CO2 sequestration: Seismic characterization of potential CO2 leakage through compacting shales
This Master's project was assigned to Emilie Sofie Rong who started her Master's program in Earth Sciences, UiB, in the fall semester 2023. The Master's project is given by the research group Geophysics.
Conservation of CO2 sequestrated in subsurface reservoirs is of major importance for this technology to succeed in reducing emission of CO2 into the atmosphere. The principle of CO2 sequestration is to inject CO2 into a subsurface reservoir rock and prevent it from migrating upwards to reach the surface. Shales act as both source rocks to hydrocarbons, but do also most often form the seal layer or cap rock preventing oil and gas from migrating out of the underlying reservoir. Shale integrity relates to its resistance to conduct vertical fluid flow and links to its vertical permeability. Shale integrity increases during mechanical compaction (burial) as the flat clay particles become more aligned, again decreasing the ability of vertical fluid flow. If shales start cracking, which can happen if the pore fluid pressure exceeds the confining pressure or due to tectonic processes, they lose integrity and pore fluids in reservoirs below may start to leak vertically through the shale layer. The thesis will address how seismic data can indicate shale integrity.
Hypothesis (scientific problem):
The effect of mechanical compaction on shale integrity may be estimated from modelling of internal alignments of clay minerals. In addition to mechanical compaction, the volume of silt and quartz within the shales have severe impact on how the overall alignment as these grains prevent local alignment. Alignment properties can be described by using geometrical distribution functions, which subsequently can be used to estimate how seismic properties in shales alter with compaction. Compaction of shales implies seismic anisotropy, which is important to consider in seismic inversion and seismic reservoir characterization. The problem is to review the various mechanisms influencing shale integrity during compaction by modelling shale texture for various types of shales, and, furthermore, apply this to estimate seismic anisotropy. Finally, these results can be reviewed in terms of typical seismic attributes such as acoustic and elastic impedances or amplitude versus offset signatures.
The work shall review models for compaction of shales under various conditions and translate these models into parameters which are relevant for estimating seismic properties. Then these parameters shall be used to model seismic attributes (as described above) by combining anisotropic rock physics and seismic models. Finally, the combined effects of shale integrity and CO2 leakage on seismic data shall be outlined.
Bachelor in geophysics