Effect of Mineralogy on Initial Wettability and Oil Recovery from Silica-containing Chalk

Summary Carbonate rock wettability is influenced by polar components in the crude oil, rock mineralogy and brine composition. Previous studies on chalk suggest that exposure of a large amount of acidic crude oil to core material reduces water wetness, thus affecting the ultimate oil recovery achieved during waterflooding. Presence of silica in the pore space appears to affect the wetting state of chalk toward more water-wet conditions. This study evaluates the wetting effect of crude oil exposure on the silica-rich Aalborg chalk, and its impact on oil recovery. Spontaneous imbibition and forced imbibition tests have been conducted at 50 °C to evaluate initial wetting and its effect on oil recovery from three silica-rich (6.8 At%) outcrop Aalborg chalk cores. Various amounts of crude oil was injected during core preparation, and it was observed that as the amount of crude oil injected increased, less water-wet conditions were obtained. A higher degree of water wetness in the Aalborg chalk core promoted higher ultimate oil recovery under forced imbibition than that previously reported for Stevns Klint chalk, containing low silica content. It was concluded that the silica content in the core induced a more water-wet wetting state in the core.