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黄陵矿区弱黏煤CO2驱替CH4注入压力作用效应及合理阈值研究

Study on the effect of CO2 displacement and CH4 injection pressure and its optimal threshold in weakly caking coal of the Huangling Mining Area

  • 摘要: 针对低渗透煤层瓦斯抽采效率低、CO2驱替技术中注入压力难以界定的问题,以黄陵矿区弱黏煤为研究对象,采用理论研究与实验相结合的方法,系统研究了CO2驱替CH4的注入压力特性及合理阈值。明确了注入压力的双重作用机制,将其划分为基于微观吸附势改变组分吸附态的置换压力,以及基于压力梯度驱动游离态气体运移的驱替压力。基于Langmuir吸附理论计算了不同压力下煤对CO2和CH4的吸附量及置换比,并使用自行搭建的实验装置开展了不同注入压力下的驱替实验。结果表明:弱黏煤的驱替置换过程表现出明显的注入压力敏感性,驱替效率随压力的增大呈现“三段式”增长规律。分析表明,标准化处理后,驱替效率、驱替置换比关于注入压力的变化曲线在3.75 MPa处相交,形成关键临界点。该交点不仅标志着驱替效率进入高效区间,同时也反映了置换单位体积CH4所需的CO2资源成本达到技术经济平衡的最优工况。综合考虑吸附势微观转变拐点、宏观驱替效率及工程经济性,黄陵矿区弱黏煤的合理注入压力阈值为3.8~7.0 MPa。该研究成果为低渗透煤层CO2驱替瓦斯技术的工业化参数设计提供了参考依据与数据支撑。

     

    Abstract: Low-permeability coal seams often have low gas drainage efficiency, and the appropriate injection pressure for CO2-enhanced methane recovery remains difficult to determine. This study investigates the injection pressure characteristics and optimal pressure range for CO2 displacement of CH4 in weak coking coal from the Huangling Mining Area using theoretical analysis and laboratory experiments. The injection pressure was found to have two main effects: it changes the adsorption state of CO2 and CH4 by altering adsorption potential, and it promotes free-gas migration through pressure gradients. Based on Langmuir adsorption theory, the adsorption capacities and displacement ratios of CO2 and CH4 were calculated under different pressures. CO2 displacement experiments were then conducted at varying injection pressures using a self-developed experimental system. The results show that CO2 displacement in weak coking coal is highly sensitive to injection pressure, and the displacement efficiency increases in three stages as pressure rises. After normalization, the curves for displacement efficiency and displacement ratio intersect at 3.75 MPa, indicating a critical point. This point marks the beginning of the high-efficiency displacement range and represents a balance between methane recovery and CO2 consumption. Considering the adsorption transition point, displacement efficiency, and engineering economics, the reasonable injection pressure range for weak coking coal in the Huangling Mining Area is determined to be 3.8-7.0 MPa. These findings provide practical guidance and data support for designing CO2-enhanced methane recovery parameters in low-permeability coal seams.

     

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