Harold Pearson-Nadal, Everett Criswell
GeoSci 440
Demian Saffer
Drilling Proposal #2
The proposal we read was titled “Gas Hydrates on the Cascadia Margin” submitted to the
IODP website by Michael Ridel. The proposal is for ocean drilling in order to generate more
accurate models on marine gas hydrate formations in zones of subduction and accretion. To do
this, Ridel et al. proposes, in addition to drilling, measurements of boreholes as well as continued
recording of these sites which occur across the Northern Cascadia accretionary prism. The
project intends to continue on the research done during Leg 146 of Cascadia hydrate drilling
project as well as Leg 204 off the coast of Oregon which solely concentrated on the structure of
the hydrate ridge there, an issue the new project seeks to avoid because of its limited
applications.
This proposal was chosen because of its relation to climate-change and sedimentology.
The project is related to sedimentology because gas hydrates, the focus of the proposal, are
typically stored in relatively shallow sediment layers at the bottom of the ocean, therefore some
knowledge of sediment layering is necessary to pursue gas hydrate deposition. On the other
hand, the proposal has a climatology related basis as well because of the connection between gas
hydrates and global warming. Gas hydrates are theorized to contain the majority of methane, the
sudden release of which could significantly increase greenhouse gas levels and therefore increase
global temperatures.
Objectives
The proposal has many objectives, most of which seem to revolve around some lightly
studied aspect of gas hydrates and methane. Ridel lists the origin of this deep-water methane, its
transport up through the ocean, the role of methane in gas hydrates, as well as the loss of
methane to the seafloor as the main objectives of the project. In addition, the project seeks to
address the diverse layer of hydrate that occurs above the stability field which Ridel et al. states
“make up the largest volume of hydrate globally”.
Moreover, methane fluxes that occur in channels and lead to the formations of
concentrated seafloor hydrates are important to the project because they are essential in
establishing the connection between climate change and marine hydrates. The proposal also
includes a short explanation of the model it seeks to address, mentioning the process is driven by
merging at accretionary prisms. The proposal lists more general objectives of the project as well,
including the testing of proposed gas hydrate models and factors that limit the parameters of the
model.
Data
In order to test the gas hydrate model and the factors that limit it, Ridel plans to collect
data on vertical concentration distributions of free gas and hydrate deposits and their position in
the accretionary prisms. The project would also require estimates of methane fluxes in the
sediment which, as the proposal states, can be calculated as a function of distance between land
and zone of deformation. In addition, the proposal mentions that long-term borehole monitoring
will secure data on impacts of sediment compaction processes and periodic fluid transport in
establishing hydrate deposits.
Locations and Justifications
The diverse population of accretionary prisms is likely the reasoning behind this location.
As previously mentioned, the authors designate accretionary prisms as the primary force behind
the methane sequestration process and this location would provide various opportunities to
collect data to possibly support this theory
One way the data in this study will be collected will be via long term monitoring in the
boreholes. This will assist in determining the role of shaking in the sediment consolidation,
episodic upward fluid transport, and hydrate formation. We will also be able to track the history
of methane in an accretionary prism form. This historical record of methane will be generated
from its production by mainly microbiological processes over a thick sediment vertical extent, its
upward transport through regional or locally focused fluid flow, and its incorporation in the
regional hydrate layer above the BSR or in local concentrations at or near the surface. Other
ways we can track the history of methane include measuring methane loss from the hydrate by
upward diffusion and by recording the methane oxidation and incorporation in seafloor
carbonate, or expulsion to the ocean. There are a number of necessary facilities for this proposal:
the now well-developed CORK downhole monitoring, Log-While-Drilling (LWD), Distributed
Temperature Sensors (DTS), and a Pressure Core Barrel sampler for hydrate, free gas, and fluid
recovery under in situ conditions. This proposal fits the goals for gas hydrate drilling of the ODP
Gas Hydrates Program Planning Group. The first of these goals is to study the formation of
natural gas hydrate in marine sediments. The second goal is to determine the mechanism of
development, nature, magnitude, and global distribution of gas hydrate reservoirs. The third goal
is investigating the gas transport mechanism, and migration pathways through sedimentary
structures, from the site of origin to the reservoir. The fourth goal is to examine the effect of gas
hydrate on the physical properties of the enclosing sediments, particularly as it relates to the
potential relationship between gas hydrates and slope stability. The fifth and final goal is to
investigate the microbiology and geochemistry associated with hydrate formation and
dissociation. These scientific goals are an expansion of the latest achievements of ODP Leg 204,
dedicated to study gas hydrates at Southern Hydrate Ridge (Trehu et al., 2002).