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Article Type

Review Article

Corresponding Author

Bayram Gasimov

Highlights

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Abstract

Capillary hysteresis is a pore-scale phenomena that has considerable influence on oil displacement, residual oil trapping, phase connectivity, and efficiency of oil recovery in porous media. Although enhanced oil recovery (EOR) techniques are often evaluated based on their effectiveness in interfacial tension reduction, wettability change, mobility manipulation, and capillary number change, capillary pressure hysteresis, relative permeability hysteresis, and displacement histories have often been overlooked. This review examines capillary hysteresis-induced mechanisms and discusses how drainage-imbibition path dependency, contact angle hysteresis, pore-scale trapping, mobilization of ganglia, scanning curves, and rate effects affect oil recovery efficiency. The discussion in this review is based on a critical examination of experiments, theories, pore-scale imaging, and numerical simulations in the literature about capillary pressure hysteresis, relative permeability hysteresis, wettability change, and cyclic displacement processes. Capillary hysteresis affects not only the degree of oil entrapment but also that of remobilization of the entrapped oil through changing the relationships between saturation, capillary pressure, and mobility. Mechanisms, including snap-off, ink-bottle effect, contact-line pinning, and throat constriction, trap oil in isolated ganglia, while wettability change, interfacial tension reduction, controlled injection sequence, and pressure gradient can restore connectivity of the trapped oil. Techniques like surfactant flooding, low-salinity waterflooding, nanofluids, cyclic injection, and water-alternating-gas injection are considered to be major methods by which hysteresis effects can be modified. The main conclusion from the review is that capillary hysteresis should be treated as an active displacement-control mechanism rather than a passive secondary effect in EOR design

Keywords

capillary hysteresis; Enhanced Oil Recovery; residual oil saturation; drainage–imbibition cycles; wettability alteration; relative permeability hysteresis.

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