A Coordinate System for Local Grid Refinement Close to Wells

The construction of an orthogonal curvilinear grid is described, suitable for local refinement close to wells. The grid is obtained by conformal mapping. It is approximately polar close to the well, and provides for a smooth transition to a surrounding cartesian grid. It is shown that this grid has several advantages over competing grids. Examples illustrate that strongly improved accuracy, over coarse grid simulations, is obtainable with relatively few extra grid blocks.