Connection element method for reservoir numerical simulation

Abstract

<p indent=0mm>Abstract: The reservoir numerical simulation presently encounters problems based on the fine grid. These include poor convergence and difficult history matching. In practical application, the coarse grid often leads to the destruction of the flow structure and the significant reduction of the prediction accuracy. This paper proposes a new reservoir numerical simulation method different from the traditional grid-based methods. The proposed method discretizes the reservoir calculation domain into a series of connection elements from the flow perspective. According to the physical properties of nodes, the support domain and the moving least squares are used to estimate the Laplace operator of pressure and provide the calculation method of the attribute parameters reflecting the flow ability (connection transmissibility) and mass basis (connection volume) of the connection element. Taking the connection element as the object, the flow flux in the element is obtained by solving the node pressure equation. The transport equation about saturation is also solved by using a semianalytical method along the connection element to obtain the production dynamics. The path tracking algorithm is introduced to quantitatively represent the flow interaction and connectivity between the source and sink nodes. Finally, a reservoir numerical simulation method based on the connection element system, which is referred to herein as the connection element method (CEM), is introduced. Practical applications show that the CEM can realize the fast prediction and history matching of the reservoir production performance and identification of the injection-production connectivity. The conceptual example also verifies that in the case of the same node (grid) distribution, the CEM shows better calculation accuracy and efficiency compared with the traditional finite difference method. At the same time, the node allocation in the CEM is more flexible and can ensure the flow path integrity under fewer nodes to improve the prediction accuracy. It also supports the parallel computing of transport equations on connection elements. In conclusion, the CEM can better meet the requirements of the rapid prediction of actual large-scale reservoirs and provide a new idea for reservoir numerical simulation with complex geometric characteristics, such as fracture, fracture-cavity type, and complex boundary.