Numerical Modelling of Induced Seismicity Along a Fault During CO₂ Injection into a Subsurface Reservoir

Injection, storage, and production of fluids in geological media could be a pivotal technology in the energy transition. Injection of fluid into subsurface systems is known to have the potential to induce seismic activity. The present work models induced seismicity during CO₂ injection using a three-dimensional finite element-based numerical simulator, the Imperial College Geomechanics Toolkit. Simulations quantify fault slip along a single fault in a five-layer domain of varying permeability. Fluid injection occurs at the left boundary over a period of hundreds to thousands of days, and induced seismicity is monitored during the injection period. Results for varying mesh refinement and properties are compared against a published scenario. The originally two-dimensional model is replicated in 3D, and the same set of material properties are considered, with permeabilities ranging from 10⁻¹⁴ to 10⁻¹⁹ m². The simulations predict peak slip to within a few centimeters of that of the numerical comparison study.

The storage of gaseous fluids in porous subsurface systems such as depleted oil and gas reservoirs and aquifers is a promising method of storing renewable energy at the GigaWatt to TerraWatt scale. Geomechanical phenomena such as induced seismicity along pre-existing faults, micro-seismicity along new fractures, caprock fracturing, and surface subsidence may potentially all result from either the injection, production, or long-term storage of these fluids. Induced seismicity is important to study because geo-energy storage activities require a social license to operate from the public, and fault reactivation could displace units in a structural trap or rupture the caprock leading to seal loss and ultimately loss of the stored fluid.

To ensure a numerical simulator can accurately reproduce geomechanical behavior during the injection of gaseous fluids, its predictions should be validated against multiple analytical, semi-analytical and numerical solutions. In this paper, the results of simulations with the ICGT numerical simulator are compared with a previous numerical study (Mortezaei & Vahedifard, 2015) of fault slip during carbon dioxide injection into a subsurface geological reservoir, that was conducted with the COMSOL simulator.