Investigation of the Sweep Efficiency for a Vertical Cross-Sectional Displacement in Irregular Heterogeneous Reservoirs

To obtain a better insight into the displacement efficiency in heterogeneous reservoirs, a cross-sectional study for a pair of vertical injection and producing wells is considered. Geostatistical modeling is employed to simulate various cases of realistic reservoir heterogeneity between the wells. This is coupled with reservoir simulations of immiscible displacement to evaluate the sweep efficiency. Two groups of similarity criteria characterizing the heterogeneous lithology distribution and the fluid flow are proposed. One group is used to distinguish and delineate the limiting cases of homogeneous and layered reservoirs. The other group is used to distinguish and constrain the limiting cases of gravity-driven flow and displacement in anisotropic reservoirs. The main conclusions of this study are obtained using a parametric investigation into the displacement efficiency in various reservoirs. Furthermore, the uncertainty propagating from reservoir heterogeneity to the efficiency is addressed. It is shown that the displacement is generally more efficient in the reservoirs built of thin and extended interlayers. It is also more efficient at larger net-to-gross ratios; however, in a specific limiting case of a large buoyancy force, an optimal net-to-gross ratio exists. The physical mechanisms resulting in such optimal values and their potential applications in well placement are discussed.