Summary

Tight rock reservoirs have gained popularity and become a subject of great interest because of their huge recovery potential. A substantial portion of the potential hydrocarbon could be removed from the reservoir by injecting solvent gases [hydrocarbon or carbon dioxide (CO2)] as an enhanced-oil-recovery (EOR) application. Achieving precise modeling of these processes and an accurate description of hydrocarbon dynamics requires a clear understanding of phase-change behavior in a confined (capillary) medium. It was previously shown that early vaporization of liquids could occur in channels that were larger than 1000 nm. The surface wettability plays a critical role in influencing the vaporization and condensation nature in confined systems. This paper studies the influence of the medium wettability on phase-transition temperatures of liquid hydrocarbons in macrochannels (greater than 1000 nm) and nanochannels (less than 500 nm) by using different types of rock samples. The boiling temperature of hydrocarbon solvents was measured in two extreme wetting conditions: (1) strongly water-wet and (2) strongly oil-wet. Boiling temperatures of heptane and octane in sandstone, limestone, and tight sandstone were observed to be lower than their bulk boiling points by 13% (4% in Kelvin units), on average. Altering rock wettability characteristically changes the average hydrocarbon nucleation temperatures, being as critical as the pore size. Changing sandstone’s wettability to strongly oil-wet shifted the average nucleation temperature of heptane and octane by 6% (1.3% in Kelvin units) and 15% (0.8% in Kelvin units), compared with cases before wettability alteration. The experimental outcomes also showed that reducing the solvent adsorption on clays in Berea sandstone lowers the nucleation temperature of heptane and octane from their normal phase-change temperatures by 20% (4.3% in Kelvin units) and 30% (6.5% in Kelvin units). In comparison with the medium wettability alteration, reducing the solvent adsorption had a greater influence on nucleation temperatures. Such a phenomenon shows that molecule-solid interactions have more control of altering the phase behavior of solvents than of medium wettability.

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