Effect of Wettability on Vaporization of Hydrocarbon Solvents in Nano Capillaries

Abstract

Tight rock reservoirs have gained popularity and become a subject of great interest due to their huge recovery potential. A substantial portion of the potential hydrocarbon could be removed from the reservoir by injecting solvent gases (hydrocarbon or CO2) as an Enhanced Oil Recovery (EOR) application. Achieving a precise modeling of these processes and accurate description of hydrocarbon dynamics requires a clear understanding of phase-change behaviour in confined (capillary) medium. It was previously shown that early vaporization of liquids could occur in channels that were larger than 1000 nanometers. 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 macro (> 1000 nm) and nano (< 500 nm) channels 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 closely 13%, on average. Altering rock wettability characteristically changes the average hydrocarbon nucleation temperatures being as critical as the pore size. 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 30%.

Phase behavior of single and multi-component liquid hydrocarbons in real reservoir rocks

“…As a result, shifted vaporization pressures of propane, heptane, and octane were noticed in the permeable rocks, including the tight rocks (shale and tight sandstone) at which a high percentage of their pore diameters are in nanoscale (< 100 nm). This paper is a continuation of our previous works [5][6][7]18,20 , and it investigates the vaporization temperature of pure-component hydrocarbon solvents, binary mixtures, and ternary mixtures in different reservoir rocks and under various pressures. Experimental data and evidences are provided as to the effect of confined environment (nano-pores and high capillary pressures) on the phase behavior (vaporization) of solvents.…”

“…The correct estimation of temperature is beneficial in reducing the operational cost by eliminating the need for excessive heat energy. Pore size distribution analysis (PSDA) was conducted previously in our prior works [6][7][8][9][10][11][12][13][14][15][16][17][18] to experimentally measure the distribution of pore sizes in several reservoir rocks. These studies showed that nearly 4.5% of the pore volume in permeable rocks (Berea sandstone and Indiana limestone) are of nano-size, despite their relatively high permeabilities.…”

“…The issue becomes more critical in tight reservoirs (shale, tight sandstone, etc.) since such rocks are mainly governed by nanopores 17,18 . Shifted phasealteration temperatures and pressures of fluids become observable once the medium sizes go below 1000 nm (nm) as stated by the classical Kelvin equation 19 or 100 nm as reported by Cui et al 15 .…”

“…In a previous study 18 , pore size distribution analysis was performed to identify the deviation of pore sizes in shale, tight sandstone, Indiana limestone, and Berea sandstone. The analysis showed that around 4% of the channels in the permeable rocks (sandstone and limestone) were smaller than 100 nm.…”

“…In our previous studies [6][7][8][9][10][11][12][13][14][15][16][17][18] , PSDA was performed to measure deviation of pore sizes in Berea sandstone, Indiana limestone, tight sandstone, and shale. The study showed several measured parameters including occupation percentage of pores tighter than 1000 nm in each rock.…”