Effect of Injection Strategy on Induced Seismicity Risk during CO2 Storage

Numerous studies in CO2 sequestration sites have shown that CO2 injection can cause significant geomechanical changes, depending on the injection pressure and site-specific geomechanical conditions. Even if significant seismicity is not observed, the fluid injection can induce local stress changes, which can permeate further away and can lead to geomechanical complications far from the injection area. Understanding the stress perturbation due to fluid injection aids in comprehending the fault activation mechanism and the risks of induced seismicity. The current study evaluates the geomechanical influence of CO2 injection in a depleted oil field and compares the pore pressure buidlup and the risk of injection-induced seismicity due to different well placement strategies. The Cambay basin in western India is chosen for the study. We carried out fluid flow modeling combined with geomechanical analysis to study and contrast the hydro-mechanical characteristics of CO2 injection through a single-well and 2-well injection strategy, keeping the amount of CO2 injected equal. A quantitative risk analysis of induced seismicity was then conducted for both cases through simulation of fault slip potential in the field. Probabilistic FSP analysis indicates that a 2-well injection leads to a significantly lower risk of fault slippage than a single-well injection due to delocalization of pore pressure buildup. The results suggest that a multi-well strategy can be quite useful in highly fractured reservoirs where faults are closer to being critically-stressed.