A discrete modeling framework for reservoirs with complex fractured media: Theory, validation and case studies

Abstract

An unstructured discrete fracture model (UDFM) is developed in this study to simulate the two-dimensional fluid flow in the complex fractured tight oil reservoirs. The model applies a control-volume finite-difference (CVFD) discretization scheme with the two-point flux-approximation (TPFA) to evaluate the transmissibility list. Discretization process of the mathematical model is greatly simplified by three differential operators that are defined to represent the expressions of divergence, gradient and average as their original forms, and thus, enable rapid prototyping of the numerical model. The discretized equation system is solved by a modified Newton's method, in which the Jacobian matrix is computed by the automatic differentiation (AD) technique. Our model is validated with the simulation results obtained by the commercial reservoir simulator, Eclipse. To test the model's potential in field-scale application, we implement it in five large-scale complex fractured systems that are radial domains with a uniform diameter of 1000 m but different fracture densities: 382/km2, 509/km2, 636/km2, 764/km2 and 1018/km2. Simulation results not only indicate the robustness of our model in simulating complex fractured systems but also highlight the significant effects of fracture network configuration and fracture density on the development features of fractured tight oil reservoirs.