Modelling Residual Oil Saturation in Miscible and Immiscible Gas Floods By Use of Alpha-Factors

Abstract

Abstract For miscible gas flooding, it has been documented that forcing a residual oil saturation Sorm is helpful to make the compositional simulations more realistic. Our recent experience is that this concept can be extended to near-miscible and even immiscible gas floods. For CO2 floods, we have found that preventing this residual oil saturation from being stripped by the gas corrects overestimation of the recovery factor in compositional simulation, even at pressures lower than the miscibility pressure. This residual oil saturation can be implemented with the use of Alpha-Factors (named also transport coefficients). Their physical meaning will be discussed, and also a way to generate them. Our method is to use an iterative process based on a PVT package, and analytical equations allowing to compute their endpoints are given. Also some limitations of the approach will be discussed, such as grid size dependence, a weak pressure dependence and a strong dependence on the injected gas composition.