Effect of acid number of crude oil on oil recovery of smart water coupled with silica nanoparticles

Spontaneous imbibition (SI) is one of the most important mechanisms in reservoir engineering. In order to activate of this mechanism completely in carbonate reservoirs, wettability of these oil wet rocks should be altered to water-wet. Multi-step spontaneous imbibition tests were designed and conducted in this study. Results indicated that mixture of smart water and nano silica could increase oil recovery up to 5 percent. Effect of acid number of crude oil on oil recovery of this mixture was investigated by using three samples of crude oil during SI tests: A (0.38 mg KOH/g), B (0.25 mg KOH/g) and C (0.18 mg KOH/g). Maximum oil recovery of SI tests was recorded for oil sample C which had lowest acid number. Ion analysis of imbibing fluids indicated sharp reductions in concentration of sulfate ion in each step of SI tests which confirmed occurrence of ion exchange mechanism in the rock surface of core samples.