A Dynamic Discrete Fracture Model for Fluid Flow in Fractured Low-Permeability Reservoirs

Abstract

Abstract Waterflooding has been an effective method for improving oil recovery process of Low-Permeability Reservoirs. Tight Low-Permeability reservoirs are characterized by natural fractures, hydraulic fractures, and induced fractures by water injection. These fractures may have a significant impact on process performance and ultimate recovery. The interaction between pre-existing natural fractures and the propagating fractures are critical factors affecting the complex fracture network. It is a great challenge to model accurately fluid flow due to the multi-scale nature of the problems and the strong coupling that exists between flow and mechanical behaviors. In this paper, a dynamic discrete Fracture modeling approach was developed and implemented which enabled integrated simulation of fracture network propagation, interactions between hydraulic fractures and pre-existing natural fractures, fracture fluid leak off and fluid flow in reservoir. We apply the Discrete Fracture Modeling (DFM) approach to represent large-scale fractures individually and explicitly. The model allows inclusion of the impact of stress regime on fluid flow in a discrete fracture network. This entails highly constrained unstructured gridding and construction of a connection (transmissibility) list of all neighboring cells. A methodology for modeling fracture propagation in length- and height-direction is presented with respect to poro- and thermo-elastic stresses acting on the fracture. The method was solved using the discrete fracture control volume method. Results were obtained in terms of saturation and pressure distribution for various fractured porous media. Comparisons for simulation results and well production performance show an excellent match. The new model allows us to better understand the multi-scale and multi-physics flow behavior caused by complex fracture system. Sensitivity studies by varying the production rate, pressure and fracture parameters could be conducted to provide guidance on optimizing production designs. The simulation results show that reservoir dynamic fractures play an important role in both direction and speed of water displacement fronts through tight low-permeability reservoirs. The oil recovery rate significantly depends on the fractures orientation and the rate of fracture growth. The proposed simulation method provides a useful tool for modeling the effect of fractures on waterflooding performance and can be used to optimize injection pressures and rates, water quality as well as well patterns for maximizing oil recovery.