Oil & Gas Geology ›› 2024, Vol. 45 ›› Issue (2): 553-564.doi: 10.11743/ogg20240218

• Methods and Technologies • Previous Articles     Next Articles

Advances in research on CO2 replacement for natural gas hydrate exploitation

Mingxing BAI1,2(), Zhichao ZHANG1,2(), Qiaozhen CHEN3, Long XU4, Siyu DU1,2, Yexin LIU1,2   

  1. 1.Northeast Petroleum University,Daqing,Heilongjiang 163318,China
    2.Key Laboratory of Enhanced Oil Recovery (Northeast Petroleum University),Ministry of Education,Daqing,Heilongjiang 163318,China
    3.Daqing Normal University,Daqing,Heilongjiang 263311,China
    4.Yixin Coal Mine,Hegang Branch of Heilongjiang Longmei Mining Co. ,Ltd. ,Hegang,Heilongjiang 154100,China
  • Received:2023-09-12 Revised:2024-03-19 Online:2024-04-30 Published:2024-04-30
  • Contact: Zhichao ZHANG E-mail:bai510714@163.com;1209712605@qq.com

Abstract:

The application of CO2 replacement method to develop natural gas hydrates (NGHs) is considered a highly promising technology for enhancing both CH4 recovery and CO2 sequestration. This study presents a review of the replacement mechanisms with CO2 and its mixed gas for NGH exploitation, as well as technological advances in the replacement with CO2 mixed with N2/H2 and geothermal-assisted CO2 replacement for enhancing CH4 recovery from NGHs. Key findings are as follows: (1) To replace NGHs with pure CO2 yields a low CH4 recovery. In contrast, injecting CO2 mixed with N2/H2 at varying ratios into NGH reservoirs proves effective in enhancing CH4 recovery. (2) Injecting CO2 mixed with N2 or H2 into NGH reservoirs can reduce the Van der Waals’ forces between CH4 molecules and NGHs’ molecular cages through the competitive adsorption among various gas molecules. Furthermore, it can decrease the partial pressure on the CO2 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 CO2 hydrates during the replacement process and mitigate the adverse effects of hydrate encapsulation, thus enhancing CH4 recovery. (3) Injecting CO2 mixed with N2 for NGH exploitation can reduce the adverse effects of hydrate encapsulation. However, the newly formed N2 hydrates can block the pathways through which CO2 molecules enter the molecular cages of NGHs, thus leading to limited performance in enhancing CH4 recovery. (4) Unlike CO2 and N2, H2 does not form new hydrates under the conditions of hydrate reservoirs. Furthermore, competitive adsorption will occur between H2 and N2 when a minor amount of H2 is injected, further curbing the formation of N2 hydrates. Therefore, introducing H2 of low concentration to mixed CO2-N2 gas can further increase the displacement rate of CH4 in NGHs, thus boosting the CH4 recovery, establishing it as a crucial method to enhance the performance of CO2 replacement for NGH exploitation. (5) Cyclic injection of mixed gas can significantly enhance both the CH4 recovery from NGHs and the sequestration rate of CO2 hydrates. (6) Geothermal-assisted CO2 replacement for NGH exploitation can not only reduce the encapsulation effect of newly formed CO2 hydrates but also facilitate CO2 sequestration in geothermal and hydrate reservoirs, thereby markedly increasing subsurface CO2 sequestration rate while simultaneously enhancing CH4 recovery.

Key words: phase equilibrium, encapsulation, sequestration rate, recovery, replacement with a mixture of CO2 and N2/H2, CO2 replacement method, natural gas hydrate (NGH)

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