Analysis of the Hydrogeological Conditions Affecting Fault Response to Nearby Hydraulic Fracturing

Abstract

The response of critically stressed dormant faults to fluid perturbation, by oil and gas production, has been a major public concern because of its link to induced seismicity. In this paper, we study the hydrogeological factors that affect a nearby fault response, during and after hydraulic fracturing (HF) operations, evaluated by the change in Coulomb Failure Stress (CFS) through coupling solid deformation and fluid flow. We take the Duvernay formation in Alberta, Canada as a base study case for our analysis. Our results show that the injection rate and the fault's distance to HF operations play an important role in increasing the CFS and hence the probability of fault reactivation. When the fault is far from the operations, its damage zones allow lateral diffusion and prevent pore pressure build up in its upper part, which stabilizes it. The lower part, however, will be under a lower normal stress and its failure may be triggered by an increase in shear stress. This is not the case for close faults where the damage zones act as conduits for pressure diffusion and the possible triggering failure mechanism will be the increase in pore pressure. Moreover, we show that the width of the HF zone does not affect the activation mechanisms or the stability of the fault unless it is hydraulically connected to its damage zone. Therefore, serious attention should be given to the fault position, its architecture, and the volume of fluid injected to help reduce the potential for induced seismicity from HF.