Objective Anionic-nonionic surfactants have the ability to change the wettability of rock surface, but their ability to reduce oil-water interfacial tension is limited. Therefore, a cosurfactant is compounded to achieve synergistic regulation of oil-water and oil-solid interface, aiming to solve the difficulty of residual oil development.
Method Through the Williamson etherification reaction, a sulfonic acid group was introduced into the nonionic surfactant lauric acid diethanolamide to synthesize an enhanced wetting-regulated cosurfactant—lauric acid ethanolamide sulfonate (HLDEA). With the reduction of oil-water interfacial tension as the index, the surfactant nonylphenol polyoxyethylene ether sodium sulfate (NPES) was compounded to obtain the best enhanced wetting high-efficiency oil displacement system. The oil-water interfacial tension reduction performance, wetting control performance, oil film peeling performance and oil displacement performance were evaluated.
Result The 0.3 wt% HLDEA+NPES system could reduce the oil-water interfacial tension to 3.8×10−3 mN/m, which achieved ultra-low interfacial tension. Meanwhile, HLDEA and NPES molecules could be adsorbed to the surface of lipophilic rock, and the underwater oil contact angle increased from 41.34° to 162.53°, which regulated the surface of hydrophobic rock to a strong underwater oleophobic state. At 75 ℃, the oil film area on the surface of the slide was reduced by 75.3% after HLDEA+NPES system treatment for 24 h, and the overall peeling of the oil film was realized.
Conclusion The results of indoor core dynamic oil displacement experiments showed that HLDEA+NPES system could increase the recovery rate to 63.60%, which increase by 28.74 percentage points on the basis of water flooding and 7.80 percentage points on the basis of ultra-low interfacial tension system flooding. The HLDEA+NPES system can simultaneously achieve ultra-low interfacial tension and wetting control of rock surfaces, which has practical application potential.
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