二氧化碳置换法开采天然气水合物研究进展

Advances in research on CO replacement for natural gas hydrate exploitation

柏明星 张志超 陈巧珍 徐龙 杜思宇 刘业新

Mingxing BAI Zhichao ZHANG Qiaozhen CHEN Long XU Siyu DU Yexin LIU

应用CO置换法开采天然气水合物被认为是一种极具潜力的提高CH采收率和CO埋存率的技术。论述了CO及其混合气置换法开采天然气水合物的机理，梳理了CO混N/H及地热辅助CO提高水合物中CH采收率的技术进展。研究表明：①应用纯CO置换开采天然气水合物时，CH的采收率较低，而将CO与N、H以不同比例混合后注入天然气水合物藏中进行CH开采，能够有效提高CH的采收率。②CO与N或H混合注入水合物层时，多种气体分子在竞争吸附作用下降低了CH分子与水合物分子笼之间的范德华力，同时降低了混合气中CO的分压，导致水合物相平衡曲线上移，抑制了置换过程中CO水合物的生成速率，减轻了包裹作用的不利影响，从而提高CH采收率。③CO混合N注入开采水合物时，N的混入虽然能够减轻包裹作用的影响，但新形成的N水合物会堵塞CO进入水合物分子笼的通道，因此提高CH采收率效果有限。④在水合物层条件下H并不会形成新的水合物，而且混入少量的H又会与N发生吸附竞争，从而抑制N水合物的形成，故将低浓度的H气混入CO与N的混合气中能够进一步提高对水合物中CH的置换率，从而提高CH的采收率。因此，混入H被认为是提高CO置换开发水合物效果的重要途径。⑤混合气周期注气方式可明显提高水合物中CH的采收率和CO水合物藏封存率。⑥应用地热辅助CO开采水合物的方法也能够降低新形成水合物的包裹作用，同时实现CO在地热层和水合物层的两次埋存，在提高CH采收率的同时，大大提高CO在地层中的埋存率。

The application of CO replacement method to develop natural gas hydrates （NGHs） is considered a highly promising technology for enhancing both CH recovery and CO sequestration. This study presents a review of the replacement mechanisms with CO and its mixed gas for NGH exploitation， as well as technological advances in the replacement with CO mixed with N/H and geothermal-assisted CO replacement for enhancing CH recovery from NGHs. Key findings are as follows： （1） To replace NGHs with pure CO yields a low CH recovery. In contrast， injecting CO mixed with N/H at varying ratios into NGH reservoirs proves effective in enhancing CH recovery. （2） Injecting CO mixed with N or H into NGH reservoirs can reduce the Van der Waals’ forces between CH molecules and NGHs’ molecular cages through the competitive adsorption among various gas molecules. Furthermore， it can decrease the partial pressure on the CO phase in the mixed gas， resulting in an upward shift in the phase equilibrium curve of NGHs. Such shift can inhibit the generation rate of CO hydrates during the replacement process and mitigate the adverse effects of hydrate encapsulation， thus enhancing CH recovery. （3） Injecting CO mixed with N for NGH exploitation can reduce the adverse effects of hydrate encapsulation. However， the newly formed N hydrates can block the pathways through which CO molecules enter the molecular cages of NGHs， thus leading to limited performance in enhancing CH recovery. （4） Unlike CO and N， H does not form new hydrates under the conditions of hydrate reservoirs. Furthermore， competitive adsorption will occur between H and N when a minor amount of H is injected， further curbing the formation of N hydrates. Therefore， introducing H of low concentration to mixed CO-N gas can further increase the displacement rate of CH in NGHs， thus boosting the CH recovery， establishing it as a crucial method to enhance the performance of CO replacement for NGH exploitation. （5） Cyclic injection of mixed gas can significantly enhance both the CH recovery from NGHs and the sequestration rate of CO hydrates. （6） Geothermal-assisted CO replacement for NGH exploitation can not only reduce the encapsulation effect of newly formed CO hydrates but also facilitate CO sequestration in geothermal and hydrate reservoirs， thereby markedly increasing subsurface CO sequestration rate while simultaneously enhancing CH recovery.

10.11743/ogg20240218