NUMERICAL SIMULATION FOR COUPLING FLOW AND GEOMECHANICS IN EMBEDDED DISCRETE FRACTURE MODEL BASED ON XFEM-MBEM

The characterization and simulation of discrete fracture networks is a hot topic at home and abroad. In the development process of unconventional oil or gas reservoir, the in-situ stress field will have a significant impact on the flow properties of fractures. If fractures are regarded as static objects, there will be a great deviation from the field data. Therefore, more in-depth research should be done based on dynamic fractures. In this paper, an efficient hybrid numerical discretization method is proposed to solve the coupled mechanical problems of coupling geomechanics and fluids flow in tight oil reservoirs. The extended finite element method (XFEM) is used to solve the elastic deformation of rock, and the mixed boundary element method (MBEM) is adopted to accurately calculate the unsteady flux between matrix and fracture. The two numerical schemes are fully-coupled and the time-terms in overall calculation scheme is solved by the fully-implicit method, which can accurately and efficiently simulate the mechanism of fracture deformation and fluids flow in the development of tight oil reservoirs. In addition, the embedded pre-treatment is used to characterize the large-scale hydraulic fracture, and the effect of proppant is considered. The dynamic information of matrix and small-scale natural fracture can be captured by using the double-porosity effective stress principle and the characterization method of implicit fracture in dual-media. Therefore, the hybrid model proposed in this paper comprehensively characterizes the complex system composed of matrix, natural fractures and hydraulic fractures. The accuracy of proposed model is demonstrated by several examples in this paper. The study shows that the influence of the flow parameters change and the fracture aperture reduction caused by stress-field can not be ignored when evaluating the productivity of fractured horizontal well in tight oil reservoirs. This work can provide theoretical guidance for the development of unconventional oil and gas resources.