An XFEM implementation in Abaqus to model intersections between fractures in porous rocks

Abstract This paper presents the key aspects of the implementation of an XFEM element for hydraulic fracturing in porous medium in Abaqus. The implemented element has the capability of intersecting fractures inside an element and includes coupled hydro-mechanical behaviour and fluid exchange between fracture and the porous medium. The algorithm has three main steps: fracture geometry pre-processing, local matrix assembling, and post-processing. The first computes all the geometrical parameters of the XFEM. The second computes the jacobian and the right-hand-side matrices for each mesh element. The third checks for fracture propagation and the direction and length for propagating segments. Considering that Abaqus is a commercial software, adaptations were necessary, such as an algorithm for consideration of in-situ stress states, positioning of the degrees of freedom and numerical integration. A discussion on the limitations of the tool and of the use of the User Subroutine feature closes the implementation description. Then, we present the consolidation of a multi-fractured medium, comparing the results with a model with interface elements. In a second example, we simulate an injection in a fracture that propagates and intersects a naturally fractured model. The simulations show that the capabilities of Abaqus were considerably extended with this implementation.