Prediction of Waterflood Performance in Stratified Reservoirs

Abstract

ABSTRACT Crossflow between adjacent layers plays an important role on water flooding performance in a stratified reservoir; however, the analytical solutions describing the crossflow effect are possible only under limiting conditions: (i) where viscous forces are dominant (no crossflow); and (ii) where vertical equilibrium exists (gravity and capillary dominated displacement). This study analyzes the effect of crossflow on the waterflooding performance by comparing simulator results under actual flooding conditions with the approximate analytical solutions. The parameters varied include the injection rate, vertical permeability variation, ordering of beds, mobility ratio and the ratio of vertical to horizontal permeabilities. A five beds, linear model was used under wide range of operating conditions. Based on the study, it was observed that the oil recovery and cross flow index were dependent on the value of RL (effective length to height ratio) for favorable mobility ratios, and on the value of RD (vertical to horizontal pressure gradients ratio) for unfavorable mobility ratios. Ranges of RL and RD were established for which approximate analytical solutions are valid. For the intermediate region (where both viscous and gravity forces are important), empirical correlations for crossflow index were developed.