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通过定义煤层气的压降波及效率、解吸效率与游离气滞留率,提出了一种煤层气采收率的分析计算公式.在此基础上研究了开采过程中煤层气的逸散过程,认为煤层气的逸散是由逸散速度比与逸散距离比共同决定,若煤层气逸散距离比大于逸散速度比的最大值,则可以认为煤层气无法发生逸散.同时,模拟计算了不同地质及工程因素对煤层气的采收率、压降波及效率、解吸效率和煤层气逸散比例的影响.研究结果表明:开采过程中煤层气的逸散可以损失10%左右的储量,距井眼70m以外的煤层气均会逸散至顶板.中等含气煤层的逸散量相较于高含气和低含气煤层的逸散量多.废弃压力对逸散的影响并不单调,可以优化废弃压力使逸散量达到最小.合适的井网以及负压采气措施可以有效降低逸散量,提高煤层气的采收率.
By defining the pressure drop efficiency and desorption efficiency of CBM and the retention rate of free gas, a formula for calculating and calculating the CBM recovery rate is proposed. Based on this, the process of coalbed methane release during the mining process is studied, Gas emission is determined by the ratio of escape velocity to escape distance. If the ratio of escape velocity of coal-bed methane is greater than the maximum of escape velocity ratio, it can be assumed that coal-bed methane can not escape. Simultaneously, Geological and engineering factors on CBM recovery efficiency, pressure drop efficiency, desorption efficiency and the proportion of coal-bed methane emission.The results show that: the escape of coal bed methane can lose about 10% of the reserves during the mining process, The CBM will escape to the top of the roof beyond 70m.The amount of fugacity of medium gas coal is higher than that of high gas and low gas coal.The impact of waste pressure on fugitive emissions is not monotonous, Optimize the waste pressure to minimize the fugacity.Appropriate well pattern and negative pressure gas recovery measures can effectively reduce the amount of fugacity and improve the recovery rate of CBM.