The Effect of Crossflow on Waterflooding of Stratified Reservoirs

Abstract

Abstract A mathematical model is developed for waterflooding performance in linear stratified systems for both cases of non-communicating layers with no crossflow and communicating layers with complete crossflow. The model accounts for variation of porosity and saturation in addition to permeability of the different layers. The model predicts the fractional oil recovery, the water cut, the total volume injected, and the change in the total pressure drop, or the change in injection rate at the water breakthrough in the successive layers. A systematic procedure for ordering of layers and performing calculations is outlined. A procedure for combining layers to avoid instability in the case of low mobility ratio is introduced. The developed model is applied to different examples of stratified reservoirs. The effects of mobility ratio and crossflow between layers are discussed. The effects of variable porosity and fluid saturation are discussed also. It was found that crossflow between layers enhances the oil recovery for systems with favorable mobility ratios (λw/λo < 1) and retards oil recovery for systems with unfavorable mobility ratios. It was found also that crossflow causes the effect of the mobility ratio on oil recovery to become more pronounced. The variation of porosity and fluid saturation with permeability is found to increase oil recovery over that for the case of uniform porosity and saturation for both favorable and unfavorable mobility ratios.