Iteratively Coupled Reservoir Simulation for Multiphase Flow

Abstract

Abstract FIM (Fully Implicit Method) and IMPES (Implicit Pressure Explicit Saturation) are two of the most commonly used time-stepping schemes in present reservoir simulation. However, neither of them satisfies the requirements of accuracy and efficiency with increasing size and degree of complexity of highly heterogeneous reservoirs. In this paper, an iterative coupling scheme is developed and applied to multiphase reservoir problems, which aims to model and simulate realistic reservoirs accurately and efficiently. Numerical examples reflecting major difficulties in treating heterogeneities and simulating complex reservoir phenomena such as coning and countercurrent flow problems are presented in comparison studies of iterative coupling, FIM and IMPES methods. Our results indicate that for the same accuracy the iterative approach can reduce computational time by 30%-40% or even more over the FIM. In comparing with the IMPES method, the iterative method shows better stability for taking larger time steps, and superior local mass balance. In this paper, the iterative approach is also shown to be scalable in parallel. Another advantage of the iterative coupled approach over FIM is that different numerical schemes and even physical models can be incorporated into the algorithm thus allowing more flexibility in treating complicated problems, e.g. highly heterogeneous reservoirs with different subdomain stochastic properties.