Numerical Analysis of Hydrofracturing Behaviors and Mechanisms of Heterogeneous Reservoir Glutenite, Using the Continuum-Based Discrete Element Method While Considering Hydromechanical Coupling and Leak-Off Effects

Hydrofracturing technology has been widely used to stimulate the tight hydrocarbon reservoirs that usually comprise heterogeneous glutenites. Hydromechanical coupling and leak-off are essential characteristics of this process and need to be properly addressed in numerical simulation, which plays an important role in quantitatively evaluating the efficiency of this technology. Due to the challenges in accurately representing the complex structure and physical properties of heterogeneous glutenites as well as hydraulic-driven crack propagation, however, the hydromechanical coupling, leak-off, and material heterogeneity have not yet been handled satisfactorily. To overcome these challenges, we use the continuum-based discrete element method (CDEM) to simulate the hydraulic fracturing of heterogeneous glutenites, considering hydromechanical coupling and leak-off effects. The CDEM models are constructed using the geometrical and physical parameters that were extracted from natural heterogeneous glutenites using computed tomography, X-ray diffraction, and triaxial tests, based on image processing and reconstruction approaches. The CDEM models are composed of hydraulic fractures and microscale pores, and Darcy's law was integrated within the model to govern fluid leak-off; this is a nontraditional approach to leak-off effects. The coupled finite element-discrete element-finite volume approach is used to determine the fracturing behaviors of heterogeneous models. The fracturing crack propagation and distribution patterns of homogeneous and heterogeneous models under various horizontal in situ stress differences are characterized by fractal theory, and the models are compared to assess the influences of material heterogeneity and in situ stresses on the hydraulic fracturing of heterogeneous glutenites.