Influence of brine composition and fines migration on crude oil/brine/rock interactions and oil recovery

Increase in recovery of crude oil with decrease in salinity has been observed for numerous laboratory waterfloods. Repeated waterfloods on a single reservoir sandstone core indicated that potentially mobile fine particles play a key role in the sensitivity of oil recovery to salinity. This conclusion was tested using Berea sandstone after fines had been stabilized by firing at 800°C and metal oxides removed by acidizing. Recovery of crude oil from this fired and acidized sandstone was essentially independent of salinity. The presence of crude oil was also a necessary condition for sensitivity to salinity. When refined oil was used rather than crude oil, with all other conditions held the same, salinity had no effect on recovery. There was also no effect for cores that were initially 100% saturated with crude oil so that the fines were initially immersed in the oil phase. Adsorption from crude oil, the presence of potentially mobile fines, and initial water saturation are all necessary conditions for increase in oil recovery with decrease in salinity. Observed recovery behavior is ascribed to partial stripping of mixed-wet fines from pore walls during the course of waterflooding.