Xfem modeling of stress shadowing in multiple hydraulic fractures in multi-layered formations

One of the challenges of hydraulic fracturing operations is the determination of the fluid-driven vertical fracture extent. Fracture breakout into overlaying or underlying formations with water-bearing zones can lead to irreparable water damage to the formation. In multiple fracture stimulation, stress shadowing can affect fracture geometry: length, aperture, height, and propagation direction. In this work, the Extended Finite Element Method (XFEM) was implemented in a fully coupled hydro-mechanical framework to simulate hydraulic fracturing processes considering the propagation of several vertical non-planar fluid-driven fractures. This paper focuses on the containment of multiple hydraulic fractures within the pay zone of multilayered formations. Stress shadowing effects on the required pressure for crack propagation and on the resulting fracture geometry are investigated in depth. Sequential and simultaneous fracturing schemes are considered. Our numerical results are compared to analytical solutions for fracture propagation in single and multi-layered formations under homogeneous and heterogeneous stress conditions. The predicted fracture pressure for propagation exhibits good agreement with analytical solutions for a single fracture. However, for multiple clusters this pressure must increase due to stress shadowing effects. As a result, the risk of breaking into adjacent layers is increased. Our study optimizes the injection volumes by taking into account variations of fracture spacing, reservoir thickness, fluid leak-off, formation toughness and stress contrast between layers to guarantee containment of multiple fractures into the pay zone. Moreover, strategically chosen injection times between stages maximize the operation profitability while avoiding possible aquifers contamination.