New insight to experimental study of ionic solutions with a non-ionic surfactant on wettability, interfacial tension and micro-model flooding

Wettability alteration (Delta theta), changes in interfacial tension (Delta(IFT)) and fluid pH are investigated for Asmari formation carbonate and sandstone reservoirs of the large Ahwaz oil field (Iran) with a range of low salinity waterbased fluids accompanied by a non-ionic surfactant (LSWF-surfactant) and the acidic (total acidic number = 0.58 mg KOH g(-1)) Asmari crude oil. On initial contact with the LSWF-surfactant the carefully prepared reservoir rock slices, soaked and aged in the crude oil all displayed oil-wet states. Metal-salt (potassium chloride, sodium sulfate, magnesium sulfate heptahydrate, calcium chloride dihydrate and lithium chloride) enriched aqueous solutions of various concentration (1000-4000 ppm) mixed with 400 ppm Triton (TM) X-100 (surfactant) were used in the Delta theta, Delta IFT and pH tests. The test results for these variables suggest that the calcium chloride dihydrate (4000 ppm) solution with surfactant has the most beneficial impacts on both the carbonate and sandstone reservoir samples evaluated in terms of improving oil mobilization. Glass micro-model fluid-flow experiments to evaluate and compare oil recovered by secondary recovery (LSWF only injected) and by tertiary recovery (LSWF-surfactant injection) confirm the rock slice tests, with calcium chloride dihydrate achieving substantially higher ultimate oil recovery than the other LSWF solutions tested.

Automated summary

The study investigated the impacts of low salinity waterbased fluids and a non-ionic surfactant on wettability alteration, interfacial tension changes, and fluid pH in Asmari formation carbonate and sandstone reservoirs. Experimental results showed that the calcium chloride dihydrate solution with surfactant had the most beneficial effects on improving oil mobilization in both reservoir samples. Glass micro-model fluid-flow experiments confirmed the efficacy of calcium chloride dihydrate in achieving higher ultimate oil recovery compared to other solutions tested.