Locally Streamline-Pressure-Potential-Based PEBI Grids

Abstract Streamline pressure-potential (SPP) grids are a very promising tool for reservoir simulation, allowing to honor the actual path of flow. These grids represent a successful combination of streamline simulation and finite difference methods. One of the major challenges of this technique is that with changing flow conditions the grid needs to be altered over the period of a simulation run. This paper presents the application of the windowing technique, introduced by Deimbacher and Heinemann1, to locally honor the changing directions of flow by modifying the grid during a simulation run. One or multiple parts of a reservoir model can be represented by windows with the objective to minimize the grid orientation effect and to enhance the CPU performance by locally incorporating time dependent streamline pressure-potential based PEBI grids. In a first step the fully implicit solution for the full model will be calculated, but the inner blocks of the window, represented by a fine scale Cartesian grid, are solved for pressure only. Saturations and mole fractions will not be updated during this step. The solution of the first step provides the boundary influx for the windows and the pressure distribution that allows to determine the grid points of a streamline – pressure potential grid. Based on this point distribution a new window grid will be constructed using the PEBI algorithm. The new grid will then be solved in a second step, where the window is calculated for the same overall timestep, using the boundary flux determined during the first step. The paper describes the generation of locally streamline based PEBI grids and presents results obtained from the application of this technique. A small scale example highlights the advantages of the proposed technique to handle the grid orientation effect. A further example demonstrate the application of the technique in full scale simulation models.