A novel analytical solution to assess induced seismicity in pressurized and depleted reservoirs

International audienceThe use of the subsurface has increased significantly in the last years to contribute to a low-carbon economy. This intensive use has led to an increased number of induced seismicity cases. In particular, the presence of displaced faults crossing the reservoir could significantly increase induced seismicity. To minimize its risk, understanding and predicting the stress variation along faults is a requirement. To this end, we have developed a novel analytical solution based on the inclusion theory. The solution predicts the stress response to pore pressure variations within the reservoir. We consider both permeable and impermeable faults and a fault offset that ranges from zero to the reservoir thickness. The analysis of fault stability changes caused by reservoir pressurization/depletion under different scenarios reveals that (1) the induced seismicity potential of impermeable faults is always larger than that of permeable faults; (2) reversed slip in normal faults with a normal faulting stress regime is observed at the corners of the reservoir due to stress concentration; (3) fault offset has no effect on stability changes in impermeable faults, but permeable faults show an increasing slip potential with the offset, showing that non-displaced permeable faults are the safest scenario; (4) neglecting the poromechanical coupling results in overestimation of the induced seismicity potential and underestimation of the injectivity. This analytical solution provides fast estimates of fault stability changes and thus, it is a useful tool for site selection and for assisting pressure management of geo-energy projects