Grid-Orientation Effects and the Use of Orthogonal Curvilinear Coordinates in Reservoir Simulation

Grid orientation effects in reservoir simulation recently have received considerable attention. Several authors have proposed methods to reduce or to eliminate these effects. However, the proposed methods require reprograming of simulators based on standard techniques. The reprograming effort can be considerable if the numerical model is highly complex, such as in steamflood simulation. An orthogonol curvilinear coordinate system was investigated which essentially eliminates the problem of grid orientation. With no reprograming, this computing grid can be used readily in existing simulators. Such grids have been used to study pattern steamfloods and pattern waterfloods. The results are compared in detail with those obtained by using conventional Cartesian grids. Grid orientation is shown to have a more pronounced effect on the saturation fronts than oil recovery, whether in a steamflood or a waterflood. It is concluded that orthogonol curvilinear grids can be easily used to estimate pattern flood performance without program modification. (12 refs.)