An experimental study of interfacial tension and contact angles of CO₂/brines/surfactants/oil systems with dolomite rock

In this work the effects of different parameters such as surfactant type, salinity, temperature, pressure and oil type have been studied experimentally in the presence of CO₂ at 30°C and pressures as high as 5000 psi for changes in interfacial tension and wettability with dolomite rock. In the 1st step, IFT of four multicomponent brines of different salinities were compared and the brine showing lowest IFT with CO₂ was used in the 2nd step for comparison of three different brine-surfactant solutions (BSS). The BSS with lowest IFT was then used to study the IFT behavior of three different oils with CO₂. Last step consists of contact angle(CA) measurements of oil with dolomite rock in the presence of CO₂and BSS. Brines are multicomponent with salinities ranging from 8,500 to 67,000 ppm. Comparison of surfactants was among solutions of an alcohol-propoxysulfate surfactant, a viscoelastic surfactant and a fluorosurfactant. IFT of brines increase with increase in salinity and temperature and decreases with increase in pressure. This is due to solubility of CO₂ in brine. Out of the three surfactants, most soluble solution is a fluorosurfactant and gives ultra-low IFT with CO₂. This BSS of florosurfactant when used with oil, forms pressure-sensitive microemulsions in CO₂ causing the IFT of the oil to decrease. CA of oils with dolomite rock increase with pressure in the presence of fluorosurfactant and CO₂. In the literature, comparison of IFTs of different surfactants in CO₂-Brine systems, Brine-Oil systems, Surfactant-CO₂systems, and surfactant-oil systems have been reported but this work reports on all CO₂/Brine/Surfactant/Oil/Dolomite co-existing which can help in planning a Surfactant-Alternating- Gas(SAG) or Water-Alternating-Gas(WAG) process more accurately.