ABSTRACT

Rock mechanics plays an important role in the performance assessment of geologic carbon dioxide (CO2) sequestration, including assessment of caprock sealing performance, ground-surface deformations, potential fault reactivation, and induced seismicity. As a practical example, recent results are reviewed from studies of the geomechanical aspects and modeling associated with CO2 injection at the In Salah CO2 storage project, around the Krechba gas field, Algeria. The site is an ideal test bed for geomechanical studies: the CO2injection pressure is sufficiently high to cause measurable groundsurface deformations, and the targeted injection zone consists of fractured sandstone intersected by minor faults. At Krechba, satellite-based interferometry (InSAR) is used to monitor ground-surface deformations with remarkable precision (a few millimeters), because of favorable ground-surface conditions, including hard desert sediments and bare rock. Inverse semianalytical strain analysis as well as coupled fluid flow and geomechanical numerical modeling are being employed to interpret observed ground-surface deformations in terms of underground fluid movements and structures, such as faults and fracture zones. Significant modeling effort is currently being dedicated to analyze ground-surface uplift at one of the injection wells, where a double-lobe uplift pattern indicates opening of a deep fault or fracture zone—a feature that has also been detected in a recent 3D seismic survey. Finally, coupled fluid flow and geomechanical modeling has been applied to estimate the potential for injection-induced microseismicity. For the best-estimated present-day strike-slip stress regime at Krechba, the current analysis indicates a relatively low potential for injection-induced microseismicity. The geomechanical models are being updated and recalibrated as new field data becomes available, and the long-term geomechanical responses will be assessed.

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