| Summary: | CO<sub>2</sub> enhanced oil recovery (CO<sub>2</sub>-EOR) technology is a competitive strategy to improve oil field economic returns and reduce greenhouse gas emissions. However, the arbitrary emissions or combustion of the associated gas, which mainly consists of CO<sub>2</sub> and CH<sub>4</sub>, will cause the aggravation of the greenhouse effect and a huge waste of resources. In this paper, the high-performance facilitated transport multilayer composite membrane for CO<sub>2</sub>/CH<sub>4</sub> separation was prepared by individually adjusting the membrane structure of each layer. The effect of test conditions on the CO<sub>2</sub>/CH<sub>4</sub> separation performance was systematically investigated. The membrane exhibits high CO<sub>2</sub> permeance of 3.451 × 10<sup>−7</sup> mol·m<sup>−2</sup>·s<sup>−1</sup>·Pa<sup>−1</sup> and CO<sub>2</sub>/CH<sub>4</sub> selectivity of 62 at 298 K and 0.15 MPa feed gas pressure. The cost analysis was investigated by simulating the two-stage system. When the recovery rate and purity of CH<sub>4</sub> are 98%, the minimum specific cost of separating CO<sub>2</sub>/CH<sub>4</sub> (45/55 vol%) can be reduced to 0.046 $·Nm<sup>−3</sup> CH<sub>4</sub>. The excellent short-to-mid-term stability indicates the great potential of large industrial application in the CH<sub>4</sub> recovery and CO<sub>2</sub> reinjection from oilfield associated gas.
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