Containment of Water-Injection-Induced Fractures: The Role of Heat Conduction and Thermal Stresses

Abstract

Summary Reservoir cooling by water or wastewater injection can significantly change the stress in the target injection zones and the bounding layers. Out-of-zone fracture growth is substantially affected by these poro-thermo-elastic stress changes occurring in heterogeneous rock layers. No previous study has systematically investigated the influence of both heat conduction and convection and the associated stress alteration and fracture height growth during long-term water injection in multiple layers. Without understanding this coupled effect, it is not possible to predict the injection-induced fracture geometry or the conditions under which these fractures will breach the bounding shale layers. This paper presents a model and results that clearly show that accounting for thermal conduction between the injection sand and the bounding shale is crucial in predicting fracture containment during water injection. We developed a fully coupled compositional reservoir/fracturing simulator that solves poro-thermo-elastic equations. We used it to simulate 3D fracture propagation induced by cold water injection and, at the same time, calculate changes in the stress field induced by thermo-poro-elastic effects in heterogeneous reservoir layers. The stress in the bounding layer is shown to change significantly as a result of thermal conduction from the layer below. We first validate our model with existing analytical solutions and then present synthetic cases and simulate a field case. Simulation results show that fracture height growth can be underpredicted if heat conduction between the target injection sands and bounding shales is ignored. We identify the effects of fluid properties, rock properties, and injection temperature on thermal-conduction-induced stress changes and fracture containment for the first time.