Study on enhanced oil recovery improvement of fractured tight reservoir at extra high water cut stage

The objective of this study is to examine methods for improving the recovery rate in low-permeability fractured tight oil reservoirs during the special high-water stage. Three oil-soluble surfactants and anionic surfactants were tested using oil, water, and cores. The study employed surfactant performance tests, dynamic oil washing rate analyses, interfacial tension analyses, and core oil displacement tests to analyze the surfactant-enhanced oil recovery mechanism. Results revealed that the oleic acid diethanolamide (ODEA) surfactant system, when mixed with anionic surfactants, demonstrated superior water separation, oil washing, and adsorption performance. This system increased oil recovery by over 46% during the ultra-high water cut period. Additionally, numerical simulations indicated that crude oil recovery is influenced by wettability, fracture density, and crude oil viscosity during the ultra-high water cut stage in fractured tight reservoirs.