Effects of Rock Components on Enhanced Oil Recovery by Low-Salinity Waterflooding in a Limestone Formation: A Case Study of an Iranian Oil Field

HOSSEINIAN, ARMIN; NazariSarem, Mahdi

doi:10.22050/ijogst.2026.368129.1661

Effects of Rock Components on Enhanced Oil Recovery by Low-Salinity Waterflooding in a Limestone Formation: A Case Study of an Iranian Oil Field

Document Type : Research Paper

Authors

ARMIN HOSSEINIAN ¹

Mahdi NazariSarem ²

¹ Postdoctoral Fellowship, Department of Earth Science and Ocean, University of British Columbia, Vancouver, Canada Post Doctorate Fellowship, Department of Earth Science and Ocean, University of British Columbia, Vancouver, Canada

² Department of Petroleum, Mining, and Materials Engineering, CT.C., Islamic Azad University, Tehran, Iran

https://doi.org/10.22050/ijogst.2026.368129.1661

Abstract

The mechanisms underlying low-salinity water (LSW) flooding in carbonate reservoirs remain less well understood than those in sandstone reservoirs. This study investigates the role of rock composition through a comparative experimental analysis of natural limestone from the Shadegan oil field and pure synthetic calcite. Core-flooding experiments, contact angle measurements, zeta potential analysis, and pH monitoring were conducted under reservoir conditions of 70 °C and 100 bar. The results showed that tertiary LSW injection recovered 14.5% of the initial oil in place from the limestone, compared with only 3.4% from pure calcite. This substantial difference was attributed to a more pronounced wettability shift toward water-wet conditions in the limestone, as evidenced by a 42° reduction in contact angle compared with a 16° reduction in calcite. This wettability alteration was associated with a stronger negative shift in zeta potential in the natural limestone (−7.7 mV) than in the pure calcite (−4.1 mV). X-ray fluorescence (XRF) analysis revealed the presence of silica, sulfate, and phosphate impurities in the limestone, which enhanced the alteration of surface charge. These findings indicate that trace non-clay minerals can significantly enhance the effectiveness of LSW flooding in carbonate reservoirs, providing new insights into the optimization of enhanced oil recovery (EOR) in complex carbonate formations.

Highlights

· The mechanisms governing low-salinity water (LSW) injection in carbonate reservoirs are complex.

· Key parameters, including contact angle, zeta potential, and pH, should be investigated to better understand the underlying mechanisms.

· LSW injection demonstrated enhanced potential for improved oil recovery (EOR) in both natural and synthetic limestone rocks.

· The crude oil–brine and rock–brine interfaces exhibited different wettability responses during tertiary LSW injection.

Keywords

Enhanced oil recovery

Low salinity water

Wettability variation

Surface electric charge

Zeta potential

Subjects

Petroleum Engineering

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