Tensor Character of Pore Pressure–stress Coupling in Reservoir Depletion and Injection

Abstract

The state of stress within and around a reservoir is a key parameter for fluid flow, fracture stimulation, design of wellbore arrays and wellbore stability. Therefore pore pressure induced stress changes (pore pressure/stress coupling) have immediate implications for the reservoir management. We analyze the effects of pore pressure changes on the individual components of the principal stress tensor and not only the minimum horizontal stress component. The results show that pore pressure stress coupling has a tensor character and can cause significant changes in the stress field within the reservoir as a function of distance to the injection point and tectonic regime. The tensor character of pore pressure/stress coupling leads to changes in the differential stress of the system which is essential for fault reactivation. It is demonstrated that injection as well as depletion can lead to fault reactivation, and that the rock stability depends on the tectonic regime and on the location with respect to the injection (depletion) point. Furthermore, the tectonic regime can be locally modified within the reservoir. Thus an improved understanding of pore pressure/stress coupling effects contributes to fault seal prediction, optimized placement of in-fill wells, stimulation operations and wellbore stability assessment.