Many reservoirs in North America contain a high water saturation zone "bottom-water" underlying the oil zone. Waterflooding under such conditions is typically ineffective because of chanelling of water through the bottom-water zone. However, in some cases, waterflooding such reservoirs may still be feasible and economically viable. While there is no doubt that some of the injected water bypasses the oil zone through the bottom-water zone, most of the injected water may still displace the oil, depending on the reservoir conditions. Therefore, a mechanistic understanding of oil displacement by a waterflood in the presence of a bottom-water zone is the basis for predicting recovery performance, and there is a need for developing a mathematical model to describe water channeling under bottom-water conditions.
In this paper, a new simple analytical model was developed to predict waterflood performance in stratified reservoirs when a water zone is present. Given the reservoir description, the new mathematical model can be used to describe the amount of water channeling into the bottom-water, calculate pressure distribution in each layer and together with a prediction of oil recovery. Results of the mathematical predictions are compared with experimental and simulation results, showing good agreement.