NUMERICAL SIMULATION OF MULTI-SCALE FRACTURED RESERVOIR BASED ON CONNECTION ELEMENT METHOD

In order to solve the complex geometric characteristics description and dynamic connectivity identification problems of reservoir at different scales, a new method of reservoir numerical simulation, connection element method (CEM), based on non-European physical connectivity network with meshless characteristics has been developed in recent years. In this paper, CEM is extended to fractured reservoirs. From the perspective of fluid flow, the reservoir is discretized into physical connected network by the connection element. The generalized difference approximation of the pressure diffusion term is given according to the physical parameters of the node, the radius of the influence domain and the weighted least square method. Meanwhile, the control volume of nodes, the transmissibility between matrix nodes, the transmissibility between fracture nodes, and the transmissibility between matrix nodes and fracture nodes were calculated based on the material conservation equation. Thus, a fully implicit discrete scheme of seepage control equations is constructed to solve dynamic production parameters such as pressure, saturation and water cut. Based on the pressure gradient between nodes solved by each time step, the allocation factors of injection wells at each time step were calculated by the depth-first search algorithm of graph theory to quantitatively characterize the flow relationship and connectivity between well nodes. The algorithm validation shows that the method can freely and flexibly portray complex reservoir geometry including distribution of complex fractures networks and irregular reservoir boundaries. Compared with the traditional grid-based method, this method can retain more abundant flow topologies under the condition of coarser model, so as to achieve a better balance between computational accuracy and computational efficiency. As a result, CEM can better meet the demand of production dynamic simulation and prediction of actual large-scale fractured reservoirs, and provides a new idea for numerical simulation of fractured reservoirs with multi-scale geometric characteristics and complex boundary reservoirs.