Geomechanical Assessment of Seismic Hazard Associated with Drilling a Well through a Fault

This study described a coupled hydro-mechanical geomechanical model to examine pore pressure and stress changes resulting from drilling a well through a fault, to see the induced fault slip scenarios and its corresponding moment magnitudes and deformation to assess seismic hazard, which is assumed to be relatively low. Thus the analysis focused on a worst case scenario whereby the entire fault slip was assumed to occur as a single seismic event. Analytic and geomechanical models indicated that the elastic stress changes around the borehole would only result in a relatively small magnitude −2 event. For the planned mud weight density no additional slip was estimated, nonetheless for a higher mud weight, the model indicated localized fault slip as the pressure diffused into the fault that could increase the magnitude up to −0.1. In all scenarios, only relatively small magnitudes were estimated and not large enough to be felt on surface. Seismic monitoring with a local array while the well was drilled did not detect any events, consistent with the predicted seismic magnitudes.