DALKHAA, C. & OKANDAN, E.
Department of Petroleum and Natural Gas Engineering
Middle East Technical University (METU), Turkey
INTRODUCTION
STATIC EXPERIMENTAL RESULTS
For the prevention of injected CO2 leakage into atmosphere, the possible paths and the
mechanisms triggering the paths must be examined and identified.
It is known that the leakage paths can be due to CO2 - rock interaction and CO 2 – well
interaction after massive injection of CO2.
This study focuses on the CO2 - rock interaction . Although supercritical CO2 is normally
inert, when it dissolves in brine, it makes formation water acidic. This acidized formation
water reacts with the surrounding rock minerals and thus geochemical reactions, dissolution
of primary minerals and precipitation of secondary minerals, take place. These reactions
can change the porosity and affect the permeability and furthermore the sealing capacity of
cap rocks.
I. FLUID CHEMISTRY ANALYSIS
Table1. Water compositions prior to and after the experiment
Dissolved elements in
the formation water
After the
Change
Prior to
experiment
thru the
experiment
(30 days) experiment
(ppm)
OBJECTIVE
Sodium
693,2
752,7
59,500
Calcium
41,92
382,2
340,280
Magnesium
47,36
152,1
104,740
Iron
1,190
0,443
-0,747
15
117,18
102,180
Chloride
725
903,26
178,260
Bicarbonate
613
628
15,000
Sulfate
The aim is to investigate geochemical reactions between the injected CO2, the cap rock
formation water and the cap rock minerals by laboratory analysis and mathematical
techniques and their impact on the sealing capacity of cap rock.
At the end of this thesis work, mineral analysis of Sayindere formation, the cap rock of
Caylarbasi field in Turkey will be made and the mineral reactions with the injected CO2 and
synthetically prepared formation water will be identified. Moreover, a geochemical modeling
of the CO2 sequestration will be developed and the porosity and permeability change of the
formation will be identified and thus how the sealing capacity of the cap rock will be affected
will be discussed as a result of the rock-injected CO2-formation water interaction.
MATERIALS AND METHODS
Collection of necessary materials for the experimental work
-cores from Sayindere cap rock formation
-formation water analysis results of Caylarbasi Field
Preparation of synthetic formation water
Fluid chemistry analysis (prior to and after the experiment) to measure the available dissolved
elements in the formation water by following techniques:
- IC
- ICP-EOS
- titration
- pH
Mineral investigation (prior to and after the experiment) to identify the rock compositions by
- Thin section analysis
- SEM (Scanning Electron Microscopy)
- XRD (X-Ray Diffraction)
Carry out the static and dynamic experiments
Geochemical modeling and simulation using TOUGHREACT
II. SEM ANALYSIS OF THE CORE
From the following photos taken in SEM analysis, it is seen that near to
surface there is a lighter coloured layer, which was caused by the contact with
carbonated water.
This side
was in
contact
with CO2
saturated
water
This side
was in
contact
with CO2
saturated
water
Fig 3. Side view of the core top surface after 30 days Fig 4. Side view of the core top surface after 100 days
III. CONCLUSION
It may explain:
The Ca bearing minerals are dissolved into the CO2 saturated
formation water because, from the water analysis given in Table 1, the
Ca ion concentrations increased from 41.92 ppm to 382.2 ppm through
the first 30 days
(The elemental analysis of the SEM also supports the explanation given
above.)
THIN SECTION ANALYSIS OF THE CORE
FUTURE WORKS
FROM SAYINDERE FORMATION
A matrix of very fine grained calcite and clay minerals.
The porosity and permeability are very low.
Many lighter and darker laminations with thickness of 0.1-0.8 mm.
Tiny cracks parallel to these laminations are filled or stained with iron oxide.
A lot of fossils.
A few rounded quartz, a small number of hematites and glauconites are found
STATIC EXPERIMENTAL WORK
In static experiment, the original core is put in the core holder and filled with CO2 saturated
synthetic formation water and is left for 30 days under a pressure of around 100 bar (1450 psia)
and a temperature of 90°
°C, representing the field conditions.
I. DYNAMIC EXERIMENTAL WORK
Core will be grinded into 100 mesh size -150 micron
XRD analysis of the powdered core will be made and then packed
into the core holder.
CO2 and water mizture will be injected to the packed core at the
previosly determined rate.
Injected and produced water analyses will be made at diffrent time.
II. REACTIVE TRANSPORT MODELING & SIMULATION
After the experiments, a geochemical modeling of the CO2
injection into the Sayindere formation will be constructed and
simulation works will be done by using TOUGHREACT.
ACKNOWLEDGMENT
The Scientific and Technological Council of Turkey (TUBITAK) is
greatly acknowledged to fund my doctorate study. Petroleum Research
Center (PAL) and Department of Petroleum and Natural Gas
Engineering, METU are also acknowledged to provide the financial and
technical support to carry out this work.
Fig 1. Static experimental scheme
Fig 2. Photo of static experimental set-up