RESERVOIR SIMULATION GRIDS - OPPORTUNITIES AND PROBLEMS

Grid selection is one of the most difficult and time-consuming tasks i n the simulation of geologically complex reservoirs. A grid is imposed on a reservoir so that we can solve the nonlinear flow equations that predict the reservoir's response to changes at wells or other boundar ies. Therefore, I first discuss the role of grid geometry in the evalu ation of each term in the flow equations. Then I describe several conv entional and some new gridding techniques, as well as their advantages and disadvantages. Next I make recommendations based on my own experi ence and discussions with colleagues. My assessment is that grids shou ld be as close to orthogonal as possible. Also, local grid refinement should be used with care; its inappropriate use can be counterproducti ve. Considerable progress has been made recently on the use of flexibl e grids, but efficient use of unstructured, locally orthogonal grids r equires further research. Techniques that automatically align the grid with major reservoir features (e.g., faults) are being developed and are expected to simplify grid generation.