The numerical simulation of a 3D complex reservoir has been an important but difficult problem. One of the biggest challenges is how to deal with the large number of natural fractures with consideration of hydromechanical coupling effect in those fractures. To address this problem, a 3D hydromechanical coupled element partition method (3D-EPM) is developed. The 3D-EPM allows a fracture to run through an element without any extra degree of freedom. It can embed any number of fractures in a background mesh without mesh modification. This brings great convenience to 3D reservoir simulation. To represent the permeability of a cracked element, the equivalent permeability of this cracked element is derived based on the cubic law. To account for the hydromechanical coupling effect in a fracture, the coupled equation of 3D-EPM is developed. It is verified by the analytical model. The simulation results suggest that this method can simulate the 3D hydraulic fracture propagation, its interaction with natural fractures and the impact of in-situ stresses. This paper provides an alternative method for the 3D hydraulic fracture simulation in a complex reservoir with consideration of hydromechanical coupling effect in a fracture.

A three-dimensional (3D) element partition method for simulating fracture problems is proposed here. In this method, cracks are embedded into elements in a more straightforward manner without any nodal interpolation enrichment or any extra degrees of freedom introduced. When a crack runs across an element, the element is divided into two subbulk elements and one subsurface element. The intersection points between element edges and crack faces are taken as the virtual nodes. Thus, the displacements of the virtual nodes are the extra degrees of freedom. To eliminate these extra degrees of freedom, it is assumed that the displacements of the virtual node are related only to its adjacent nodes at the same side of the crack. The least-square interpolation technique is adopted to characterize their relationship. With this method, the cracked element deformation is related to its neighborhood. The stiffness matrix and nodal force vector are derived. The friction and contact effect between crack faces ar...