Laboratory demonstration of the impact of weak interfaces and layered rock properties on hydraulic fracture containment and height growth

Abstract

Hydraulic fracturing and waterflooding are both widely applied methods for improving the recovery of oil and gas resources. These methods have increasing commonality because many waterfloods are being carried out at high enough pressure to generate hydraulic fractures. Even so, it is challenging for engineers to make an optimal wellbore pressure design for layered and otherwise complex underground formations. An overly aggressive injection pressure may lead to uncontrollable fracture height growth into non-producing layers adjacent to the reservoir. In contrast, when using classical but highly simplified height growth models, the pressure limits can be far too conservative which may lead to lower recovery rates and inefficient use of resources invested in developing producing reservoirs. Therefore, it is necessary to investigate the mechanism of fracture height growth while considering the coupling effect from multiple dominated factors. This research contributes an experimental approach to evaluating the role of stresses, weak interfaces, and mechanical properties of a three-layer system in promoting or containing hydraulic fracture height growth from a central reservoir into neighboring barrier layers. In all cases, the experiments agree that the pressure required to induce substantial height growth exceeds the stress applied to the barrier layers and is far above classical predictions. Additionally, when the reservoir layer is softer than the barriers, the containment is sustained to even higher pressures than for layers with similar material properties. Finally, the experiments show that permeability of the barrier layer can induce a more sudden transition to uncontrolled height growth when fracture reaches the bedding interfaces. Hydraulic fracture height growth is mitigated by weak interfaces between layers. Unstable height growth typically requires fluid pressure to exceed the in-situ stress in the bounding layer(s). Contrasting layer stiffness and permeability often leads to further mitigation of height growth.