Concurrent production and injection in stacked reservoirs as commonly conducted in unconventional resource exploitation potentially influences reactivation of nearby faults. Using three-dimensional, fully-coupled poroelastic finite-element simulations, we assessed the potential for reactivation of a barrier normal fault in a normal-faulting stress regime for twelve generic injection–production scenarios that differ in the depth of injection and production, and in the position and distance relative to the dipping fault plane. The simulations display significant variation in the Coulomb failure stress (CFS) with depth along the fault plane for these scenarios, reflecting differences in pore pressure distribution and associated poroelastic changes in normal and shear stress across the fault. Based on the CFS trends with depth we find that 1.) concurrent production and injection reduces or increases the fault reactivation potential in the injection reservoir depending on the lateral position and the distance of the wellbores relative to the fault plane; 2.) the fault is most prone to reactivation with stacked wellbores and injection into the upper reservoir within the hanging wall or the lower reservoir within the footwall, and 3.) the fault is least prone to injection-induced reactivation for stacked wellbores and injection into the lower reservoir within the hanging wall at wellbore-to-fault distances ten times the reservoir thickness. With decreasing wellbore-to-fault distance, induced poroelastic shear stresses and thus CFS increase, making injection only into the lower reservoir, without concurrent production, the most stable configuration at close distance. These simulations demonstrate the importance of the coupled poroelastic effects and of the three-dimensional arrangement of injection and production wellbores on fault reactivation. Our results are intended to provide general guidance for further detailed site-specific geomechanical evaluations needed for induced seismic hazard assessment.

在非常规资源开采中通常会同时进行的叠层油藏生产和注入可能会影响附近断层的复活。使用三维全耦合多孔弹性有限元模拟，我们评估了在十二种普通注入-生产方案（其注入和生产深度不同）下，在正断层应力状态下重新激活势垒正断层的潜力。相对于倾斜断层平面的位置和距离。在这些情况下，模拟显示库仑破坏应力（CFS）随断层深度的变化很大，反映了孔隙压力分布的差异以及断层上法向应力和剪切应力的相关孔隙弹性变化。根据CFS深入的趋势，我们发现1。）同时进行生产和注入，取决于侧向位置和井眼相对于断层平面的距离，减少或增加注入储层中的断层再活化潜能；2.）断层最容易被叠置的井眼激活，并注入到悬壁内的上部储层或底盘内的下部储层，并且3.）断层最不容易被注入诱导的叠层井眼和注入的复活到井壁到断层的距离是储层厚度的十倍，进入悬挂壁内的下部储层。随着井眼到断层距离的减小，引起的孔隙弹性剪切应力增加，从而导致CFS增大，使得仅向下部油藏注水，而没有同时生产，近距离处的井眼构造最为稳定。这些模拟证明了孔隙弹性耦合效应以及注入井和生产井眼的三维布置对断层活化的重要性。我们的结果旨在为诱导地震危险性评估所需的进一步详细的特定于场地的地质力学评估提供一般指导。