Image courtesy of Sanjay Srinivasan, UT-Austin
High resolution inverted seismic images of CO2 migration at the Cranfield, Mississippi field injection site: a) Areal view of the reservoir after injection at a depth of 3000 m below the surface showing CO2 migration (indicated by purple shaded areas within and outside the circled region) near the injection wells. (b) Areal view of the rock layer above the injected zone, at a depth of 2600 m below the surface, showing no evidence for leakage of CO2 through the reservoir seal.
Computation algorithms were developed to increase the information content from time-lapse seismic data at CO2 geologic storage sites. This unique seismic inversion technique images the thin layers of rock that can influence the migration of the CO2 plume, providing a high-resolution monitoring capability. The effectiveness of the technique was validated with the time-lapse surface seismic surveys at the Cranfield Mississippi field CO2 sequestration demonstration site.
Removal of CO2 from the emissions of fossil fuel plants is a priority for clean energy. One method involves sequestering the CO2 underground after collection from the power plants. The high-resolution imaging capability will offer more effective monitoring of CO2 plume migration during geologic sequestration, enhancing the prospects for this potentially impactful technology.
A powerful new “seismic inversion” technique uses time-lapse seismic data to make high resolution images useful for evaluating subsurface migration of CO2 following geologic sequestration. Migration of CO2 alters the mechanical properties of porous rocks which can be monitored from high frequency rock property variations embedded in the seismic amplitude data. The technique utilizes a dictionary of seismic “wavelets”, information derived from seismic data before CO2 injection, and an optimization algorithm to identify the set of common wavelets that best describe the variations in seismic amplitudes observed pre- and post- CO2 injection. The University of Texas-Austin team applied it to investigate the migration pathways of the CO2 plume at the Cranfield, Mississippi field demonstration site where such time-lapse surface seismic surveys are available. The raw seismic data showed only a weak signature of CO2 injection. However, “seismic inversion” of the data enhanced the information content, showing that the injected CO2 migrated mostly along the top of the layer of rock into which it was injected, but there was no leakage through the reservoir seals. This technique affords an effective way to monitor potential leakage of CO2 plumes at various reservoirs.
Director of the Center for Frontiers of Subsurface Energy Security (CFSES) EFRC
University of Texas at Austin
Basic Research: DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program. Cranfield site seismic data was obtained from research supported by the Office of Fossil Energy at the National Energy Technology Laboratory.
Zhang, R., Ghosh, R., Sen, M.K. and Srinivasan, S., “Time-lapse surface seismic inversion with thin bed resolution for monitoring CO2 sequestration: A case study from Cranfield, Mississippi,” International Journal of Greenhouse Gas Control, [DOI: 10.1016/j.ijggc.2012.08.015], September 2012.
Center for Frontiers of Subsurface Energy Security
DOE Fossil Energy Carbon Sequestration Regional Partnerships Program
Southeast Regional Carbon Sequestration Partnership