Recent Updates on Smart Water EOR in Limestone

Abstract

Experimental data confirm that the EOR-effects observed during Smart Water flooding can be explained by wettability alteration toward more water-wet conditions. Detailed knowledge about the important crude oil – brine – rock parameters affecting reservoir wetting, fluid flow and wettability alteration in oil reservoirs is needed when Smart Water EOR potential for reservoirs should be predicted. Both field observations and laboratory experiments confirm that seawater behaves as a Smart Water in limestone reservoirs, significantly improving the oil recovery. Laboratory core experiments have been performed to evaluate the effects of polar components present in crude oil on core wettability during core restoration. Spontaneous imbibition and viscous flooding oil recovery tests have been performed on the restored cores to evaluate the effect of initial core wettability on ultimate oil recoveries. The results have been compared with oil recovery tests that include wettability alteration induced by Smart Water. The experimental results confirmed that adsorption of polar components in crude oil dictates the core wettability established during the core restoration, and strongly water-wet outcrop cores became mixed-wet. The amount of oil that the core was exposed to affected the degree of water wetness, and therefore the crude oil amount needs to be accounted for in core restoration procedures. Oil recovery experiments showed that the ultimate oil recovery increased with increasing water wetness in the cores, confirming that increased positive capillary forces, resulting from wettability alteration, significantly affected fluid flow in porous media, improving oil recovery. The results are in line with the proposed chemical Smart water EOR model valid for both carbonate and sandstone. Wettability alteration toward more water-wet conditions induces increased capillary forces and improved microscopic sweep efficiency. Ultimate oil recovery in was significantly influenced by the core wettability, increasing with water wetness, confirming that capillary forces is an important recovery parameter. Only small changes in core wetting have significant effects on ultimate recoveries, confirming that laboratory core restoration procedures need to be optimized when recovery potentials for reservoirs should be estimated.