Study on characteristics, efficiency, and variations of water flooding in different stages for low permeability oil sandstone

Water flooding is an important way to improve recovery in low-permeability sandstone oil reservoirs. How to decouple the water flooding process using dynamic and static information is a hot topic. In this paper, taking the Paleocene low-permeability oil sandstone, BY area, eastern Nanxiang Basin as an example, the microscopic water flooding process in the low-permeability sandstone matrix was systematically investigated, and the characteristics of water channeling under the conditions of fracture existence were analyzed using the dynamic and static monitoring data. The results show that the target layer mainly develops frequently thin stacked composite sand bodies. Under the combined influence of matrix and fracture seepage, the low-permeability sandstone developed by water flooding shows that there is a single direction of efficiency. The direction of advantageous water advancement is 45° north–east, and the speed of water flooding advancement is 2.57 m/day. Microscopic water-drive oil experiments show that bound water is mainly distributed in the original low-permeability sandstone as a membrane in the pore wall and as short rods in the throat. Differences in pore structure and petrophysical properties affect the residual oil content and degree of oil recovery. For sandstones with good petrophysical properties, mild water flooding can improve crude oil recovery. The increase in oil production is mainly concentrated in the early stage of water flooding development, and the increase in oil recovery degree is not significant with the increase in injection multiples in the middle and late stages. However, for sandstones with relatively poor petrophysical properties, water flooding is more effective in the early and late stages than in the middle stages. Therefore, it is necessary to adjust the water flooding measures according to the differences in the petrophysical properties of the sand body. Local tectonics and natural fracture strikes are important factors affecting the direction of the expansion of water flooding fractures. Overall, the prevention of water channeling in low-permeability sandstones has to take into account the complex coupling between water flooding fractures, natural fractures, and hydraulic fractures.