Analysis of Water Flooding Effect in Oil Reservoirs with API Gradual Variety of Crude Oil

In a certain overseas operation block of CNPC, the crude oil is gradually reduced from 19.4 API ° to 8.8 API °. In the early stage of development, the pressure in some areas of the reservoir drops rapidly; because of the relatively high structure and the relatively long distance of edge water, it is difficult to spread to the pressure deficit area in a short time. Therefore, it is urgent to supplement formation energy by water injection. In this paper, through the combination of production performance analysis and numerical simulation, the favorable selection of water injection is determined; considering the structure, interlayer distribution, inter well connectivity, wellbore conditions and other factors, a suggestion of water injection well is proposed; the water injection parameters are optimized by numerical simulation. The results show that the area with fast pressure drop is located in the heavy oil area, with large difference of oil-water mobility ratio. The reservoir is suitable for moderate water injection, and the reasonable injection rate is 5000 bbl/d. After the actual injection, the annual average daily water injection is 4652 bbl/d, and the injection pressure is 1000–1200 psi. The monitoring shows that the water injection mainly affects the low-pressure area, 29 wells are affected, and the types of affected wells are divided into three types: 15 wells increase oil rate; 7 wells decline rate decrease slowdown; 7 wells decline rate increased. The effective scope forecasted by using the numerical simulation is basically consistent with the field monitoring. Through water injection, the average bottom hole pressure of individual well is restored 228 psi, the comprehensive decline of reservoir is reduced from 0.2% to 0.1%, and the recovery rate of reservoir is increased by 0.8%.