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<p>N<sub>2</sub>/CO<sub>2</sub> flooding coalbed methane storage technology is an effective technology to improve coalbed methane recovery and CO<sub>2</sub> geological storage at the same time. In this paper, considering the influence factors such as heat conduction and coal deformation, the characterization volume element method is used to describe the adsorption, desorption and seepage of ternary gas in coal and the related changes caused by coal matrix. The coupling model of N<sub>2</sub>, CO<sub>2</sub> and CH<sub>4</sub> ternary gas displacement adsorption is established, and the reliability of the model is verified. The results show that CO<sub>2</sub> is the main reason to strengthen CH<sub>4</sub> production. Simple CO<sub>2</sub> injection has a significant adsorption and expansion effect on coal body, and high-pressure N<sub>2</sub> gas is needed to drive CO<sub>2</sub> to migrate to the far field of coal body. However, too high N<sub>2</sub> gas injection ratio is more likely to lead to production well breakthrough, which reduces the recovery rate of CH<sub>4</sub>. The higher the proportion of CO<sub>2</sub> injection, the greater the total adsorption heat released, and the larger the range of coal temperature rise. When the proportion of CO<sub>2</sub> injection is too low, the temperature near the injection well first decreases slightly and then increases rapidly due to the combined effects of gas expansion cooling and CO<sub>2</sub> adsorption heat release. The permeability ratio on the route from the injection well to the production well increases rapidly and then decreases slowly. The lower the CO<sub>2</sub> injection ratio, the farther away from the injection well, the lower the permeability of the coal body. However, with the increase of CO<sub>2</sub> injection ratio, the permeability of the coal body shows a trend of increasing first and then decreasing. When the CO<sub>2</sub> injection ratio increases to 60%, the change trend of permeability ratio at different injection time is highly similar. After that, it is necessary to increase the injection ratio of N<sub>2</sub> to drive CO<sub>2</sub> to migrate to the far field coal body. Considering the recovery rate of CH<sub>4</sub> and the storage effect of CO<sub>2</sub>, 60% CO<sub>2</sub> + 40% N<sub>2</sub> is the best injection ratio. This study provides a theoretical basis for optimizing the N<sub>2</sub>/CO<sub>2</sub> mixed injection ratio to balance CH<sub>4</sub> recovery and CO<sub>2</sub> storage in coalbed methane reservoirs, supporting sustainable energy development and greenhouse gas emission reduction.</p>

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Simulation study on nonlinear permeability characteristics of coalbed methane mining driven by mixed N2/CO2 pressure

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月19日

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  • Yanjiao Li,
  • Yang Wang,
  • Yu Xiong,
  • Yujia Xiao

摘要

N2/CO2 flooding coalbed methane storage technology is an effective technology to improve coalbed methane recovery and CO2 geological storage at the same time. In this paper, considering the influence factors such as heat conduction and coal deformation, the characterization volume element method is used to describe the adsorption, desorption and seepage of ternary gas in coal and the related changes caused by coal matrix. The coupling model of N2, CO2 and CH4 ternary gas displacement adsorption is established, and the reliability of the model is verified. The results show that CO2 is the main reason to strengthen CH4 production. Simple CO2 injection has a significant adsorption and expansion effect on coal body, and high-pressure N2 gas is needed to drive CO2 to migrate to the far field of coal body. However, too high N2 gas injection ratio is more likely to lead to production well breakthrough, which reduces the recovery rate of CH4. The higher the proportion of CO2 injection, the greater the total adsorption heat released, and the larger the range of coal temperature rise. When the proportion of CO2 injection is too low, the temperature near the injection well first decreases slightly and then increases rapidly due to the combined effects of gas expansion cooling and CO2 adsorption heat release. The permeability ratio on the route from the injection well to the production well increases rapidly and then decreases slowly. The lower the CO2 injection ratio, the farther away from the injection well, the lower the permeability of the coal body. However, with the increase of CO2 injection ratio, the permeability of the coal body shows a trend of increasing first and then decreasing. When the CO2 injection ratio increases to 60%, the change trend of permeability ratio at different injection time is highly similar. After that, it is necessary to increase the injection ratio of N2 to drive CO2 to migrate to the far field coal body. Considering the recovery rate of CH4 and the storage effect of CO2, 60% CO2 + 40% N2 is the best injection ratio. This study provides a theoretical basis for optimizing the N2/CO2 mixed injection ratio to balance CH4 recovery and CO2 storage in coalbed methane reservoirs, supporting sustainable energy development and greenhouse gas emission reduction.