wind, waves, and basic water property data (temperature and salinity), which
are often very well known, currents can be very complex and show a lot of spatial and
temporal variability, which makes modelling them very challenging. In some areas, such
as large parts of the North Sea, the level of knowledge on current profiles (both models
and observational data) may be sufficient and no further data collection is needed. In
many other areas, we need to collect these data. To capture the seasonal variability, it is
recommended to collect at least one full year of data. Cost and schedule efficiencies can
be achieved when the campaign to collect current data includes water properties data
collection (deliverable C of Figure 5).
3.1.3.4 Apply a high-resolution regional hydrodynamic model
Currents can be driven by tides, atmospheric forcing (wind), density gradient, riverine
outflows, seabed/shoreline configuration and bathymetry and impacted by the Coriolis
effects. In shallow water areas (water depth less than 20-25 m), currents can often be
described by a certain near-constant profile shape (for tides or for winds) and a 2D model
may be sufficient. However, in most cases, a 3D approach with a vertical layered grid is
required to be able to model the main processes. For instance, the central North Sea is
highly stratified during the summer and well mixed during the winter period, which has
a major impact on the currents and vertical profiles of temperature and salinity. Only a
3D model can resolve this. A horizontal resolution of 5-10 km is typical for most current
models. However, depending on the location, a finer horizontal resolution (1-3 km and even
higher) may be required, particularly in areas with significant horizontal density gradients
induced by, for example, an outflow of fresh water and topography changes. Increased
resolution is generally achieved when a higher-resolution model is nested within a coarser
model. The measured current profile data (deliverable C) should be used to validate and/
or calibrate the hydrodynamic model (deliverable D of Figure 5). There are several freely
available ocean current datasets:
• Copernicus Marine Environment Monitoring Service (CMEMS), https://marine.
copernicus.eu/
• Plymouth Marine laboratory: data portals, https://portal.ecosystem-modelling.pml.
ac.uk/
• HYCOM (consortium for data assimilative monitoring), https://www.hycom.org/
3.1.3.5 CO2 dispersion model (biogeochemical model)
The hydrodynamic model needs to be coupled with a biogeochemical model, which includes
descriptions of carbonate chemistry and the bio-physical processes that influence the
carbonate system. With minimal development and suitable evaluation against real-world
data, these models can produce high frequency representative time series of observable
parameters such as pH and pCO2, and co-variables such as O2 and nutrients, potentially
at intervals of a few minutes over seasonal and decadal time scales. Model outputs of
33
Seabed and overburden integrity monitoring for offshore CO2 storage
the above-mentioned parameters are typically saved at daily time intervals (for example
daily mean values) per grid point (deliverable E of Figure 5). However, model time steps
are usually of the order of a few minutes to sub-hourly, so high frequency data can be
generated, which may be a requirement during a leakage. It should be noted that model
outputs of these parameters in some cases show less small-scale variability than the
real data, due to the necessary aggregation of processes, water volumes and species into
functional groups. In other cases, the models are not too far short of picking up the smallscale variability.
3.1.3.6 Perform model test runs and sensitivity studies of the model
Only a few marine CO2 release experiments have been undertaken. They are restricted to
specific locations, limited time frames and small volumes of CO2. However, they do enable
the evaluation of multiple model test runs (deliverable F of Figure 4), which provide an
ability to detail spatial-temporal CO2 baselines and simulate diverse scenarios of leakage,
and the variability in hydrodynamic conditions during a year (e.g., degree of stratification
of the water column). The coupled models should be validated and calibrated with
observational data, as much as possible. Properly evaluated model systems can provide
characterization of natural chemical variability, contributing to baseline assessments
and the identification of anomaly criteria in terms of changes of pH as a function of time,
distance from the release point, the magnitude and duration of the CO2 release.
3.1.3.7 Maintain and run the combined (hydrodynamic and biogeochemical) model
during accidental release of CO2
This deliverable (G of Figure 5) is the result of the model developed in Figure 5 under
deliverables D and E and tested under deliverable F. Such simulations would help
characterize the extent of impact of the CO2 release especially in parts of the area of
interest not well covered by sensors.
3.1.3.8 Impact assessment of CO2 leak on water properties and biological
communities
Coupled marine systems models are expected to be consistent with observations for
physical and chemical constituents (e.g., temperature or nitrate concentration), but they
are less suitable for evaluation of biological components because such models lack detail
in terms of biodiversity and the parameterization of biological impacts arising from excess
CO2. In addition, small errors in physical or chemical predictions are often amplified by
dependent biological process descriptions. In other words: models will not provide direct
assessments of ecosystem damage but can provide indicators of impact extent and are a
good tool to study various scenarios and sensitivities (deliverable H of Figure 5).
An assessment of the potential ecosystem damage could comprise the following elements:
• Impact on calcium carbonate (CaCO3) reliant organisms
• Effects on benthic fauna (corals, crustaceans, mollusks, and echinoderms)
• Effects on multi-cellular organisms and fish
• Effects on sediment-dwelling and benthic (bottom dwelling) organisms
• Effects on bacteria, nanobenthos, and meiobenthos
34
Seabed and overburden integrity monitoring for offshore CO2 storage
3.2
Monitoring methods
Near-surface monitoring methodologies use permanent installations providing continuous
monitoring in high-risk areas, such as injection sites, outcroppings, and old or abandoned
infrastructure. The wide area of the store, which has a much lower risk profile, then has
periodic monitoring from mobile assets. The technologies to achieve this are examined first
then the concepts of operation are explored in more detail (deliverable I of Figure 5).
3.2.1 Acquisition platforms
A platform should be suitably matched to its sensor payload. While there is often a great
deal of interest in sensor platforms, such as AUV, they are simply a delivery mechanism for
their sensors and their primary design and operational driver are the requirements of their
payload. Other platform key selection criteria include:
• Acquisition cost
• Spatial/endurance capabilities
• Safety of launch and recovery of the system
This section examines the main criteria that various platforms offer to enable
data collection.
3.2.1.1 Static installations
The instrumentation on injection apparatus and downhole monitoring equipment
will naturally form part of the continuous monitoring of the injection site. This may
be supplemented using additional stationary platforms to provide permanent close
observation of high-risk areas. These platforms are most likely to be in the form of landers
deployed to the seabed (e.g., chemical sensors, pressure monitoring transponders,
gravimeters, tiltmeters/inclinometers…). Static landers provide many advantages:
• Constant presence
• High in-service time – may require annual or bi-annual servicing
• Can take a high battery payload to power energy intensive systems such as
active sonars
• If they are close to other infrastructure may be able to connect into subsea power and
ability to provide live feeds via acoustic or hardwire communication networks
• Power and size capacity to support large sensor arrays and onboard processing
• Large size can support chemical sensors requiring the storage of reagent bags
• Sensors can be accurately placed at an optimum height above the seabed
• As they are static, they can integrate data over long periods to get more sensitive or
accurate results
Positioning is critical with static landers. As a platform for chemical sensors, they should
be positioned relative to the high-risk location, so that if there is a leak, the prevailing tidal
and current conditions may carry the CO2 plume towards the lander. They should then be
close enough to ensure that there is a suitable concentration of detectable substance so
that a problematic leak can be identified in a timely manner.
35
Seabed and overburden integrity monitoring for offshore CO2 storage
A method of communicating with the lander should be established. If there is suitable
nearby infrastructure, a wired solution may be possible. This gives robust and high data
rate communications. If there is no suitable connection point in the vicinity, a wireless
solution via a gateway buoy or USV would be required. For areas with a high amount of
trawler fishing, trawl resistance should be considered. No design can be completely trawl
resistant, but designs can be made more resilient to glancing blows. Static landers will also
carry a high maintenance overhead. They will need periodic maintenance approximately
every one to two years for sensor calibrations, cleaning, battery changes, restocking
chemical agents, and changing reagent bags. Given the size of these landers will likely be
greater than 500 kg, recovery will be a significant task.
3.2.1.2 Mobile platforms
The diversity of mobile platforms has increased over the last decade, largely driven by
the growing capability and adoption of autonomy. This section will examine the various
advantages and disadvantages for the vehicles that may be considered. Payload, cost,
operational range (which may tie in with sensor power requirements), and safety (during
launch and recovery) are key factors to be considered.
3.2.1.2.1 Autonomous Underwater Vehicles (AUVs)
Autonomous Underwater Vehicles are uncrewed submarines that are usually deployed from
a larger vessel. Newer, long-range variants trade depth capability for extra battery capacity
and can be deployed from shore. As they have conventional steering and propulsion, they
can execute a survey plan accurately, while active depth control allows them to cruise at
a height above the seabed for optimum sensor performance. The size of AUVs varies from
hand portable systems to that of 10-15m long.
AUVs have been used in the oil and gas industries for more than two decades, mainly for
geophysical survey (with MBES, SSS,SBP profiler and more recently camera/video) or
inspection survey (laser, stills camera, MBES, SSS). Such applications are fully relevant
for near-surface offshore CO2 storage baseline and monitoring. In addition, under
development, chemical sensors (pCO2, pH) may be deployed.
3.2.1.2.2 Autonomous Surface Vehicles (ASVs)
Autonomous Surface Vehicles (also called Uncrewed (or Unmanned) Surface Vessels –
USVs) are uncrewed vessels that operate on the sea surface, generally 3-10 metres long to
enable easy transport. They are rarely truly autonomous and rely on a data link to shore for
conduct. Their main advantages over conventional vessels are the reduction in emissions,
cost, and HSE exposure. As CCUS storage sites will be relatively near shore, deployment
from harbour is a practical option.
The discussion around their use is similar to the AUVs with the clear differentiation that all
their operations will be on the surface. Many have solar panels to supplement batteries and
some of the larger ones will also have small generators. They will be suitable for mounting
active sonars, but vessel self-noise and surface noise would make operation of passive
sonars impractical.
36
Seabed and overburden integrity monitoring for offshore CO2 storage
They have a greater energy capacity and navigational accuracy compared with AUVs,
resulting in a more comprehensive sensor suite and range. On the other hand, ASVs are
influenced by surface weather, wave heights and currents etc, and are thus a less stable
platform than AUV’s. As the sensor suite will be at the surface, it will not have the ability
to be deployed at an optimum height above the seabed for detection. Some AUVs offer the
ability to deploy towed arrays, which is a useful feature, but these arrays will not be able to
have the sensor payload of a AUV or towed array from a conventional vessel. Some ASVs
may serve as support vessel for AUVs and ROVs.
3.2.1.2.3 Subsurface gliders
Subsurface gliders (not to be confused with wave gliders) are small buoyancy-driven
autonomous underwater vehicles and a widely-used modern oceanographic tool. They are,
typically, about 200cm in length and weigh around fifty kilograms. Gliders cycle up and
down through the water column in a saw tooth pattern. Once at surface, buoyancy tanks
are filled causing them to descend through the water as wings propel them forward. At the
bottom of this decent, the tanks are emptied, and the glider starts to climb with the wings
again providing thrust as the glider moves upwards through the water.
This is a very efficient method and very long endurances are achievable. Deployments of
about a year are now possible, with deployments of 3–6months now routine, and survey
tracks extending over 1,000s kilometers.
If no other system is used (absence of boat or autonomous surface vehicle), the underwater
positioning will rely only on the glider dead reckoning algorithm with lack of positional
accuracy and optimum positioning above the seabed for sensors. The propulsion is largely
unable to make headway against strong depth average currents. Glider manufacturers and
users have implemented a wide range of sensors on the platform and various physical (e.g.,
pressure, salinity, currents) biogeochemical (e.g., pCO2, O2, pH) and acoustic parameters
(e.g., hydrophones, echo sounder) can be recorded, many of them accessible in near
real time.
They would fit in a concept of operations where they are deployed for extended periods to
collect baseline data and monitor temporal changes in parameters over long durations, or
due to their low cost deploying many platforms to get suitable coverage, including
leak monitoring.
3.2.1.2.4 Remotely Operated Vehicles (ROVs)
Remotely Operated Vehicles are platforms deployed from a crewed or more recently,
uncrewed vessel, able to move in high degrees of accuracy in three dimensions. They are
controlled by an operator onboard the support vessel (crewed) or remote-control centre
(uncrewed). They vary in size from hand portable nearshore and shallow water ROVs to
very large offshore deep-water intervention (work class) ROVs, with dedicated launch and
recovery system and and high payload capability. For CCUS applications, typically they
will be towards the larger end of this range, capable of carrying all required equipment.
An ROV has a continuous power supply from the vessel and can carry power intensive
payloads. Due to the tether to a large vessel and slow transit speeds, typically these would
not be for monitoring a large area, but for more detailed inspection and intervention.
37
Seabed and overburden integrity monitoring for offshore CO2 storage
As ROVs can be positioned with a high degree of accuracy, they are excellent platforms
for collecting visual data and very precise chemical sampling. The use of ROVs is most
likely to be part of a follow-up investigation in which precise location, measurement, and
investigation over a tightly defined area is required, such as anomaly detection.
3.2.1.2.5 Conventional vessels
Crewed service vessels are still the main delivery mechanism for offshore services globally.
Their practices are well established, and generally they are widely available. To carry a
suitable sensor payload, to the areas we would expect CCUS to be undertaken, for several
days at sea, vessels will likely by longer than 30 meters.
They combine the advantages of many of the other platforms and provide some
additional advantages:
• High positioning accuracy
• Large size and power capacity for complex sensor suits
• Ability to deploy towed arrays to place sensors at optimum depths
• Onboard ROVS for searching large areas
Onboard staff for rapid data interpretation, sample management, time-critical testing, and
programme decision making
Activities for CCUS monitoring are not high risk and the actual exposure is not likely to
be significantly more than the cranage and deployment of unmanned vessels from shore.
Conventional vessels primary limitation is cost, and increasingly, carbon footprint. They
are expensive, with relatively high day rates compared with uncrewed vehicles, higher
mobilisation rates and more shoreside support overheads. There can also be savings found
in mobilising them for multiple tasks at once, as they can carry several mission payloads
simultaneously – if a suitable vessel asset is in area, then large common costs (such as
mobilisation, transit, weather time) can be spread between projects.
3.2.1.2.6 Ships of Opportunity (SOO)
Ships of opportunity are vessels that are not primarily tasked with monitoring operations.
For example, field support vessels’ (FSVs) or Platform Supply Vessels (PSVs) for O&G field
operations. There are systems that can be fitted to monitor oceanographic parameters,
including seawater composition, along the route. This would not provide sufficient data or
methodology for core monitoring activities, so they are not included in that discussion, but
may for part of a consideration for monitoring baseline drift.
3.2.1.2.7 Acquisition platform comparison
While the above sections have given some indication of the likely employment of
different platforms, mobile platforms are subject to different sensor requirements,
evolving technology, site specific factors and changeable cost models. Table 3 provides a
comparison of these factors. Scores assigned are relative to each other and do not account
for project specific requirements or weighted operator preferences.
38
Seabed and overburden integrity monitoring for offshore CO2 storage
Range
Mission Payload
Onboard processing
Navigation - Accuracy
Navigation - Positioning
Sensor position (depth)
Cost
Re-tasking*
Criteria
AUVs
3
3
3
3
3
5
4
4
ASVs – active power
4
4
3
5
4
3
4
4
ASVs – passive power
5
3
2
5
2
2
4
2
Criteria
Platform
Subsurface gliders
5
2
1
3
1
2
5
0
ROVs
1
4
1
5
5
5
2
5
Conventional Vessels
4
5
5
5
5
4
2
5
Table 3: Acquisition platform selection matrix. 0 – No capability, 1 – Low, 2 – Below average,
3 – Satisfactory, 4 – Good, 5 - Excellent
Both AUVs and ASVs can revisit areas of interest if an anomaly is detected to collect more
data, conventional vessels can carry a large mission payload, such as an ROV to conduct
more in depth investigations.
3.2.2 Acquisition sensors (geophysics, hydroacoustic, geochemistry,
biological)
The sensor suite deployed to provide monitoring is part of a complex trade-off between
the legislative requirements, what is technically possible from both the performance of
the sensors and platform, and cost. These interactions will be highly project specific. This
section gives an overview of the capabilities that different sensors provide, some of the key
factors to consider for use, and matching with platforms.
3.2.2.1 Chemical sensors
Chemical sensors can be mounted to static and mobile platforms. When mounting to
mobile platforms, the first aspect to consider is the sampling and processing time of the
sensor. This needs to be suitably fast so that the sensor can sample at a suitable frequency
relative to the vehicles speed through the water. Chemical sensors then need to be
matched to the available power and space on a mobile platform. Considerations for space
may also include the requirement to store reagent bags which cannot be released to the
environment. These concerns are much simpler on static and mobile crewed platforms,
with far less complexity over movement and, in comparison to autonomous vehicles, more
space and power.
Part of the discussion around chemical sensors for a project should also examine the use
of sediment sampling. This is unlikely to be for in-situ analysis or uncrewed vessel systems
39
Seabed and overburden integrity monitoring for offshore CO2 storage
but sampling for laboratory assessment. This methodology may go some way to mitigating
the complexities caused by the environmental and hydrodynamic effects. Research and
development projects did show a marked increase in concentration at the sediment-water
interface (as opposed to higher in the water column), which would improve detectability.
Carbonate system
The carbonate system, to indicate the presence of CO2, of the water column can be
measured on factors of Dissolved Inorganic Carbon (DIC), dissolved CO2 (ρCO2), Total
Alkalinity (TA) and pH. Measuring DIC and ρCO2 is currently considered impractical due
to the very low chemical signal that both these parameters will give in a hydrodynamic
environment and hence very short detection ranges. For this reason, pH is often the most
practical to measure. It offers the best likelihood of detection and there are readily available
seawater pH sensors. Commercially available sensors have an accuracy of 0.01pH, which is
sufficient for detection. For leak rates of less than 1 tonne per day, then the dominant effect
is limited to less than 3m from the seabed and may not be suitable for AUV deployment due
to flight height restrictions.
Figure 6: Estimated detection length scales for the range of leakage scenarios
(Blackford et al, 2020)
Due to the damaging nature of release experiments at representative rates, detection
range research has been largely limited to modelled examples. Figure 6 indicates that a
leak of 1Kg/d would require a sensor within a one meter radius, a one tonne per day (T/d)
leak could be detectable at around 60 m distant, and a one metric tonne per day (M T/d)
leak at 7.8 km distance. As no more than 1% of stored CO2 can be released to maintain
an acceptable degree of storage integrity (IPCC, 2005) and using the Sleipner injection
rate as an example, then a release of 30 T/d would be detectable at approximately 660 m
distance.13 Caution should be applied to these modelled results. Due to the impracticality
of conducting such large-scale releases of CO2, there is no experimental evidence to
support the top end of this scale.
13
Blackford J et al, 2020
40
Seabed and overburden integrity monitoring for offshore CO2 storage
Release experiments that have simulated approximately 100 kg per day have shown far
more modest performance than modelling suggests, with detections only made very close
to the source.
pH sensors are not energy intensive and lend themselves well to deployment on batteries.
They do suffer from drift, so for protracted deployments, such as on a lander a method
of correcting or calibrating this drift should be considered. To correct pH (and DO) both
temperature and salinity should both be measured, as they are dependent variables.
Verification and attribution
Chemical sensors for verifying and attributing the source of any anomalies fall into two
broad categories:
• Ensuring that perturbations in chemical profiles are not due to biological activity
• Detecting tracer elements that will indicate the operator of the leaking store, which
can aid initial detection
To determine the impact of biological activity, refer to the sensors proposed in Table 3:
Content of a typical baseline study, where dissolved oxygen (DO), nitrates, and phosphates
are measured. While only one of these parameters needs to be measured to determine
whether a pH anomaly is biogenic, it may be desirable to include all three on a platform
such as lander. This gives increased data and redundancy where there is platform capacity,
for little increase in cost. Sensors for these parameters are commercially available, but
not as widely as pH sensors. Many research institutions have their own sensors developed
in-house for these parameters, which may not be at a commercial Technology Readiness
Level, but may be worth exploring as high accuracy alternatives.
The inclusion of tracer elements into the sequestered CO2 is not yet confirmed as
standard practice. Suitable tracer elements that have been identified are helium and
xenon isotopes (particularly 124,129Xe), and artificial tracers such as perfluorochemicals
(PFCs) and deuterated methane14. Studies into this methodology have reservations about
the performance of tracer elements as they migrate through the shallow overburden
and potency over time. Given the uncertainties of this approach, development of suitable
sensors has been limited.
3.2.2.2 Acoustic sensors
Acoustic sensors fall into two main categories. Active acoustic, which transmits
soundwaves and builds a picture from the reflected energy and passive acoustic, which
does not transmit but ‘listens’ to determine what is happening in its vicinity. In offshore CO2
storage applications, acoustic sensors can be used to provide near photorealistic imagery
of the seabed, which can be used to visually identify gaseous leaks. This imaging can also
be used to identify leak features in the sediment, such as pockmarks. They can also take
highly accurate bathymetric readings to monitor changes and anomalies in the seabed
indicative of leaks or containment issues lower in the shallow overburden. Passive acoustic
sensors are overall less capable but come with advantages that will be discussed later
in this section. Their primary application is to ‘listen’ out for the frequencies that would
indicate a leak or other anomalous event.
14
Roberts et al, 2017
41
Seabed and overburden integrity monitoring for offshore CO2 storage
Active leak detection sonars can be mounted on static landers around high-risk areas of
leakage. These function by inducing vibration in the individual bubbles of gaseous phase
bubble plumes, increasing the return signal over that which may not have been detectable
via passive methods. These sonars can also be used in noisy environments, such as near
the injection site where there will be lots of plant noise, where passive sonars would be
unable to discern events.
Active sonars in the forms of Side Scan Sonar (SSS) and Multi-Beam Echo Sounder (MBES)
provide high resolution imagery of the seabed and objects in the water column, such as
bubble plumes. This can be coupled with an automatic target recognition algorithm, which
can highlight bubble plumes from seabed seeps to improve detection capability.
It should be noted that both systems need a stable platform, such as a submerged
AUV, ROV, or actively stabilized surface vessel. Imagery from them can be smoothed via
processing although this may lead to the omission of important data. MBES are slightly
more robust to this movement. All these forms of active sonars are in widespread
operational use and would require minimal platform integration.
Passive sonars are at a lower technology readiness level with less demonstrable operation.
They however provide a lower power monitoring solution than active sonars for high-risk
locations of a CO2 storage that could be located some way from the injection point, such as
legacy wells. They have a higher sensitivity than active sonars, as they can integrate data
over a time period, but this also heightens their susceptibility to noise.
3.2.2.3 Deployment of sensors
In the preceding sections the capabilities of the platforms and the sensors have been
examined. This needs to be applied to the MMV principles discussed at the start of Section
1, and considered with both engineering and operational judgement.
The MMV principles from Section 1.1.1 provide containment, conformance, and confidence
for shallow-focused monitoring, capable of detecting and quantifying near-surface
emissions likely to pose a health and safety threat or environmental impact. Shallowfocused monitoring relies upon near surface monitoring technologies generally developed
and implemented by marine geoscientists, oceanographers, and environmental scientists.
Conformance with modelled behaviour is the domain of deep monitoring to ensure that the
injected gas is migrating through the storage complex as expected. Deep monitoring can
also assure containment and provide confidence of the deep containment mechanisms,
with shallow monitoring providing measurable indications that deep monitoring is indeed
correct and the environment is not suffering any damage.
Acoustic detection of gaseous phase bubbles is the most obvious indication of leakages.
The supercritical CO2 of the store will go through complex phase changes to reach the
seabed. While this is happening, it will be translating laterally, diffusing and eventually
dissolving with saturated sediment. Suitable site characterization should identify any
pathways, but that is not to say one may not have been found or some fault may develop in
either the natural containment or sealing of old wells. Pockmark detection should in some
way mitigate this uncertainty as it can detect fluxes in both different phases, which may
include precursor brine.
42
Seabed and overburden integrity monitoring for offshore CO2 storage
Chemical detection also has a high degree of uncertainty. The natural variability and
reactions to the introduction of CO2 mask emissions. While modelled results provide
encouraging theoretical detection ranges, experimental findings are more modest.
Chemical detection relies on a leak establishing itself for a period to get the necessary
detectable concentrations, which does not lend itself to rapid responses.
Shallow monitoring techniques, especially over a wide area, are not in themselves a
full solution for containment or confidence. It is not the intent to suggest that shallow
monitoring may be unfit for purpose; however, incorrectly delivered shallow monitoring
could provide no meaningful results, including false positives or negatives, and as such
affect the environment, reputation, cost, and timelines. An integrated deep and shallow
monitoring strategy across development phases, where context and layered data is
analysed to provide a true picture, provides the best opportunity for success. Shallow
monitoring techniques should be considered to have quantification capability, as in the
event of a leak, this techniques could support leak volume assessments.
3.2.3 Example missions and surveys
3.2.3.1 Capability matrix
The matrices describe the capabilities examined in this document. There will be other
monitoring methods (such as downhole monitoring) but the purpose of this section is to
examine interaction between deep and shallow monitoring and the potential for overlapping
capabilities. The project phases are: Phase 1 – Assessment, Phase 2 – Characterization,
Phase 3 – Development, Phase 4 – Operation, Phase 5 - Post-Closure/Pre-Transfer, Phase
6 - Post Transfer. The activities for Phases 5 and 6 are similar to previous phases in terms
of methodology. The periodicity may change to reflect the decreased risk and the objective
would be more focussed on confidence with the intention to transfer liabilities.
Table 7: Phase 2, 3, and 4 (characterization, development and operation) monitoring
techniques
Objective
Objective
description
Deep/
shallow
Output
Sensor
requirements
Platform
Discussion
Phase 2 and 3 - Characterization and Development
Containment
Integrity of
complex
containment
mechanisms
Deep
Seismic data,
identification of
routes to surface
from storage
complex
Seismic
towed array
Large
Vessel
Confidence
Identification
of natural
fluxes to avoid
confusion with
induced fluxes
Shallow
Geomorphology,
bathymetry, water
column imaging
(gas plumes),
near surface
geology
SSS/MBES/
SBP/UHRS
Surface
vessel
AUV,ASV,
ROV
43
Wide area
coverage of
primary flux
identification
indicators
Baseline
bathymetry
to detect
anomalous
movement
Seabed and overburden integrity monitoring for offshore CO2 storage
Objective
Objective
description
Deep/
shallow
Output
Sensor
requirements
Platform
Discussion
Confidence
Identification
of chemical
baseline to
monitor and
measure
anomalies
against
Shallow
Annual profile of
key measurement
parameters,
several years of
data would also
give range
Carbonate
system
Lander
Monitoring of
the key points
of the storage
complex
in order
to identify
anomalies
and baseline
conditions
in order to
detect and
quantify
leaks.
Understand
the
hydrodynamic
environment
and how the
dispersal
of leaked
hydrogen may
evolve
Shallow
Tidal and current
conditions at site
ADCP
Lander
Seismic array
Large
Vessel
Conformance
Attribution
parameters
Phase 4, Operation
Containment
Conformance
Identify
breaches
of primary
(or later)
containment
mechanisms
Deep
Identify
extent of CO2
migration
through
the storage
complex
to confirm
modelled
behaviours
Deep
Seismic data
OBNs
Seismic data
44
Seismic array
Large
Vessel
OBNs
A study
would need
to be made
as to the
preference of
towed arrays
over OBNs,
noting the
potential
interference
of other
users, such
as windfarms.
Same data as
previous item
with different
objective
Seabed and overburden integrity monitoring for offshore CO2 storage
Objective
Objective
description
Deep/
shallow
Output
Sensor
requirements
Platform
Discussion
Confidence
Identify
extent of CO2
migration
through
the storage
complex to
confirm stored
volume
Deep
Seismic data
Seismic array
Large
Vessel
OBNs
Same data as
previous item
with different
objective
Containment
Provide
monitoring
at high-risk
locations
Shallow
Alarm if there
is a detection of
trigger factors
Leak
detection
sonar
Chemical
monitoring of
conditions
Lander
Constant
presence
at high-risk
locations
Shallow
Alarm if there
is a detection of
trigger factors
SSS/MBES
Chemical
suite
Surface
vessel
This
methodology
may also
include
sediment
sampling
Improve
understanding
of
environmental
trends
Containment
Monitor areal
store
AUV
ASV
Containment
Monitor areal
store
Shallow
Bathymetric
data to confirm
overburden
performance and
integrity
MBES
Seafloor
deformation
monitoring
instruments
(pressure
sensors)
Surface
vessel
AUV
SUV
This
methodology
is used at
Sleipner and
Machar
Lander
3.2.3.2 Concepts of operation
All monitoring concepts for offshore storage complexes provide a risk-based approach.
While it is technically feasible to have static landers providing constant shallow monitoring
over the entire storage complex, this would not be cost effective, nor is it required. From
the approaches examined in Section 3.2.3.1, there are overlapping capabilities which
can be traded-off against each other, combined with the likelihood of areal leakage from
the primary containment being extremely small. While this does intuitively push for a
minimalist approach to monitoring, the strategy should be suitable for the risk profile of the
store and provide meaningful evidence of absence of any leaks. These design factors will be
examined more fully, with other requirement drivers such as regulatory requirements,
in Section 3.4.
45
Seabed and overburden integrity monitoring for offshore CO2 storage
Using these broad principles, an outline concept of operation would be:
Phase 1 – Assessment: This is a desk study phase where the monitoring philosophy
should be established, and major characteristics identified from extant information. These
characteristics can then have an outline monitoring strategy defined, or they may preclude
the suitability of the site for CO2 storage.
Phase 2 – Characterization: The characterization phase is to develop the outline of the
storage feasibility put forward in the assessment without committing to the full-scale
development phase costs. This would likely focus on deep monitoring with the aim of
identifying of yet unfound leakage routes. Given the range of natural variability in chemical
parameters and the relative cost of a measurement campaign, it would be prudent at this
time to deploy landers to understand the marine and hydrodynamic environment.
Phase 3 – Development: Once the development phase is underway, there is greater
certainty over future investment. At this stage if it has not already been started, the
chemical environmental baseline campaign should be started. The areal extent of the store
should then be baselined for shallow leak identifiers, such as pockmarks, and to establish
the baseline bathymetry.
Phase 4 – Operation: During the operational phase, the site operator should comply fully
with the regulatory requirements, which will likely be the primary requirement driver.
The risk-based approach to this will be constant surveillance at the high-risk areas using
landers, with periodic wide area surveys using the methods discussed in section 3.2.
Landers will then relay their data in real time to an operations centre. In most cases these
wide area surveys would be cheapest utilising suitably instrumented AUVs. Data from
surveys can then be transmitted live for preliminary analysis (on board, in the case of large
vessels), or stored onboard for later analysis. This latter approach caries risk of slowing a
reaction to anomalies detected and prevents re-tasking (see Section 3.2.4). The periodicity
of the wide area surveys will be driven by the risk profile of the store and regulatory
requirements for complex wide water column monitoring. When examining overlapping
capabilities, we can see there are multiple ways of demonstrating containment. It will be a
trade-off on cost effective and compliant methodologies adopted by the operator.
Phase 5 - Post-closure/pre-transfer: Following the end of injection operations, the
monitoring regime will be defined by the jurisdiction’s regulatory requirements. It
logically follows that the monitoring regime will be the same as that employed during the
Operational phase but at a reduced periodicity to recognise the reduced risk as there is no
active injection.
Phase 6 – Post-transfer: With the liabilities transferred to the national body, shallow
monitoring will be driven by the risk profile of the store and may not be required. Deep
monitoring would need to continue if the CO2 plume has not yet stabilised and continues
to migrate in a way that may be problematic. Shallow monitoring may be combined into an
academic exercise in the local ecology.
46
Seabed and overburden integrity monitoring for offshore CO2 storage
3.2.3.3 Example missions
For the key technologies (landers and AUVs) discussed for Phase 4 operational monitoring,
it is possible to give example missions. The shallow monitoring discussion is not weighted
towards any specific technologies and/or parameters, because many variables play a part
in defining the correct solution for a particular site. However, the combination of landers
and AUVs is widely considered as a recommended solution.
Landers will be deployed in the vicinity of high-risk features, such as the injection site,
old and abandoned infrastructure, and natural leakage pathways. The sensor outfit for
a lander will likely consist of a leak detection sonar and chemical suit. They should be
situated so that the hydrodynamic conditions move chemical leakage effects towards them.
There should be continuity throughout Phases 3-5 over the lander siting and measured
parameters. From deployment, there will be a regular maintenance regime to ensure the
lander’s continued effectiveness. This will consist of cleaning to remove marine growth and
debris, replacing batteries, calibrating and maintaining instruments, and replacing reagent
bags. Using a standard maintenance cycle for marine deployed instruments would put this
activity as every one to two years. It may seem an attractive solution to try and increase the
endurance of a lander by supplying surface power, which may be possible with fixed cabling
in the vicinity of infrastructure but has a poor reliability record when flexible cabling is used
from a buoy. Landers will need a form of gateway to return their data. As with power in the
vicinity of fixed infrastructure, a cabled link may be possible, which would enable very high
data rates. If this is not possible, there will need to be a surface gateway, either in the form
of an ASV or buoy. The wireless communications between the lander and buoy will have
less bandwidth than a wired link and may lead to the requirement for onboard processing
for data compression.
In addition to the permanent but localized monitoring provided by the landers, AUVs will
provide a periodic and spatial assessment of the CO2 storage area and aa prudent estimate
would put this periodicity at every three to five years. AUVs would be equipped with a SSS
and/or MBES and/or SBP and a light chemical suit capable of rapid processing sampled
water as the AUV moves. The flight height of the AUV would need to be tailored to allow
greatest coverage of the SSS/MBES but may also be adapted to sample gas bubble close
to the seafloor. The AUV would run reciprocating adjacent survey lines over the storage
complex, this is most efficiently done moving with and against prevailing tidal and
current conditions.
3.2.4 Data management, processing
Large amounts of data will be produced by the monitoring operation from disparate
sources and will require careful integration. Handling of the data will be crucial to leading
effective decision making. For this to be the case there will always be a human involved,
but their efficiency and error rate can be improved with the aid of automation and userfriendly displays. Data displays have been discussed at length in the section on GIS in this
document. (Section 3.1.1)
Where automation can greatly assist is in highlighting areas of concern to a human
operator. This at first happens in bandwidth restricted areas. Examples of this would be
on a wide area survey. When surfacing, an AUV has a limited amount of time to transmit
its data. By identifying data of interest through an Automatic Target Recognition (ATR)
algorithm from onboard processing, in both chemical and sonar, it allows shorter and
47
Seabed and overburden integrity monitoring for offshore CO2 storage
hence cheaper data transmission. For the shoreside operator it then allows a more efficient
data sift where ATR false positives can be quickly discarded. If a conventional surface vessel
is used and data is being manually examined as it is collected an effective ATR also reduces
operator fatigue, and hence, likelihood of error. For static landers the constant data stream
will need an alarm feature as constant monitoring of sufficient vigilance is simply
not possible.
As discussed in Section 2.2.7, absolute thresholds to detect anomalies in the carbonate
system are not sufficient due to the variability and range pH, which is the most likely
parameter monitored. Using the performance of chemical sensors and modelled
detections examined in Section 3.2.2.1, a change in the data of 0.01pH would be a flag for
further investigation.
Data may need to be re-examined for several reasons including missed detections. For
liability and good practice, the full set of data should be retained in line with regulatory and
company policy. This data archive may also prove useful in developing machine learning to
identify leaks more effectively.
3.3
Value of information
Shallow monitoring data will be of low value without context. This puts a significant
burden on the need to have good store characterization. A shallow monitoring anomaly
detection will be of low value, in the sense it will be a high probability of false-positive or
unattributable to a leak mechanism, unless is correlates with a suitable geological feature.
This weights early data collection in favour of deep monitoring techniques. Shallow
monitoring is of far greater importance during operation as the ability to meaningfully
quantify any emissions and qualify their environmental impact will be a key capability
that regulatory bodies will require. This extends the requirement for robust near-surface
baselining in development phases.
It is extremely difficult to attribute a weighting to any shallow monitoring technique, that
chemical detections may be better than acoustic or vice-versa. Data will have far more
cumulative value when considered together and as such handling and display systems
should consider this layering feature as a high priority requirement.
3.4
Workflow decision diagram (to help operators make
appropriate choices)
This section examines the major processes in the workflow of through-life monitoring
of a CO2 storage site. These are aligned with the major operational steps and common
regulatory requirements in a site development, but regional and operator variations will
apply. Phase 3, development, presents complexities as until this point there is limited
certainty over the project and major investment will not be released prior to this. Expensive
activities, like seismic acquisition, will need to be initiated and the results implemented
within this phase. As such the workflow diagram here shows the major process of this
phase as a two stage activity. Savings in time and cost may be made where there will legacy
data available for depleted oil and gas fields, which may slightly influence the order and
content of this process.
48
Seabed and overburden integrity monitoring for offshore CO2 storage
Phase 1: Assessment
Site characteristics/Risk
identification from extant
information
Regulatory monitoring
requirements
Licensing requirements
Identify general monitorability of storage site and complex.
Identify project feasibility.
Concept - License
Feasibility of store
Outline monitoring plan
Phase 2: Characterization
FEED
CO2 migration
modelling
Corporate safety
guidelines
Concept study
Perform storage containment/IS risk assessment. Based on this
assessment, design MMV plan and corrective measures plan
Baseline campaign plan (may
even initiate)
Through life MMV plan for
development and operation
and supply chain
EIA proposal
Identify relevant background data
Report on major hazards
Phase 3: Development
Technology trade-off
study
FEED study
Storage Characterization
Background data
Acquire baseline monitoring data
Initiate EIA
Initiate shallow baseline
measurements
Finalise storage technology feasibility studies
Acquire seismic data
Internal emergency response
plan
Finalised MMV plan
49
Seabed and overburden integrity monitoring for offshore CO2 storage
Phase 4: Operation
Finalized MMV Plan
Monitoring plan revisions
Store characterization
Monitoring results
Anomaly response
Regulatory required reporting
Operational MMV. Acquire planned monitoring data
(base monitoring plan) and history match dynamic models; update as
necessary.
Internal safety reporting
Finalized closure MMV plan
Phase 5: Post-closure/pre-transfer
Closure MMV Plan
Risk assessment updates and additional monitoring
as required to prepare handover to government.
Demonstrate long-term containment and
conformance with subsurface models.
Acquire seismic data,
demonstrate stability in plume
Final shallow monitoring results,
demonstrate EIA compliance
Handover documentation
Phase 6: Post-transfer
Handover documentation
Jurisdiction continued
monitoring plan
Monitoring as indicated by updated risk profile of
storage site containment and conformance with
subsurface models required.
Release of public domain data
Figure 7: Workflow decision diagram
50
Data acquisition as required
Seabed and overburden integrity monitoring for offshore CO2 storage
Appendix A: Review of regulatory
frameworks and standards relevant to
seabed and overburden integrity
There are several regulatory requirements relevant to seabed and overburden integrity
which are addressed in international, regional, and country-specific regulations. Examples
of these regulations and extracts from them relating to seabed and overburden integrity are
provided in this Appendix.
A.1. International Regulations
A.1.1 The London Protocol
The London Protocol (1996), under the London Convention (Convention on the Prevention
of Marine Pollution by Dumping of Wastes and Other Matter, 1972), regulates the disposal
of wastes and other matter at sea. Under the Protocol all dumping is prohibited, apart
from eight types of wastes listed in Annex I of the Protocol and for which a permit way be
delivered by the National Authority. In 2006, the London Protocol was amended to add subseabed geological storage of CO2 in Annex I.
London Protocol Risk Assessment and Management Framework for CS-SSGS (RAMF) and
associated Specific Guidelines for the Assessment of Carbon Dioxide for Disposal into Subseabed Geological Formations (the 2012 Guidelines) recommend:
• Environmental baseline data is required to assess the pre-existing level of exposures
of organisms to natural hazardous substances and ubiquitous contaminants that may
be released due to the injection and the effect of additional exposure (Article 7.4).
• Environmental baseline data is required to identify sensitive ecosystems or species,
sensitive areas and habitats, other amenities or uses of the sea (Article 7.5).
• Near-surface baseline data is required such that changes that arise due to
sequestration of carbon dioxide streams can be monitored (Article 8.4).
• Monitoring of the seafloor and marine communities may be included in the
monitoring program (Article 8.9), but this monitoring could be part of the contingency
plan (RAMF, s.6.22).
A.1.2 The OSPAR convention:
The OSPAR Convention (Convention for the Protection of the Marine Environment of the
North-East Atlantic, 1992) is the main legal framework governing the protection of the
marine environment in the Northeast Atlantic and North Sea. The EU (initially as the
European Community) and 15 individual states (mainly EU Member States) are Contracting
Parties to the Convention. Since 2007, OSPAR member countries have been allowing subseabed geological storage of CO2, provided the contracting parties apply the OSPAR FRAM
Guidelines when granting permits or approvals by the competent authorities. In details for
CO2 subsea storage, the following documents should be considered:
• Decision 2007/2 on the Storage of Carbon Dioxide Streams in Geological Formations.
• Framework for Risk Assessment and Management of Storage of CO2 Streams in
Geological Formations (OSPAR FRAM).
51
Seabed and overburden integrity monitoring for offshore CO2 storage
• OSPAR Recommendation 2012/5 for a risk-based approach to the Management
of Produced Water Discharges from Offshore Installations (especially relevant if
produced water is to be discharged at sea)
• OSPAR Recommendation 2003/5 related to the Use and Implementation of
Environmental Management Systems that recommends oil and gas operators to set
clear environmental objectives and targets.
The Provisions of the OSPAR FRAM are consistent with those of the EU CCS Directive and
the LP, but further guidance is provided on the information and parameters to describe the
baseline environment and the risk assessment.
A.2
European Regulations
In addition to international regulations, several European directives may impact the
member states’ legislation for CO2 subsea storage, in particular regarding environmental
baseline and near-surface site assessment.
A.2.1 Directive 2009/31/EC (CCS Directive)
This directive of the European Parliament and of the Council of 23 April 2009 on the
geological storage of carbon dioxide sets out a regulatory regime for permitting of
exploration of potential CO2 storage sites, storage operations and post closure obligations.
• Near-surface baseline data is explicitly required to describe the storage context
(Annex I.1.b, and h to k).
• Near-surface baseline data is implicitly required to conduct the risk assessment
(Annex II: hazard characterization, exposure assessment and effects assessment).
• Monitoring of fugitive emissions of CO2 at the injection site is explicitly required in the
monitoring plan (Annex II.1.1.e).
• Environmental monitoring is explicitly required to detect significant adverse effects on
the surrounding environment (Article 13.1.e), but this does not mean that it should be
included in the core monitoring program.
• Annual reporting, or more frequently if required by the competent authority, of
monitoring results and methodology (Article 14)
• The associated Guidance Document #2 (Characterisation of the Storage Complex,
CO2 Stream Composition, Monitoring and Corrective Measures) makes general
recommendations regarding baseline measurements:
• Formation gas and fluid characteristics in the storage reservoir, surrounding complex
and formations that might be affected by potential leakage, including aquifers
• Background CO2 emissions at surface or sea floor
• Surface and near surface environmental surveys
• Seabed, surface or near surface baseline surveys to define any pre-existing leakage
indicators such as pockmarks
• Ground surface surveying, e.g. where ground movement monitoring is expected to be
beneficial and/or in areas of ground movement risk.
52
Seabed and overburden integrity monitoring for offshore CO2 storage
A.2.2 Directive 85/337/EEC (EIA Directive)
This directive on the assessment of the effects of certain public and private projects on
the environment (as amended by Directive 2011/92/EU and Directive 2014/52/EU) sets out
legal requirements for member states to ensure that projects that could have a significant
impact on the environment because of their nature, size or location should receive
development consent and comprehensive prior assessment.
• Environmental baseline data is required to describe the “aspects of the environment
likely to be significantly affected by the project, including, in particular, population,
fauna, flora, soil, water, air, climatic factors, material assets, including the
architectural and archaeological heritage, landscape and the interrelationship
between the above factors” (Annex IV.3).
• Assessment of the environmental impacts is to be assessed on the basis of the
availability of environmental information and scientific knowledge.
• An environmental monitoring program may be part of the preventive measures
proposed by the operator to prevent significant adverse effects on the
environment (Annex IV.4).
• Additional monitoring may be granted if knowledge gaps were identified during the
EIA (Annex IV.8).
A.2.3 Directive 92/43/EEC (Habitats Directive)
This directive on the conservation of natural habitats and of wild fauna and flora requires
the following:
• Habitats listed in the Annex I of the Habitats Directive (“Annex I habitats”) and species
listed in the Annex II of the same Directive (“Annex II species”) require the designation
of special areas of interest, called Special Areas of Conservation (SACs).
• SACs are sites that have been adopted by the European Commission and formally
designated by the government of each country in whose territory that site lies. Sites
that are in the process of being qualified as SAC are equally considered (SCI, cSAC,
pSAC and dSAC).
• SCAs and SPAs form the Natura 2000 network of protected areas in the EU. Baseline
data is required to identify such areas (Annex I) and species (Annex II).
A.2.4 Directive 2003/87/EC (ETS Directive)
This directive on the EU emissions trading system requires the following:
• Installations are required to monitor and report their emission (planned and
unplanned). Allowances should be purchased and surrendered to cover the release
of emissions.
– ­Baseline data are not explicitly required
– Monitoring
­
activities as part of the MMV plan need to provide the input data for
emissions calculations and reporting. A combination of methods is proposed
(geophysical/acoustic method, then targeted point-based sampling)
53
Seabed and overburden integrity monitoring for offshore CO2 storage
A.2.5 Directive 2004/35 (Environmental Liability Directive)
This directive on liability for environmental damages requires the following:
• Enforces strict liability for prevention and remediation of environmental damage
to ‘biodiversity’, water and land from specified activities and remediation of
environmental damage for all other activities through fault or negligence (“polluter
pays” principle). The Directive requires setting preventive actions (Article 5) and
remedial actions (Article 6), but baseline conditions are based on
“best information available”.
• Baseline data is not required but (environmental baseline) data collected by the
operator would be used to describe the status of the environment prior to
any pollution.
A.2.6 Directive 2008/56/EC (Marine Strategy Framework Directive)
This directive establishes a framework for community action in the field of marine
environmental policy aiming at achieving and maintaining good environmental status in
the marine environment by the year 2020 (article 1.1). This framework is underpinned by
ecosystem-based approach (article 1.3) and requires Member States to define indicators,
associated targets (article 10) and monitoring programmes (article 11).
• This Directive is not directly applicable to subsea CO2 storage project but may provide
guidance regarding parameters and indicators that the regulator may want to see in
an environmental monitoring program.
These European Directives do not provide explicit requirements (i.e., are not prescriptive)
in terms of monitoring strategy and parameters. One should look at how the directive has
been transposed in the national legislation of each member state.
A.2.8 Regulatory context in the UK
The Storage of Carbon Dioxide (Licensing etc.) Regulations 2010 is the prime legislative
instrument governing CCUS in the UK. Schedule 2.2 specifically addresses monitoring and
will be fundamental to the design of store monitoring strategies.
The North Sea Transition Authority (NSTA – previously Oil & Gas Authority, or OGA)
regulates offshore carbon dioxide storage. The NSTA is the licensing authority for offshore
storage except within the territorial sea adjacent to Scotland, which Scottish ministers
authorise. Requirements of the EU EIA Directive for CGS projects are transposed into
the UK legislation in the Offshore Petroleum Production and Pipelines (Assessment of
Environmental Effects) Regulations 1999 (“the EIA Regulations”).
Data expected for the EIA are compiled in the guidance document issued by the UK
Environment Agency for the scoping of EIA of full-chain CCS project. The EIA needs to be
supported by generic and regional data, and supplemented by site-specific data, unless
it can be demonstrated that such information is not relevant for the site in question. The
need for new surveys will be discussed with the regulators and the stakeholders during the
scoping phase of the EIA.
54
Seabed and overburden integrity monitoring for offshore CO2 storage
The BEIS defines three types of monitoring: baseline surveys, site-specific surveys and
intelligent surveys. Intelligent survey means a phased approach during which information
is first collected using non-invasive geophysical techniques (such as multi-beam
echosounder and side-scan sonar) and the collected data is used to design the additional
survey requirements.
A.2.7 Regulatory context in Netherlands
Provisions of the EU CCS Directive have been transposed into Dutch legislation without
any additional technical requirement. They are addressed by The Mining Act (Ministerie
van Economische Zaken, 2011a), Decree (Ministerie van Economische Zaken, 2011b) and
Regulation (Ministerie van Economische Zaken, 2011c).
A.2.8 Regulatory context in Norway
Requirements of the EU CCS Directive have been integrally transposed into Norwegian
legislation without any additional technical requirement. Additional provisions are
resent in:
• The Royal Decree ”Forskrift om lagring og transport av CO2 på sokkelen” (Regulations
relating to exploitation of subsea reservoirs on the continental shelf for storage of
CO₂ and relating to transportation of CO₂ on the continental shelf) pursuant to the
Continental Shelf Act of 21 June 1963, managed by the Ministry of Petroleum &
Energy/Labour & Social Affairs, and
• The Pollution control regulation Part 7A., chap. 35 pursuant to the Pollution and
Waste Act of 13 March 1981, managed by the Ministry of Environment and Climate.
Table A.1, Table A.2, and Table A.3 summarize near surface data requirements in the
Netherlands, Norwegian, and UK contexts associated to the relevant
permitting milestones.
Depending on the applicable framework, monitoring data may be required at different steps
of the project to:
• Describe the context of the CGS and the “baseline scenario” based on existing data
(initial near-surface data compilation phase).
• Characterize the near-surface of a site and fill knowledge gaps (near-surface site
characterization phase).
• Provide a reference basis against which changes will be measured (near-surface preinjection monitoring phase): note that this reference basis may be time dependent
(natural or anthropogenic variability, long-term trend).
• Support the MMV plan during injection or post-injection phase (outside of the scope of
this report).
55
Seabed and overburden integrity monitoring for offshore CO2 storage
Table A.1: Subsea CO2 storage near-surface data requirements in the Netherlands
Permitting milestone
Activity & Deliverable
Environmental data
requirements
EIA – Scoping
Notice of Scope and Level
of Detail
Preliminary impact of projects
and project alternatives on:
Reference/
Guidelines
• Population
• Biodiversity, seabed,
water, air and climate,
cultural heritage
EIA – realization
Pipeline Licence
EIA reports (storage and
pipeline)
• Baseline data (see above)
Pipeline route survey
• profile of the bottom of
the sea
• Identification of
information gaps
Article 1.7.1 of
Mining Decree
• obstacles present
• location of existing
pipelines and cables
• soil mechanic
characteristics
• stratigraphy of the
bottom of the sea
• the analysis and quality of
soil samples and probes.
Storage Licence/permit
Site characterization
• Description of the
domains surrounding the
storage complex
Annex I of the EU
CCS Directive
• Population distribution
• Proximity to valuable
natural resources
• Activities around the
storage complex
• Proximity to the potential
CO2 source(s)
• Sensitivity to CO2 of
receptors
Risk assessment
• Potential leakage routes
and leakage magnitude
• Exposure assessment
based on characteristics
of the environment and
activities
• Effect assessments
based on the sensitivity
of special species or
habitats
56
Annex II of the EU
CCS Directive
Seabed and overburden integrity monitoring for offshore CO2 storage
Permitting milestone
Activity & Deliverable
Environmental data
requirements
Reference/
Guidelines
Monitoring plan
• Detecting significant
adverse effects for the
surrounding environment
Annex II of the EU
CCS Directive
• Fugitive emissions of CO2
at the injection facility
• Pre-injection baseline, as
required
Table A.2: Subsea CO2 storage near-surface data requirements in Norway
Permitting milestone
Activity & Deliverable
Environmental data
requirements
Reference/Guidelines
Proposed study
programme
Propose study
programme for Impact
Assessment to the MPE
• Preliminary
assessment of the
impact of the project
on the environment,
including cultural
monuments and
cultural environment,
any transboundary
environmental effects,
natural resources,
fisheries and society in
general
Guidelines for PDO and
PIO
• Result of consultation
of existing RIAs3 and
individual IAs should be
consulted
• Identification of
knowledge gaps
and need for
documentation and
updates
• Preliminary remedial
measures
• Identification of
applicable provisions
under the Nature
Diversity Act
57
Regulations on CO2
storage (s.4-7)
Seabed and overburden integrity monitoring for offshore CO2 storage
Permitting milestone
Activity & Deliverable
Environmental data
requirements
Reference/Guidelines
Impact Assessment (EIA)
EIA process and report
• Alternative
development solutions
Regulations on CO2
storage (s.4-8)
• Environment that may
Guidelines for PDO and
be significantly affected PIO1
• Consequences of
regular and acute
discharges on plant
and animal life
Plan for development
and operation
Proposed plans
• Description of
technical measures for
preparedness relating
to health, safety and
the environment in the
petroleum activities
Regulations on CO2
storage (s.1-10, s.4-6 ,
Appendix II)
Guidelines for PDO and
PIO1
• Proposed monitoring
plan
• Proposed plan for
corrective measures
• Proposed preliminary
plan for post-operation
Storage Permit
Characterization of the
storage
Same requirements as
CCS Directive
Appendix I of the
Regulations for CO2
storage2
Risk assessment
Same requirements as
CCS Directive
Appendix I of the
Regulations for CO2
storage2
Site characterization
Same requirements as
CCS Directive
Pollution control
regulation (Appendix I of
Chapter 35)
Risk assessment
Same requirements as
CCS Directive
Idem
Monitoring plan
Same requirements as
CCS Directive
Pollution control
regulation (s.35-9 and
Appendix II)
Environmental
monitoring
• Water column
monitoring
(Oceanographic
parameters, chemical
parameters, biological
parameters)
Guidelines for
environmental
monitoring of petroleum
activities on the
Norwegian continental
shelf
• Monitoring of benthic
habitats (grab sampling
and video surveys)
58
Seabed and overburden integrity monitoring for offshore CO2 storage
Table A.3: Subsea CO2 storage near-surface data requirements in UK
Permitting milestone
Activity & Deliverable
Environmental data
requirements
Reference/Guidelines
Storage Licence
High-level EIA
10-20 pages to
demonstrate that the
Company is aware of the
sensitivities in the area
within, and immediately
adjacent to, the block(s)
of interest, and is aware
of the potential impacts
that would have to be
managed during the
execution of the proposed
work programme
Guidance on an
application for an
offshore carbon storage
licence
Survey Licence
Licence application
Identify any areas
designated for protection
under the Habitats
Directive or Wild Birds
Directive (or that could
qualify)
The Offshore Petroleum
Production and Pipelines
(Assessment of
Environmental Effects)
Regulations 1999 (as
amended) – A Guide
Identification of Annex I
habitats
Storage Permit
Site characterization
• Identification of
environmentally
sensitive areas
• Description of the
domains surrounding
the storage complex
Environmentally sensitive
areas
Annex I to CCS Directive
• Population distribution
• Proximity to valuable
natural resources
• Activities around the
storage complex
• Proximity to the
potential CO2 source(s)
• Sensitivity to CO2 of
receptors
Risk assessment
• Review of existing well
data
• Hydraulic
communication
between geological
units
• Demonstration of
no significant risk of
leakage or of harm to
the environment or
human health
59
Guidance on Carbon
dioxide storage permit
application
Seabed and overburden integrity monitoring for offshore CO2 storage
Permitting milestone
Activity & Deliverable
Environmental data
requirements
Reference/Guidelines
Monitoring plan
Monitoring plan to
include as a minimum:
Guidance on Carbon
dioxide storage permit
application
• Seabed monitoring:
monitoring of the
seabed above the
storage site to identify
CO2 leakage (no
parameter specified).
Annex II to CCS Directive
• Fugitive emissions of
CO2 at the injection
facility.
Pre-injection baseline as
required
Pipeline Works
Authorization
Pipeline route survey
Environmental consent
Scoping of the EIA
Review of existing
environmental data:
• Population
• Biodiversity, seabed,
water, air and climate,
cultural heritage
• Seasonal variability
• Focus on
environmental aspects
likely to be significantly
impacted by the project
scoping guidance
document for CCS
projects
The Offshore Petroleum
Production and Pipelines
(Assessment of
Environmental Effects)
Regulations 1999 (as
amended) – A Guide
• Identification
information gaps and
need for new surveys
EIA report (EIS)
• Baseline surveys
• Site-specific surveys
(less than 5 years)
• Intelligent surveys
60
The Offshore Petroleum
Production and Pipelines
(Assessment of
Environmental Effects)
Regulations 1999 (as
amended) – A Guide
Seabed and overburden integrity monitoring for offshore CO2 storage
A.3. Examples of regulations from other countries
A.3.1 Australian regulations and guidelines
Currently, there is no single reference or guideline that sets out a standard for all of
Australia. It is multi-jurisdictional, with significant dependence on the Planning Approval
process. The legal framework for encouraging and regulating carbon capture and storage
(CCS) in Australia is divided among the Commonwealth and the states and territories.
The Commonwealth and some states have established CCS-specific regulations.
Commonwealth CCS legislation only applies to offshore areas that are beyond state
jurisdictions, which generally extend three miles offshore. State CCS-specific legislation
applies onshore and offshore within their respective jurisdictions. However, there is
significant variation across states and territories and though the relevant frameworks are
comprehensive in some parts of the country, they are much less so in other parts. Details
of these regulations can be found in an online article by White & Case (Power, 2021).
The Environmental Guidelines for Carbon Dioxide Capture and Geological Storage are
intended to build on the Carbon Dioxide Capture and Geological Storage – Australian
Regulatory Guiding Principles endorsed by the Ministerial Council on Mineral and
Petroleum Resources in 2005. They provide regulators, proponents, and the public with an
understanding of the application of existing environmental laws to proposed carbon dioxide
capture and geological storage projects. They are intended to demonstrate best practice
and do not seek to place additional burden on existing state and territory government
requirements. The guidelines provide steer for the environmental assessment, monitoring,
site closure, and coordination. Appropriate monitoring is considered an essential element
in the conditions for approvals for all CCS projects.
A.3.2 Japanese regulations
In Japan, several technical verification and demonstration CCS projects have been
conducted for saline aquifer due to lack of hydrocarbon fields which were ready to accept
CO2. At the time of this writing, there are no commercial scale CCS/CCUS projects nor
specific legislation to administer them.
The Mining Act and Mining Safety Act covers onshore geological storage, while the offshore
capture and storage activities are governed by Act on the Prevention of Marine Pollution
and Maritime Disaster.
According to the Act, project practitioners need to obtain an approval from Minister of the
Environment (MOE) by submitting monitoring plans prior to implementation. Monitoring
plans consists of three parts: monitoring plan for steady-state operation, monitoring plan
for needs care, and monitoring plan for emergency (Table 4).
In steady state operation phase, even if the pressure data and temperature at injection
facilities and in storage layers appear normal, if there are some exceedances found in
water sampling survey, a follow-up survey to re-confirm the pressure and temperature data
will be carried out. Based on the results of that survey, the monitoring level may need to
be increased. This three-step monitoring scheme makes it possible to elevate monitoring
levels quickly and maintain a detailed investigation over a long period.
61
Seabed and overburden integrity monitoring for offshore CO2 storage
The Act on the Prevention of Marine Pollution and Maritime Disaster imposes appropriate
requirements during injection completion and short time after completion on operator,
however there are no regulations that can consider long-term management after CCS
completion. Under the current act, project practitioner has a responsibility to renew the
approval license every five years as long as CO2 is stored. That puts operator under an
obligation to monitor CCS storage areas permanently.
In addition to the above Acts to control offshore activities, there are multiple safety laws
governing onshore facilities:
• Gas Business Act for Inlet gas line, CO2 Capture Facility (Absorption Unit), and
separated flammable gas line.
• High Pressure Gas Safety Act for CO2 lines, Capture Facility (Flash etc.) and
compressors toward the wellheads.
Monitoring plans for CCS operations has to be developed according to the relevant Acts
mentioned previously, and the operator is required to conduct monitoring and report to the
Ministry of Environment (MOE) Japan.
62
Table A.4: Overview of monitoring plan and monitoring report in Japan
Report
Same time
as chemical
property of
sea water
Continuous
Continuous
Annually
Frequency
Annually
Continuous
Pressure and
temperature
at injection
well
Same time
as chemical
property of
sea water
Continuous
Same time
as chemical
property of
sea water
Continuous
Annually
Continuous
Pressure and
temperature
at
observation
well
Condition of geological
formations and geological
features such as pressure and
temperature change
Same time
as chemical
property of
sea water
Injection activities suspended
Injection activities suspended
Annually
Continuous
Injection
pressure,
velocity and
temperature
Injection
condition
Report
Frequency
Annually
Report
Regular analysis
Alkali absorption
and Gas
chromatography
Flow meter
Continuous
Density
Disposal
volume
Frequency
Monitoring
method
Monitoring item
Steady state monitoring
Needs care
63
Emergency
1. Condition of CO2 gas
Same time
as chemical
property of
sea water
immediately
Two times
in permit
validate
period
Annually
Seismic
Same time
as chemical
property of
sea water
Continuous
Same time
as chemical
property of
sea water
Continuous
Annually
Continuous
Pressure
and
temperature
at
observation
well
Location and extent of CO2
Immediately
As needed
Immediately
As needed
Quarterly,
Immediately in
case of follow-up
survey
Quarterly,
Follow-up survey
as needed
Oceanic
environmental
survey
Chemical
property of sea
water
2. Condition of maritime area
Immediately
As needed
Quarterly
Quarterly
Oceanic
environmental
survey
Condition of
marine species
Immediately
As needed
Permit
expired year
Once in the
previous year
of permit
expiration
Desktop study
and hearing
survey
Condition
of usage of
biology and
ocean
Seabed and overburden integrity monitoring for offshore CO2 storage
Seabed and overburden integrity monitoring for offshore CO2 storage
A.4
Standards and recommended practices
Apart from regulatory requirements, there are also standards and recommended practices
relevant to seabed and overburden integrity and the examples are referenced below.
A.4.1 ISO 27924:2017 Carbon dioxide capture, transportation, and geological
storage — Geological storage
ISO 27914 focuses on the storage complex and there are only a few recommendations
regarding near-surface data. The following sections of ISO 27914 should be considered:
Section 5.5.4, Baseline geochemical characterization; Section 6.7.2.2, Process (Table 1,
Criteria number 6); and Sections 9.3.a and 9.3.b, M&V program objectives.
A.4.2 ISO/FDIS 19901-10 Marine Geophysical Investigations and ISO/FDIS
19901-08 Marine Soil Investigations
These standards are the requirements and guidelines for marine geophysical
investigations. It is applicable to operators/end users, contractors and public and
regulatory authorities concerned with marine site investigations for offshore structures
for petroleum and natural gas industries. As there are many areas of CCUS storage as yet
undefined utilizing methods from adjacent industries will be useful for defining
best practice.
A.4.3 DNV-RP-J203: Geological Storage of Carbon Dioxide
This Recommended Practice specifies:
• Near-surface baseline is required for describing the ‘context’ for site screening, site
selection, permitting, and risk management. The type of information required is in
line with the provisions of the EIA and CCS directives.
• Near-surface monitoring is required to demonstrate performance of the storage in
terms of health, safety and the environment
• Baseline monitoring prior to injection is required to define baseline against which
monitoring measurements will be compared (including temporal trends
and fluctuations)
The following section of DNV-RP-J203 should be considered: Section 5.4.4,
Environmental statement.
A.4.4 DNVGL-RP-F104: Design and operation of carbon dioxide pipelines
The following sections of DNV-RP-F104 should be considered: Section 3.2.7, Health, safety
and environment; and Section 3.4.5, Environmental impact.
64
Seabed and overburden integrity monitoring for offshore CO2 storage
Appendix B: Case studies
Marine environmental monitoring in Japan
Under the Act for the Prevention of Marine Pollution and Maritime Disaster, administered
by the Ministry of the Environment (“MOE”), operators who will work for offshore geological
storage in Japan need to establish a Monitoring Plan and then conduct monitoring during
predefined three stages (before injection – baseline surveys, during injection, and postinjection) to ensure site integrity.
The Operator for a Japanese CCS demonstration project, under the commission of the New
Energy and Industrial Technology Development Organization (“NEDO”) with funding from
the Ministry of Economy, Trade and Industry (“METI”) along with continuous monitoring of
seismicity and reservoir fluid dynamics, has carried out seasonal marine environmental
surveys including chemical measurements of seawater and sea bottom sediments at 12
selected locations.
To monitor CO2 behaviour and seismicity in and around the storage complex, downhole
pressure and temperature were continuously monitored in the injection wells and three
observation wells, and these observation wells were also equipped with downhole seismic
sensors. OBC (Ocean Bottom Cable), four OBS (Ocean Bottom Seismometers), and an
onshore seismic station have been deployed, being an integral part of spatio-temporal
monitoring of micro-seismicity and natural earthquakes, including periodical 2D and
3D surveys.
Four marine environmental surveys (seasonal baseline surveys) were conducted between
August 2013 and May 2014, to cover all four seasons. From these measurements, an initial
threshold line (upper limit of 95% prediction interval) based on the relationship between
partial pressure of CO2 (pCO2) and dissolved oxygen (DO) of sea water was drawn.
Injection of CO2 commenced in April 2016 and temporally suspended in late May for a
planned maintenance. The reservoir received 7,163 t of CO2 during this period. Original
plan was to resume injection in August, but the June marine survey reported some points
exceeded the initial threshold line, which triggered a “follow-up” survey of chemical remeasurements of sea water (round purple markers on ). Side-scan sonar survey for bubble
detection and a pH sensor survey were conducted along with the chemical measurements
at the points of exceedance. METI and MOE concluded the high values were false-positives
caused by natural variations and updated the threshold line (a solid red line on ), adding
the data from February 2017 to February 2018 surveys. They also recognized and reported
the difficulty in effectively surveying the sea-bottom soil and condition of marine organisms
as a method of detecting CO2 leakage. Therefore, operator proposed MOE to reduce the
frequency of this survey by once in a permit validity period for future projects.
There are no huge gaps between marine survey results after CO2 injection commencement
and baseline survey results. Also there are no event that may relate to CO2 leakage. From
these points, it is confirmed that CO2 is safely captured in the layers.
The project is currently in post injection monitoring period.
65
Seabed and overburden integrity monitoring for offshore CO2 storage
Experience from projects offshore Norway
One Norwegian project offers a valuable case study in offshore monitoring. The project
was initially permitted under Norwegian Petroleum Law. Subsequently, in 2015, after the
Norwegian legal framework was updated to be consistent with the 2009 EU directive on
CO2 storage, the CO2 storage operation at the site was re-permitted to be consistent with
the new directive. In the initial years, the project was used to inform the terms of the EU
directive on CO2 storage, including research on marine environmental monitoring. Various
research cruises to measure the chemistry of sediments and water column were conducted
to search for potential increased CO2 levels. No indications of leakage from the site have
been identified.15 However, concerns about possible leakage are often raised by various
stakeholders and members of the public, such that confirmation of ‘absence of leakage’
continues to be a question the operator may need to address as part of ongoing compliance
with the regulations.
15
Furre AK et al, 2017
66
Seabed and overburden integrity monitoring for offshore CO2 storage
References
IOGP Report 373-01 - Geodetic awareness guidance notes
IOGP Report 373-21 - Grid Convergence – Geomatics guidance note 21
IOGP Report 373-24 - Geomatics Guidance Note 24 – Vertical data in oil and gas applications
IOGP Report 373-16 - Guidelines for the quality control of proposed well coordinates
IOGP Report 373-18-1 - Guidelines for the conduct of offshore drilling hazard site surveys
IOGP Report 373-18-2 - Offshore Drilling Hazard Site Surveys – Technical Notes
IOGP Report 462-1 - Guidelines for the use of the Seabed Survey Data Model
IOGP Report 462-02 - Guideline for the delivery of the Seabed Survey Data Model
IOGP Report 483-7 - P7/17 Wellbore Positioning Data Exchange Format (and User Guide)
IOGP Report 483-1u - IOGP P1/11 Geophysical position data exchange format – User Guide
IOGP Report 483-6u - IOGP P6/11 Seismic Bin Grid Data Exchange Format - User Guide
IOGP Report 483-6g - Guidelines for the use of the P6 Bin Grid Data Model
IOGP Report 629 - Application of Remote Sensing Technologies for Environmental Monitoring
IOGP Report 652 - Recommended practices for measurement, monitoring, and verification plans
associated with geologic storage of carbon dioxide
Birchenough S, Williamson P, and Turley C. “Future of the Sea: Ocean Acidification.” United
Kingdom Government Office for Science. 2017.
Blackford, J., et al. “Marine baseline and monitoring strategies for carbon dioxide capture and
storage (CCS). .” International Journal of Greenhouse Gas Control 38. 2015.
Blackford J et al. “Impact and detectability of hypothetical CCS offshore seep scenarios as an aid to
storage assurance and risk assessment.” International Journal of Greenhouse Gas Control 95. 2020.
Bourne S, Crouch S, and Smith M. “A risk-based framework for measurement, monitoring and
verification of the Quest CCS Project, Alberta, Canada.” International Journal of Greenhouse Gas
Control 26. 2014. p. 109-126.
Daiji T et al. “Progress of CO2 injection and monitoring of the Tomakomai CCS Demonstration
Project.” Proceedings of the 15th Greenhouse Gas Control Technologies Conference 15-18 March
2021. Abu Dhabi. 1 April 2021.
Dean M et al. “Insights and guidance for offshore CO2 storage monitoring based on the QICS, ETI
MMV, and STEMM-CCS projects.” International Journal of Greenhouse Gas Control 100. 2020.
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Dean M and Tucker O. “A risk-based framework for Measurement, Monitoring and Verification
(MMV) of the Goldeneye storage complex for the Peterhead CCS project, UK.” International Journal
of Greenhouse Gas Control 61. 2017. p.1-15.
Furre AK et al. “20 years of monitoring CO2-injection at Sleipner”. Energy Procedia 114. 2017.
p.3916-3926.
Directive 2004/35/CE of the European Parliament and of the Council of 21 April 2004 on
environmental liability with regard to the prevention and remedying of environmental damage,
Articles 5 and 6 for EU/UK regulations
Government of Japan, Ministry of Economy, Trade and Industry (METI), New Energy and Industrial
Technology. “Development Organization (NEDO), and Japan CCS Co., Ltd. (JCCS), Report of
Tomakomai CCS Demonstration Project at 300 thousand tonnes cumulative injection (“Summary
Report”).” 2020. Available at: https://www.meti.go.jp/english/press/2020/pdf/0515_004a.pdf.
Government of Japan, Ministry of Environment (MOE). “Appropriate state of monitoring plan of
offshore CCS projects.” 2016. Available at: https://www.env.go.jp/water/kaiyo/ccs2/kanshinoarikata.
pdf.
Jones et al. “Developments since 2005 in understanding potential environmental impacts of CO2
leakage from geological storage.” International Journal of Greenhouse Gas Control 40. 2015. p.350377.
Lichtschlag et al. “Suitability analysis and revised strategies for marine environmental carbon
capture and storage (CCS) monitoring.” International Journal of Greenhouse Gas Control 40. 2021.
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Greenhouse Gas Control 65. 2017. p.218-234.
United Kingdom Department for Environment, Food, and Rural Affairs, Marine Online Assessment
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68
Seabed and overburden integrity monitoring for offshore CO2 storage
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69
The Report provides a set of
common industry good practices for
demonstrating the ongoing integrity of
an offshore CO2 storage project and to
provide assurance to the operator(s),
local regulatory bodies, or public
stakeholders that the injected CO2
remains in the storage unit over the
full project lifecycle. Using these
guidelines, the operator should be
able to demonstrate that, in the case
of anomalies or unexpected leakage
detected in the overburden and/or
at seabed, the necessary mitigation
measures are in place to identify the
issue promptly and thus reduce the
impact of the leak to a minimum level.
The scope and focus of this Report are
on the marine environment, seabed,
and shallow overburden, limited to the
units above the storage complex.
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