Abstract
In black oil simulation, the areal block size can have a magnitude of 100 m by water drive and can extend to 1000 m by depletion drive. EOR displacement processes such as miscible and steam drive, surfactant flooding and in situ combustion require 10 to 0.5 m grid spacing. This is technically impossible in field scale simulation which uses a conventional Cartesian grid.
This paper, based on the control volume discretization technique, shows that local grid refinement is a straightforward extension of industry standard methods. Applying some simple rules, the locally refined grid is strictly orthogonal, even at the fine-coarse grid transition. This orthogonality is a fundamental requirement to make sure that the numerical solution converges to the true one if the grid size is reduced.
Since small block size is only required at the displacing front, local grid refinement is applied only in this area and moves forward in time. With dynamic grid refinement, the down-streams block ahead of the front are subdivided before the displacing front arrives and they are gathered again when the front has passed them. By gathering the blocks outside the EOR area, the overall block number can be reduced considerably without neglecting the influences of the environment.
An example for missible hydrocarbon gas drive illustrates the combination of dynamic grid refinement and gathering, showing that a field scale EOR displacement can be simulated with small block size without exceeding the technical and economic limits.