Semi-analytical models for stress change and fault reactivation induced by reservoir production and injection

Abstract

A change in fluid pressure within a porous reservoir will generally induce stress changes within the reservoir and the rocks that surround it. Amongst the potential hazards resulting from these induced stress changes is the reactivation of existing faults or fractures, which may breach the hydraulic integrity of the caprocks that bound the reservoir. Fluid production and injection-induced stress changes in poroelastic media can be modeled using the theory of inclusions. Semi-analytical solutions of this type are presented in this paper for horizontal and dipping reservoirs of finite depth with rectangular and elliptical cross-sections, under plane strain conditions. Stress change parameters calculated using these equations are charted for different reservoir geometries and depths using dimensionless parameters, to facilitate their application to a broad range of reservoir depths and dimensions. Equations are also presented to assess the fault reactivation tendency resulting from induced stress changes using the Coulomb Failure Stress Change method. Fault reactivation analyses conducted for a horizontal reservoir of rectangular cross-section show that, during depletion, there is a tendency towards fault reactivation in the rocks near the lateral flanks of the reservoir, and within the central portion of the reservoir, in a normal fault stress regime. For a similar case in a thrust fault stress regime, there is a tendency towards fault reactivation in the rocks above and below the reservoir, but there is no tendency towards fault reactivation anywhere within the reservoir during depletion. It is also shown that fault reactivation potential is dependent on reservoir geometry and dip angle.