Any analysis of hydro-mechanically coupled production processes needs to consider flow in fractures and matrix coupled simultaneously. In this paper, fractures were described explicitly using a discrete fracture model. The fluid exchange term in the matrix and fracture governing equations was used to couple the flow in the fracture and matrix. Based on poroelasticity, the momentum and mass coupling of the standard equation were established for fractured porous media. An improved extended finite element method (I-XFEM) was used, and a solver was developed to solve the fully coupled model efficiently. In this model, fractures are decoupled from the grids, and the calculation efficiency was improved greatly. The improved enrichment functions were used to characterize the physical field and guarantee the calculation accuracy. The accuracy of the model was verified using a single-fracture model. A multi-fracture model was designed. The results showed that the cumulative production is positively related to the Elastic modulus and Poisson's ratio, indicating that solid deformation on reservoir development has a significant influence and that the Elastic modulus and Poisson's ratio have a significant effect on the reservoir stress sensitivity.
Many natural fractures often develop in fractured reservoirs, and there are obvious heterogeneity and multi-scale characteristics. Fractures are the main channel of fluid flow, which has a significant impact on the fluid pressure field and solid stress field. In addition, for low-permeability and ultra-low permeability reservoirs, hydraulic fracturing has been widely used. While improving the fluid flow conditions and production rate, it greatly strengthens the spatial multi-scale characteristics, anisotropy, and heterogeneity of reservoirs, making it very difficult to simulate the underground fluid flow and predict production in a dynamic production process in such reservoirs.
Terzaghi [1,2] was the first to examine the hydro-mechanically coupled problem and gave an empirical formula of effective stress for the first time. Biot [3,4,5] proposed the modified effective stress formula based on Terzaghi. Rice (1976) and Coussy (1995) then successively developed the related theory [6,7]. Hydro-mechanically coupled problems have always been a major focus [8,9,10,11]. In recent years, there has been increasing research on hydraulic fracturing [12,13,14]. In this paper, based on poroelasticity, the underground fluid pressure field was coupled with the stress field of solid rock. The fluid in the fracture was treated as a viscous fluid, and the simplified Navier-Stokes equations were used to describe the fluid flow in fractures. The flow equation in the fracture cross-section could be averaged because the fracture cross-section size was smaller than its length. The fluid flow of matrix and fracture was coupled with the fluid exchange terms on the fracture surface. On this basis, a fully coupled production model was established.
