Interfacial Tension Measured at Nitrogen-Liquid and Liquid-Liquid Interfaces Using Model Microemulsions at High-Pressure and High-Temperature Conditions

The interfacial tensions (IFTs) of two different model microemulsion systems were studied at high-temperature and high-pressure (HTHP) conditions at the nitrogen-brine interface. The experimental scope covers the temperature range 25-100 degrees C, and a pressure range from atmospheric to 300 bar, more representative of some reservoir conditions. A nonionic ethoxylated alkyl ether based microemulsion (ME1) and a nonionic sugar based microemulsion (ME2) were selected for this study. ME2 was chosen for its tolerance to high salinity and temperature. Favorable interactions between the microemulsions and nitrogen lead to substantial IFT reduction. Low IFT values of 14.36 and 13.1 mN m(-1) were measured for ME1 and ME2, respectively, at the highest temperature and pressure settings, far below the IFT value measured for nitrogen-brine with no microemulsion (40.2 mN m(-1)). Both microemulsions (ME1 and ME2) maintained their IFT lowering capabilities far beyond their respective cloud points. No loss of IFT lowering performance or surfactant phase separation was observed over the studied temperature and pressure ranges. The IFT between 0.2 vol % ME2 and a crude oil was also measured at HTHP conditions. ME2 demonstrated phase stability at the crude oil interface up to 80 degrees C and retained its IFT lowering performance at even higher temperatures. ME2 reduced interfacial tension at the crude oil-brine interface to values of 0.2-0.5 mN m(-1), without any measurable adverse effects of pressure and temperature on the IFT.