What geomechanical parameters constrain induced seismicity during CO₂ sequestration: lessons learned from observed microseismicity at Decatur

Induced microseismicity has been detected in the Decatur CO₂ sequestration area, providing valuable insight into the stress state of the reservoir. To assess the full stress tensor, we performed an inversion using source mechanisms of the induced microseismic events. The inversion also incorporates additional data, including the vertical stress gradient and ISIP pressures measured in the area. The resulting stress tensor is then used to estimate the minimum activation pressure required to trigger seismicity on fault planes identified by the source mechanisms. Comparing the minimum activation pressure with injection pressure suggests that either ISIP pressures are significantly lower (~28-29 MPa), or the maximum horizontal principal stress is very high (>120 MPa), or the coefficient of friction on the activated faults is below 0.6. Key measurements for future CO₂ sequestration sites should include ISIP pressure and/or maximum horizontal pressure.