In-depth experimental investigations of low-tension gas technique with methane and live oil in high salinity and high temperature sandstone reservoirs

Abstract Low-Tension gas (LTG), as an emerging technique, attempts to synergize oil desaturation by microemulsion and mobility control via foam, which is an ideal alternative wherever other tertiary recovery techniques are technically limited. Previously, high oil recovery was achieved with proposed formula and novel injection strategy under harsh conditions (190,000 ppm, 85 °C) [53] with N2 and dead oil, which were robust to wide reservoir scenes (0.5 ft/d, 7 md) [54] . Here, more practical field scenarios are examined with methane and live oil for the first time facilitated by auxiliary tests of bulk foam stability, microemulsion viscosities and surfactant retention. Microemulsion phase behaviors are probed for both N2 and CH4 under reservoir pressure (1200 psi, 85 °C) in sequence to distinguish the impacts of pressure and solution gas. Therewith, pressure drop, effluent salinity and oil recovery are recorded to analyze effects of mobility control, gas type (N2 or CH4) and oil condition (dead or live) through multiple corefloodings stepwise. It is found higher pressure and solubilized methane impose limited impacts on current microemulsion phase behaviors. The developed formula and novel injection strategy satisfy the requirements of mobility control and oil desaturation, through the balance between foam stability and relatively low IFT. The surfactant retention is 0.162 mg/g during LTG process. Neither gas type or oil condition exerts discernible influences indicated by similarly high oil recoveries around 90%. The findings here promote the field implementation of this novel technique for both greenhouse gas utilization and enhanced oil recovery.