瓦斯事故是煤矿安全生产的主要威胁之一，瓦斯主要成分为CH₄。CO₂是造成全球温室效应的主要因素之一，利用CO₂驱替煤层CH₄，既可以增加CH₄产量，也可以降低空气中CO₂的含量，具有重要意义。本文以桑树坪煤样为主要研究对象，主要通过实验室实验、COMSOL模拟、现场工业性实验相结合的方式，分析研究CO₂驱替CH₄的影响因素及现场应用效果，主要研究成果如下：

实验数据的基础上结合langmuir拟合方程，拟合出了不同温度条件下，CO₂、CH₄的等温吸附曲线，并得出了吸附常数a、b值，通过对比发现，当温度升高时，无论CO₂还是CH₄的a、b值都呈现下降趋势，说明温度越高煤体对CO₂、CH₄的吸附能力越差，通过对比CO₂与CH₄在同一温度下的a值，煤体对CO₂的吸附能力远远大于CH₄。

利用自主搭建的实验平台，进行CO₂驱替CH₄物理相似模拟实验，开始阶段CH₄浓度基本不变，未发现CO₂气体；随着时间推移，CO₂浓度迅速增长，CH₄浓度下降；最终两种气体的浓度变化逐步放缓，趋于稳定，CH₄浓度趋近于0。

驱替实验过程中，随着注气压力的升高，CO₂突破煤体的时间逐步缩短，实验结束时间也随之缩短，CH₄的排出量和CO₂的吸附量增大，驱替置换比降低。随着环境温度升高，CO₂突破煤体时间延长，但是驱替完成时间无明显增长，CO₂的吸附量和CH₄的排出量下降，驱替置换比降低。通过对比不同注气温度的驱替结果，注气温度越高突破时间越短，实验结束越快。排出CH₄量与吸附CO₂量增加，驱替置换比降低。

在物理相似模拟实验的基础上开展数值模拟研究，通过分析数值模拟结果，发现注气压力越高气体突破时间与浓度变化时间越短，煤体渗透率越低气体突破时间越长浓度变化越缓慢，且距离进气口越近突破时间与浓度变化时间越短。

在桑树坪煤矿进行了现场实验，结果表明液态CO₂的相变驱替可明显提高煤层CH₄抽采效果，分析出随着驱替进行CO₂压力下降，导致后期CH₄抽采效果降低。

Gas accidents are one of the main threats to coal mine safety production, and the main component of gas is CH₄. CO₂ is one of the main factors contributing to the global greenhouse effect. The use of CO₂ to displace CH₄ from coal seams can increase the production of CH₄ and reduce the content of CO₂ in the air, which is of great significance. This paper takes Sangshuping coal sample as the main research object, then analyzes and studies the influencing factors of CO₂ displacing CH₄ and on-site application effects through a combination of laboratory experiments, COMSOL simulation, and on-site industrial experiments. The main research results are as follows:

On the basis of the experimental data combined with the langmuir fitting equation, the isotherm adsorption curves of CO₂ and CH₄ under different temperature conditions were fitted, and the adsorption constants a and b values were obtained. Through comparison, when the temperature rises, The a and b values of CO₂ and CH₄ both show a downward trend, and the higher the temperature, the worse the adsorption capacity of coal for CO₂ and CH₄. By comparing the a value of CO₂ and CH₄ at the same temperature, the adsorption capacity of coal for CO₂ is much larger than CH₄.

Using the self-built experimental platform, the physical simulation experiment of CO₂ displacing CH₄ was carried out. At the beginning, the CH₄ concentration was basically unchanged, and no CO₂ gas was found; as time passed, the CO₂ concentration increased rapidly, and the CH₄ concentration decreased; the final concentration of the two gases slowed down and stabilized gradually, and the CH₄ concentration approached zero.

During the displacement experiment, as the gas injection pressure increases, the time for CO₂ to break through the coal body is gradually shortened, and the end time of the experiment is also shortened. The discharge of CH₄ and the adsorption of CO₂ increase, and the displacement ratio is reduced. As the ambient temperature rises, the time for CO₂ to break through the coal body is prolonged, and the time for completion of the displacement does not increase significantly, and the amount of CO₂ adsorption and the amount of CH₄ discharged decreases, and the displacement ratio decreases. By comparing the displacement results of different gas injection temperatures, the higher the gas injection temperature, the shorter the breakthrough time and the faster the experimental process. The amount of discharged CH₄ and the amount of adsorbed CO₂ increase, and the displacement displacement ratio decreases.

Numerical simulation research is carried out on the basis of physical similarity simulation experiments. Through the analysis of the numerical simulation results, it is found that the higher the gas injection pressure is, the shorter the gas breakthrough time and concentration change time is, the lower the coal permeability is, the longer the gas breakthrough time is, the slower the concentration change is, and the closer it is to the air inlet, the shorter the breakthrough time and concentration change time are.

Industrial experiment was carried out in Sangshuping Coal Mine, and the results showed that the phase change displacement of liquid CO₂ can significantly improve the coal seam CH₄ extraction effect. It is analyzed that the CO₂ pressure drop as the displacement progresses, which leads to a decrease in the later CH₄ extraction effect.

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