A New Grid Block System for Reducing Grid Orientation Effect

The grid orientation effect (GOE) is a long-standing problem plagueing reservoir simulators that employ finite difference schemes. A rotation of the computational grids yields a substantially different solution under certain circumstances. A Cartesian grid with one axis parallel to the line joining an injector and producer gives a solution significantly different from a grid that has the axes oriented at 45° to this line. This article presents a new grid system that can reduce the grid orientation effect. This system involves using a unique grid-block assignment where rectangular grid blocks are interspersed with octagonal grid blocks. The boundaries are populated with triangular grid blocks. The entire domain consists of a “structured” grid block system referred to as the hybrid grid block (HGB).