Low salinity water injection: Impact of physical diffusion, an aquifer and geological heterogeneity on slug size

This paper uses numerical simulation to investigate the impact of physical diffusion/dispersion on oil recovery from low salinity water injection. It focuses particularly on how slug size is affected by the interaction of longitudinal and transverse mixing with reservoir heterogeneity and an aquifer. Previous work, which focussed only on the impacts of longitudinal dispersion in a homogeneous reservoir, suggested that a slug size of ∼0.4 PV would recover almost as much oil as continuous low salinity water injection. This study suggests that a slug size of at least 0.6 PV is needed in heterogeneous reservoirs, in the absence of an aquifer. The presence of an aquifer in combination with diffusion means that even very large slugs are degraded to the point where there is little benefit from low salinity injection. These conclusions apply whether low salinity water is injected immediately production begins or following conventional, high salinity waterflooding. In layered systems, transverse diffusion can result in significant improvements to incremental oil recovery over that which would be achieved in the absence of diffusion.