Strike-slip reactivation of a high-angle normal fault induced by increase of reservoir pore pressure: insight from 3D coupled reservoir-geomechanical modeling

Abstract

How would high-angle normal faults be reactivated under a present-day strike-slip tectonic regime if reservoir pore pressure (Pp) increased during injection operations? What parameters would control shear slip localization? To answer these questions, 3D one-way coupled reservoir geomechanical modeling of potential fault reactivation in the St. Lawrence Platform, Quebec is performed. We evaluate the risk of shear failure along the pre-existing subsurface Yamaska high-angle normal fault under the present-day strike-slip tectonic regime. Slip may be generated by pressure perturbations in deep saline aquifers of the Early Paleozoic sedimentary basin; this has implications for the assessment of risks associated with CO2 storage and deep geothermal energy potential. The Yamaska Fault is oriented NE-SW with a strike varying from subparallel to ∼35° to the orientation of maximum horizontal stress (NE63°) and dips to the SE at ∼60° with ∼800 m of vertical throw. Multiple runs of the 3D model simulate steps of increasing Pp by 4, 6, 8 and 15 MPa in the footwall sandstone reservoir at a depth of 1.25-1.5 km. Our modeling results show plastic shear deformation along the Yamaska Fault is initiated by pressure increase of 4-6 MPa. More model fault cells fail when pore pressure is increased by 8 MPa, when the reservoir pressure reaches ∼21-24 MPa, and a larger area slips during the next injection stage. The non-linear geometry of the fault results in localization of plastic shear strain on the fault segments optimally oriented, while other segments remain inactive. The dextral plastic shear deformation occurs mostly at the depth of the injection interval, propagating upward to the caprock in highly stressed fault segments. Our study helps to quantify the risk of fault reactivation induced by injection operations.