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A thermodynamically stable interface can only exist between two immiscible fluids, nonetheless in this work an “immiscible interface” between two gases (CO2–methane) has been observed and is documented within this paper. This work is the first ever attempt to measure the interfacial tension (IFT) in a gas–gas system, the interfacial tension of supercritical carbon dioxide (SCO2–methane) was measured at temperatures of 368.15 and 433.15 K and pressures between 6.9 and 41.37 MPa, using a modified pendant drop method. This study was undertaken to investigate the effects of CO2 injection into a gas reservoir or enhanced gas recovery. It was noted that the IFT decreased linearly with both temperature and pressure in the low-pressure range, but was less sensitive at higher pressures. There was a zone in the vicinity of 10.34 MPa and above that was noted to be independent of temperature where IFT increased very sharply. The IFT was almost threefold higher at 20.69 MPa, for the same temperature, compared with 10.34 MPa. This is attributed to the density of SCO2 at 10.34 MPa being less than 1/3 of density at 20.69 MPa, at the same temperature. It was also evident that the SCO2–methane IFT was relatively lower at higher temperature; a behavior seen in density and viscosity of SCO2. The IFT results at 41.37 MPa and 433.15 K were very close to the 20.69 MPa and 368.15 K. The increase in temperature slightly influenced IFT and was matched by the pressure effect on IFT. Hence the overall impact remained almost the same. |
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