Abstract:

The foam drainage gas recovery technique in natural gas production is widely recognized as the most cost-effective and efficient method for removing the water accumulated at the well bottom, which is an essential measure to ensure stable production for low-pressure and low-productivity gas wells. However, the bottomhole liquids are often contaminated by condensate oil, resulting in reduced effectiveness of conventional foaming agents. In this work, the foam properties of eight surfactants were investigated and the effects of oil content and temperature on their foam properties were also examined. The zwitterionic surfactant CAB, which demonstrated relatively good resistance to oil, was selected as the primary component of the foaming agent. By combining CAB with a fluorocarbon surfactant and a foam stabilizer, a new anti-condensate oil foaming agent SCU-7 was developed. The flowability, foaming performance at different oil content, and the foaming performance under simulated high-temperature and high-pressure conditions at the bottom were analyzed to explore the anti-oil mechanism of SCU-7. The results showed that, at 60 ℃ under atmospheric pressure, with an oil content of 10%, a concentration of 0.3% SCU-7 achieved the foam height of 167 mm in simulated saline water with total salinity of 4×10⁴ mg/L; the foam height was 135 mm at 3 min; after 15 min, the liquid-carrying capacity was up to 206 mL, demonstrating excellent overall performance. However, when the oil content was increased to 30%, the overall foaming performance declined to some extent. Under high pressure of 6 MPa and at temperatures of 80 ℃, 100 ℃ and 120 ℃, SCU-7 could generate dense foams in simulated saline water. Mechanism analysis indicated that CAB exhibited excellent ability of surface tension reduction in simulated saline water; mixing CAB with fluorocarbon surfactant could further decrease surface tension, while the presence of foam stabilizer could enhance the strength of foam film and thus improve foaming performance. Therefore, SCU-7 demonstrated good foaming performance with improved anti-oil properties.

Key words: foaming agent, surfactant, foaming performance, anti-condensation oil