The key challenge in shale oil development lies in displacing crude oil trapped by capillary forces within nanoscale pore throats. This study overcomes the limitations of conventional fracturing fluids by successfully developing a novel Winsor III microemulsion fracturing fluid system, Gulong-1 (GL-1). The GL-1 system achieves synergistic effects under Gulong shale reservoir conditions due to its unique molecular design. This system exhibits ultralow interfacial tension (10−2 mN/m) and a significant change in wettability characterized by a contact angle reduction from 102.2° to 54.2°, thereby transforming the capillary pressure from flow resistance into driving force for imbibition. Experimental results demonstrate that the GL-1 system achieves an imbibition recovery efficiency of 54.6%. The developed GL-1 system significantly improves oil mobilization and production through the multiscale synergistic mechanism involving the solubilization of the middle-phase microemulsion, wettability alteration, and dynamic phase transitions. Field tests confirmed that this system enables commercial oil production with an extremely low flowback ratio (1%). The required production pressure difference can be reduced by more than 60%. Gas chromatography of the produced oil exhibited a unique distribution with two peaks, providing molecular-level evidence for the chemical promotion mechanism. Numerical simulation forecasts a cumulative oil production exceeding 25 000 cubic meters over a 10-year period through the application of GL-1. This work reveals the multiscale mechanism through which the middle-phase microemulsion regulates the interfacial behavior of shale oil, offering technical support for optimizing shale oil development strategies.
Wu et al. (2026) studied this question.