The EOR Study Of CO₂ Injection In S Reservoir

With the further exploration and development of reservoirs,the proportion of low permeability reservoirs has increased,and the development of low permeability reservoirs is becoming more and more important.Because the low permeability reservoir has the characteristics of low permeability,the absorbing capacity of water injection is low and the development effect is poor.Because CO2 can effectively reduce the viscosity of crude oil,improve the mobility ratio and reduce the interfacial tension,the low permeability reservoirs can be effectively developed by CO2 injection.In this paper,the S low permeability reservoir is used as a research object to study the feasibility of CO2 injection.The fuzzy comprehensive evaluation method is used to analyze the CO2 adaptability of the reservoir.Based on the theory of enhanced oil recovery by gas injection,the feasibility of CO2 flooding is studied by means of reservoir numerical simulation technique,the single water injection model of the reservoir has been changed to achieve efficient and reasonable development of the reservoir.The main findings are as follows:(1)Based on the fuzzy mathematics theory,the fuzzy comprehensive evaluation method is used to judge and analyze the relevant factors affecting the CO2 injection in the reservoir.The weight value of each factor is determined by the analytic hierarchy process,the fuzzy comprehensive evaluation model is established,According to the principle of maximum membership degree,the index value of ’good’ is 0.499 and the S reservoir is suitable for improving the oil recovery by injecting CO2.(2)The characteristics of crude oil phase in the S reservoir are studied,and the crude oil of the S reservoir is simulated by numerical simulation software.The SEPS experiment,the constant composition expansion experiment and the swelling test are fitted.The results show that the fluid parameters which reflect the actual phase characteristics of the fluid can be obtained.(3)The experiment of long core such as kinds of displacement medium experiments,hydrocarbon gas/water alternation experiments and CO2/water alternation experiments are fitted.The results show that CO2 injection is the best,and the smaller the slug size is,the better the displacement efficiency is.(4)Based on the understanding of the geology development characteristics in the S reservoir,the production history match of the reservoir is carried out by numerical simulation software.The effect of continuous injection by four kinds of gas injection media is compared.The effectiveness of different injection rate,different gas-water alternation period and slugging number and injection timing is analyzed.The optimal injection parameters are obtained.Finally,the evaluation method of enhancing oil recovery by CO2 in S reservoir is formed.(5)The research results of this paper not only provide scientific basis for the development of S reservoir,but also provide important reference value for the study of enhancing oil recovery by CO2 in low permeability reservoir.