Simulation And Experimental Study On Multi-stage Memrane Separation Process Of Associated Gas In Oilfild

CO₂displacement and enhanced oil recovery(CO₂-EOR)has become a common method to enhance oil recovery in the petroleum industry.However,the associated gas produced in the process of CO₂flooding contains a large amount of CO₂,CH₄and other gases,which will not only pollute the environment but also cause a huge waste of resources if discharged directly.On the contrary,the separated and purified CO₂can be reused for oil displacement,and CH₄can be used as fuel gas to realize the resource utilization of associated gas.Obviously,it is necessary to study the separation technology of associated gas.Membrane separation has the advantages of small volume and compact structure,which is very suitable for associated gas processing of exploration oil Wells.Combining with the characteristics of associated gas,the membrane separation process can be designed to recover two kinds of high purity CO₂and CH₄gas,and the selection of appropriate gas separation membrane material is the key to promote the large-scale application of gas membrane separation process in industry.In this paper,a gas separation membrane process including pre-treatment was designed in view of the characteristics of large variation in component content and flow rate of CO₂-EOR associated gas in an oilfield.After this process,high-purity CO₂and CH₄product gas could be collected from the permeable side and the retentate side of the membrane respectively.A counter current hollow fiber membrane model was established,and the separation process of hollow fiber membrane was simulated by MATLAB Simulink.The separation characteristics and separation effects of polyimide(PI),cellulose acetate(CA)and polysulfone(PSF)membrane materials were compared under different operating conditions.The results showed that PI had the best comprehensive separation effect.Considering the complexity of multi-stage membrane process design,this paper designed three multi-stage membrane separation processes for CO₂/CH₄/N₂using Aspen HYSYS system,and investigated the purity and recovery of CO₂and CH₄,as well as the energy consumption and total unit cost of the compressor under the conditions of 30%,50%and 70%feed gas CO₂concentration.The results show that the two-stage two-step process can accomplish the separation task better,and the total unit cost is0.0187$/Nm~3CH₄.The effects of feed gas concentration,flow rate and operating pressure on the separation process were studied.Finally,a commercial PI membrane was used to separate the associated gas,and the effects of temperature,pressure and stage-cut on the separation traits were investigated.The results show the efficiency is better when the temperature is 35?50?,the pressure is 0.7?1.0MPa and the stage-cut is 0.4?0.55.With the increase of stage-cut,the separation coefficients of CO₂/CH₄and CO₂/N₂increased.The experimental results are in good agreement with the simulation results of MATLAB and HYSYS,and the relative errors are less than 4%and 8.7%,respectively.