Investigation of Geological Fault Reactivation and Opening

Abstract

The reactivation and opening of geological faults during reservoir injection is a relevant aspect in the design of injection pressures for hydrocarbon fields. As the pore pressure increases in the reservoir, the effective normal stresses on the fault’s plane decrease, and as a consequence, the fault slips and reactivates. Eventually, due to increasing pore pressures, the effective normal stresses decrease to zero and the fault opens. Both phenomena are undesirable since the hydrocarbon fluid can thus migrate from the reservoir to other porous layers and/or cause surface leakage. This paper investigates a simplified analytical approach for the two-dimensional analysis of fault reactivation during reservoir injection. The pore pressure increment that causes the fault to reactivate is analytically estimated for a given reservoir thickness and depth according to the Mohr-Coulomb criterion. A parametric analysis is performed and indicates the influence of geometric parameters such as the fault’s dip angle and and the reservoir’s height and depth. Finally, this simplified technique is applied to a synthetic case and final results are confronted to two-dimensional finite element simulations.