Investigation of Smart Water Flooding in Sandstone Reservoirs: Experimental and Simulation Study Part2

Abstract

In this paper, we considered the effect of water chemistry on water-rock interactions during seawater and smart water flooding of reservoir sandstone cores containing heavy oil. Oil recovery, surface reactivity tests, and multicomponent reactive transport simulation using CrunchFlow were conducted to better understand smart water flooding. Secondary water flooding with FW at 25°C resulted in an ultimate oil recovery (UOR) of ~50% OOIP for all reservoir cores in this study. Formation water salinity was 104,550 ppm. FW was diluted twice to obtain SMW1. SMW2 was similar to SMW1 but depleted in divalent cations (Ca2+ and Mg2+). SMW3 was also similar to SMW1 but depleted in Mg2+ and SO42-, while SMW4 was the same as SMW1 but Ca2+ was diluted 100 times. Seawater salinity was 48300 ppm, which is close to the smart waters salinity (52275 ppm). No oil recovery was observed during SMW1 flooding, while softening SMW1 (SMW2) resulted in a significant additional oil recovery OOIP. Depleting Mg2+ and SO42- resulted in additional oil recovery but smaller than in SMW2. Diluting Ca2+ 100 times was the second best scenario coming after depleted Ca2+ in SMW2. The results of this study showed that the more diluted Ca2+ is in the injected brine, the more additional oil recovery that can be obtained, even though the other divalent/monovalent cations/anions were increased or decreased or even depleted. Other reservoir cores were allocated for surface reactivity test. The absence of an oil phase allows us to isolate the important water-rock reactions. The Ca2+, Mg2+, and SO42- effluents for all cores were matched using CrunchFlow, and then further investigations of the water-rock interactions were conducted. The reactive transport model showed that decreasing the Mg2+ concentration will decrease the number of the most effective kaolinite edges Si-O- and Al-O-, but was not as pronounced as that in present of Ca2+, which explains why lowering Mg2+ concentration gives lower additional oil recovery, and why lowering Ca2+ concentration gives higher additional oil recovery.