The New EOR Frontiers - Reduced Salinity Waterflooding

Abstract

Reduced salinity waterflooding is a new EOR technique in which the salinity of injection water is tuned to improve oil recovery compared to conventional seawater flooding or other higher saline water.  Simply injecting enough reduced salinity waterflooding water in sandstone reservoirs has been reported to increase oil recovery under certain conditions. Three main possible mechanisms regarding Reduced salinity waterflooding have been proposed in literature despite the lack of universal justification of how the process works improving oil recovery. A common feature among the suggested mechanisms is the release of divalent cations from the rock surface.  Several schools of thought have hypothesised that Reduced salinity waterflooding results in change in wettability of the sandstone rock. As a consequence the previously attached oil mostly to clay minerals (kaolinite) is then released and floated away. Numerical simulation concept was used to model reduced salinity waterflooding water injection on field scale at reservoir conditions. The model was used to examine the effect of slug injection of reduced salinity waterflooding water, barriers preventing vertical flow, connate water banking, grid refinement and variation in the position of high permeability layer on field oil recovery factor and cumulative oil produced. The study indicated that Reduced salinity waterflooding is recovers more oil when the high permeability layer is positioned on top and when the low salt water is injected in the oil leg. The slug injection concept reduces the requirements for reduced salinity waterflooding water flood and recovers nearly the same percentage of oil. The study concluded that reduced salinity waterflooding water injection yields higher recovery and has more economical potential compared to other conventional water flooding systems. Sensitivity analysis on timing illustrated that early start of reduced salinity waterflooding water injection is immensely beneficial to Reduced salinity waterflooding improved oil recovery technique.