| The study of EOR is one of the eternal themes in oil and gas field development, and EOR by gas injection has become a mature technology to improve oil production. At the later stage of secondary recovery, after the waterflooding development of reservoir, the water content will gradually rise and the coverage of water flood will decrease, which is no longer suitable for further waterflooding development.After nearly 40 years of development, the degree of reserve recovery of crude oil in KeKeYaX52 volatile oil reservoir is low, just 21.5%, the oil recovery by water flooding is low. The crude oil here is volatile oil, which is light and will be deaerated easily. And the reservoir have edge water. The water content of reservoir will rise very soon after waterflooding. As the reservoir has been in the condition of high water content, there are great limitations for the other ways of EOR.This paper evaluated the feasibility of hydrocarbon gas injection in Lunnan Oil Field based on the present development status of KeKeYaX52 volatile oil reservoir. X52 volatile oil reservoir has many layers and large span. The geological conditions of it are complex and the physical difference of fluid and core between each block are great. But the natural gas resource of this oil field is very rich, so hydrocarbon gas injection flooding has a good application prospect in this reservoir. Therefore, doing feasibility of EOR by hydrocarbon gas injection in X52 volatile oil reservoir is researched, combined with the indoor hydrocarbon gas injection experiment and numerical simulation method.The oil in surface separator, natural gas sample and reservoir core sample are obtained from the scene of K233 well in X52 oil reservoir. Formation water is prepared according to the related analysis. Then the research begins. According to the PVT physical experiment on these samples, the gas oil ratio is 363.12 and the bubble point pressure is 36.14MPa. Through the gas injection expansion experiment, the result shows that when the molar volume percentage of injected gas volume reaches to 60.397%, the expansion coefficient is the biggest. Choosing 15 pieces of core whose permeability are good,6 groups of long core displacement experiments are made by the way of direct gas drive flooding, water alternating gas flooding, improving the pressure to 25 MPa?improving the pressure to 39.4 MPa, improving the pressure for once and improving the pressure by stages. Experimental results show that the oil recovery can be enhanced the most drastically by taking the exploitation way of improving pressure firstly to 39.4MPa and water alternating gas flooding followed after the natural depletion,the cumulative recovery degree is 83.15%.Based on the whole reservoir component model of KeKeYaX52 volatile oil reservoir, through numerical simulation of the profile model of injection and production well groups extracted, the oil displacement efficiency differences of different displacement ways are considered. And in the light of different displacement ways, the simulation results show that: by taking the water alternating gas flooding after waterflooding, the crude oil recovery degree is 24.48%, which increases by 2.42% in relation to the crude oil recovery degree of that displacement method, taking gas injection continuously after waterflooding. By simulating the oil displacement efficiency under different raise pressures, the results show that:after waterflooding, by improving the pressure to 39.4 MPa in advance, the cumulative recovery degree of crude oil is the highest,28.34%; by improving the pressure to 25.4 MPa in advance, the cumulative recovery degree of crude oil,24.91%, takes second place. The results of numerical simulation are coincident with that of indoor experiment.EOR by hydrocarbon gas injecting in KeKeYa X52 volatile oil reservoir is feasible. Increasing the pressure to 39.4 MPa after waterflooding and then taking the water alternating gas flooding is the most suitable development mode for this reservoir. |
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