Study On Disposal Scheme And Reinjection Optimization Of Produced Gas In CO₂ Flooding

Injecting CO₂ into the reservoir can not only increase the oil and gas recovery,but also realize the CO₂ geologic storage,which has economic and environmental benefits.However,the primary storage efficiency of CO₂ is less than 50%.In order to improve the utilization efficiency of CO₂,it is necessary to dispose and recycle the associated CO₂ in produce gas.In this paper,the general rule of CO₂-associated gas produced during CO₂ flooding was analyzed.The feasibility and application range of three production gas disposal options were evaluated,including direct re-injection or mixed with pure CO₂ for re-injection,combustion for power generation associated with flue gas re-injection,and CO₂ capture for reinjection.The preliminary screen criteria for these gas disposal options were established.Further,four different CO₂ capture techniques are also compared in terms of applicability and economy,including chemical absorption,low-temperature fractionation,pressure swing adsorption and membrane separation,of which the best CO₂ capture separation process was selected.Six kinds of adsorbent were selected to measure the adsorption equilibrium isotherms of CO₂ and CH₄,the influence of various factors,such as temperature,pressure,gas composition,and CO₂ content on the CO₂ separation were analyzed.And the damage rate of the moisture and oil content to the adsorbent was evaluated.Based on numerical simulation and experimental results,detailed design of CO₂ capture and reinjection process and direct/blending associated gas reinjection were carried out.Finally,an economic model for CO₂ associated gas treatment was established.Based on the characteristics of gas production,a technical and economic evaluation of the above-mentioned scheme was conducted.The research results show that for the CO₂ flooding project in the target block of Xinjiang Oilfield,the direct/blending re-injection scheme is mainly considered.When the CO₂ content is less than 70%,consider the blending re-injection scheme;when the CO₂content is between 70%and 90%,separating reinjection scheme or blending reinjection schemes are adopted;when the CO₂ content is greater than 90%,the direct reinjection scheme is selected.Process optimization results show that PSA has the characteristics of low energy consumption,high purity and wide range of CO₂ concentration,so it's recommended as the best choice.Under the condition that the initial gas CO₂ content of 50%,the temperature of20?and the pressure of 2.5MPa,the selectivity of 13X for the mixed gas is 25 respectively.The moisture and oil content tremendously weakened separation performance of zeolites.Under the conditions of temperature 20?,pressure 2.5MPa,10%water content and 10%oil content,the adsorption amount decreases by 32%and 78%respectively,and the selectivity decreases 48%and 78%.The results of economic evaluation indicate that the CO₂ capture cost is 167 yuan/ton,and the CO₂ capture and reinjection cost is 243 RMB/ton.The reinjection cost of CO₂ is 138 RMB/ton by direct/blend reinjection scheme.