With the development of oil field water flooding, many oil fields have entered the high water cut stage one after another, and some parts of the actual reservoir have been washed by water drive for many years, so the understanding of traditional oil drive efficiency needs to be improved, and the oil drive efficiency under high multiple displacement needs to be clarified. There are many factors affecting oil displacement efficiency. This paper mainly considers the influence of water displacement PV number, crude oil viscosity, permeability and water displacement velocity (capillary number). In order to reveal the changes of high-power water flooding from macroscopic and microscopic points of view, 21 sets of unsteady water flooding core experiments with water flooding PV number of 1000PV were carried out. Among them, 11 sets were high-power water flooding and measured parameters to calculate high-power phase permeability curves. The other 10 groups were subjected to NMR scanning during high-power water flooding to determine the effects of different permeability, viscosity and water flooding speed on the residual oil utilization of different pore sizes. The right shift ratio of residual oil and the expansion ratio of water phase permeability were selected to characterize the change law of high phase permeability.
The results show that the oil displacement efficiency increases with the increase of water displacement multiple, and the increase of oil displacement efficiency decreases with the increase of water displacement multiple. The oil phases in different pore radius are used, and the displacement efficiency of large holes is higher than that of small holes. With the increase of oil viscosity, the right shift ratio of residual oil in high-power water drive increases, which is 1.11 at low viscosity and 1.29 at high viscosity. With the increase of oil viscosity, the expansion ratio of water phase in high multiple water flooding increases, which is 1.07 at low viscosity and 2.28 at high viscosity. The higher the oil viscosity, the higher the oil potential is in high multiple water flooding. The increment of oil displacement efficiency in the low-viscosity group mainly comes from the large pores with pore radius greater than 20um, and the increment of oil displacement efficiency in the medium-high viscosity group mainly comes from the small pores with pore radius less than 10um. With the increase of core permeability, the right shift ratio of residual oil and the expansion ratio of water phase infiltration decrease, and the lower the permeability, the higher the oil increase potential of high multiple water flooding. The oil displacement efficiency of each pore radius in the low permeability group increased, and the increment of oil displacement efficiency in the high permeability group mainly came from the small hole about 8.62um. After high multiple water flooding, the right shift ratio of residual oil increases with the increase of capillary number, and the oil displacement efficiency is greatly improved at high speed, and the expansion ratio of water phase infiltration increases with the increase of capillary number after high multiple water flooding. High-speed water flooding can improve the water phase flow capacity, and the oil increase potential is lower at low speed. At low speed, the displacement efficiency of each aperture increases, and the increment of small aperture is more for 8.62um. The increment of displacement efficiency under high speed condition mainly comes from the large and medium aperture of 27.75um.
Keywords high multiple water flooding, oil displacement efficiency, NMR scanning