Study on the variation law of the water-cut of low-permeability low-saturation sandstone reservoirs in water displacing oil

Two types of physical simulation experiments of water displacing oil with different initial oil saturation are carried out in order to study the characteristics of water flooding in low-permeability and low-oil-saturation sandstone reservoir.The water-cut variation law with injected pore volume multiple is obtained,and the mechanism of the water-cut variation is analyzed according to both pore structure and oil-water distribution of the reservoir.A general empirical formula for the water-cut variation curve is obtained by curve fitting,the effects of the coefficients in the formula on the feature of the water-cut curve are analyzed,and the relationships between these coefficients and relevant parameters of reservoir are presented.The results indicate that during water flooding in low-permeability and low-oil-saturation reservoir,there is neither starting pressure gradient nor water-free oil production period,and the water cut increases rapidly in the first stage,decreases in the middle stage and then increases gradually to a steady state.