Experimental investigation of low salinity enhanced oil recovery potential and wettability characterization of Alaska North Slope cores

Abstract

Rock wettability and the chemical properties of the injection water influence fluid distribution and multiphase fluid flow behavior in petroleum reservoirs and hence it consequently affects the final residual oil saturation. Many researchers have proven that oil recovery is increased by decreasing the salinity of water used for waterflooding process. Three sets of experiments were conducted on representative Alaska North Slope (ANS) core samples to experimentally ascertain the influence of injected brine/fluid composition on wettability and hence on oil recovery in secondary oil recovery mode. All the sets of experiments examined the effect of brine salinity variation on wettability and residual oil saturation of representative core samples. The core samples used in the first and third set were new (clean) while in the second set core samples were oil aged. For first and second sets laboratory reconstituted 22,000 TDS, 11,000 TDS and 5,500 IDS (total dissolved solids) brines were used while for the third set ANS lake water was used. Oil aging of core decreased the water wetting state of cores slightly. This observation could be attributed to adsorption of polar compounds of crude oil. The general trend observed in all the coreflood experiment was reduction in Sor (up to 20%) and slight increase in the Amott-Harvey Wettability Index with decrease in salinity of the injected brine at reservoir temperature.