A Computational XFEM Hydraulic Fracture Model for Analyzing Caprock Breach in Layered Formations

ABSTRACT: A critical challenge in CO2 storage operations is controlling and predicting vertical fracture growth resulting from CO2 injection. Geological formations consist of layers where each has varying mechanical properties and in-situ stress fields, creating contrast between the layers. When an unwanted hydraulic fracture encounters weak or strong caprocks, the propagation characteristics are affected due to the non-local character of a hydraulic fracture influencing the pressure and associated fracture geometry. In this work, we employ an XFEM in a fully coupled hydro-mechanical framework to analyze a vertical fluid-driven fracture breaching the caprock. The fracture is driven in a multi-layer and permeable formations by injecting an incompressible viscous fluid at the fracture inlet assuming that the fracture propagates under plane strain conditions. Fluid flow in the fracture is modeled by lubrication theory and the pore fluid movement in the porous formations is based on the Darcy law. The coupling follows the Biot theory while fracture propagation criterion is based on cohesive damage mechanics. The investigation is performed numerically with Abaqus to obtain the fracture opening, length, and propagation pressure versus time and length. The unwanted hydraulic fracture was successfully validated against the k-dominated regime with zero leak-off. Results showed that caprock breach produces wider profiles in soft evaporites and narrower in hard shales. Also, the pressure profiles increase in both cases when the fracture penetrates the caprock.