Experimental study on post-fracture oil-water displacement mechanism of tight sandstone reservoir with NMR

The oil-water displacement after hydraulic fracturing can increase the oil production and reduce the flowback fluid. The NMR technology is applied to study the oil distribution in the core sample before and after oil-water displacement. The main factors affecting the oil-water displacement efficiency are revealed, and the theoretical basis and reference are provided for the optimization of post-fracturing flowback system in tight reservoirs. The results show that the displaced oil is mainly from small pores, medium pores and macropores. The larger the pore size, the higher the oil-water displacement efficiency. Strong homogeneity of core samples and good pore-throat connectivity are the main reasons for the higher oil-water displacement efficiency. The oil-water interfacial tension is low, and the displacement efficiency is improved. The cleanup additive in guar gum fracturing fluid can effectively reduce the oil-water interfacial tension and improve the oil-water displacement efficiency compared with the slick water fracturing fluid.