Study on Ultimate Recovery Factor and Oil Recovery Rate of Water-Flooded Sandstone Oil Fields in Eastern South China Sea

Abstract

Abstract Under the natural energy development of Marine sandstone oil fields in the east of the South China Sea, the recovery degree of some oil fields has exceeded 65%, and the production capacity is still strong. The high-speed development model does not seem to have an adverse effect on oil recovery. Based on the existing knowledge and technical conditions, it is difficult to analyze and predict the final recovery rate of oil field. The reasonable boundary between the oil rate and recovery is also unclear. In this study, we investigate the correlation between oil rate and recovery rate by experiment and field practice. Based on the microscopic displacement experiment, the variation rules of phase permeability, wettability, residual oil, displacement efficiency and sweep volume of different displacement multiples are studied. The variation law of oil rate and recovery under different fluidity and well control conditions is studied by mathematical statistics according to the production dynamic data. Thus, the influencing factors and percolation mechanism of the optimal recovery under high multiples water flooding are clarified, and the relationship between the reasonable oil rate and optimal recovery under different reservoir conditions is formed. Micro experiments show that high multiples water flooding can improve the reservoir property, change wettability of rocks, reduce the residual oil saturation, improve oil displacement efficiency and the final oil displacement efficiency can reach 80%. Statistical research shows that when the oil recovery rate is less than 10%, the recovery rate increases with the increase of oil rate. For bottom water reservoirs, the recovery rate is recommended to be no more than 8%. The paper innovatively studies the correlation between the reasonable oil rate and optimal recovery in Marine sandstone oilfield from microscopic experimental analysis and macroscopic statistical research. The research results effectively guide the oil field production practice of more than 200 Wells in more than 20 oil fields in the eastern South China Sea in 2019, with a cumulative oil increase of more than 5 million barrels. And it has important guiding significance to the efficient and economical development of Marine sandstone oilfield.