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<p>The competitive adsorption of CH<sub>4</sub>/CO<sub>2</sub> in shale has consistently garnered significant attention as a means to enhance the recovery efficiency of shale gas reservoirs. A theoretical formula for a binary gas competitive adsorption rate model was formulated to investigate the adsorption and desorption characteristics and the evolution patterns of carbon dioxide (CO<sub>2</sub>) displacing methane (CH<sub>4</sub>) in shale. This formula was integrated into the lattice Boltzmann method (LBM) to simulate the displacement process of CH<sub>4</sub> by CO<sub>2</sub>, addressing competitive adsorption challenges associated with binary gases exhibiting adsorption/desorption behaviors. The research findings reveal that the proposed theoretical model accurately captures the competitive adsorption dynamics between CO<sub>2</sub> and CH<sub>4</sub>, elucidating the patterns of adsorption and desorption characteristics during the displacement of CH<sub>4</sub> by CO<sub>2</sub>. This insight is pivotal for understanding the microscopic mechanisms underlying CO<sub>2</sub>-induced CH<sub>4</sub> displacement. The displacement process is dynamic, marked by concurrent adsorption and desorption of CO<sub>2</sub> and CH<sub>4</sub>, ultimately converging to an equilibrium state where CO<sub>2</sub> adsorption and CH<sub>4</sub> desorption coexist. Notably, the time taken for CO<sub>2</sub> to attain equilibrium is marginally delayed compared to CH<sub>4</sub>. Moreover, the concentration of injected CO<sub>2</sub> substantially influences the dynamics of CO<sub>2</sub> replacing CH<sub>4</sub>, as the CO<sub>2</sub> injection concentration increases, both the adsorption rate of CO<sub>2</sub> and the desorption rate of CH<sub>4</sub> augment, while the time required to reach equilibrium in the adsorption/desorption process diminishes. This implies that CO<sub>2</sub> injection effectively facilitates CH<sub>4</sub> desorption. Additionally, models with higher porosity exhibit enhanced permeability, resulting in accelerated adsorbate diffusion rates and improved displacement efficiency. The heterogeneity of the pore structure exerts a pronounced impact on the velocity distribution within the flow field, which in turn significantly influences the concentration field distribution of CO<sub>2</sub> and CH<sub>4</sub>. It is worth noting that the distribution characteristics of the two gases within the flow field and their concentrations within the particles are complementary. The results underscore that carbon dioxide injection can enhance methane desorption, thereby improving shale gas recovery.</p>

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Study on CO2/CH4 displacement process in shale microscale models with adsorption/desorption behavior by lattice Boltzmann method

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月12日

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  • Yifu Zhang,
  • Yu Xu,
  • Xuefeng Chen,
  • Zikun Pi,
  • Qiannan Xie,
  • Kunpeng Liao

摘要

The competitive adsorption of CH4/CO2 in shale has consistently garnered significant attention as a means to enhance the recovery efficiency of shale gas reservoirs. A theoretical formula for a binary gas competitive adsorption rate model was formulated to investigate the adsorption and desorption characteristics and the evolution patterns of carbon dioxide (CO2) displacing methane (CH4) in shale. This formula was integrated into the lattice Boltzmann method (LBM) to simulate the displacement process of CH4 by CO2, addressing competitive adsorption challenges associated with binary gases exhibiting adsorption/desorption behaviors. The research findings reveal that the proposed theoretical model accurately captures the competitive adsorption dynamics between CO2 and CH4, elucidating the patterns of adsorption and desorption characteristics during the displacement of CH4 by CO2. This insight is pivotal for understanding the microscopic mechanisms underlying CO2-induced CH4 displacement. The displacement process is dynamic, marked by concurrent adsorption and desorption of CO2 and CH4, ultimately converging to an equilibrium state where CO2 adsorption and CH4 desorption coexist. Notably, the time taken for CO2 to attain equilibrium is marginally delayed compared to CH4. Moreover, the concentration of injected CO2 substantially influences the dynamics of CO2 replacing CH4, as the CO2 injection concentration increases, both the adsorption rate of CO2 and the desorption rate of CH4 augment, while the time required to reach equilibrium in the adsorption/desorption process diminishes. This implies that CO2 injection effectively facilitates CH4 desorption. Additionally, models with higher porosity exhibit enhanced permeability, resulting in accelerated adsorbate diffusion rates and improved displacement efficiency. The heterogeneity of the pore structure exerts a pronounced impact on the velocity distribution within the flow field, which in turn significantly influences the concentration field distribution of CO2 and CH4. It is worth noting that the distribution characteristics of the two gases within the flow field and their concentrations within the particles are complementary. The results underscore that carbon dioxide injection can enhance methane desorption, thereby improving shale gas recovery.