Abstract
Wettability alteration (Δθ), changes in interfacial tension (ΔIFT) 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 water-based 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™ X-100 (surfactant) were used in the Δθ, ΔIFT 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.
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