低煤阶煤层含气量特征及瓦斯涌出机制探讨

煤层含气量是表征煤层气储层特征的关键参数之一。为了准确获取低煤阶煤层含气量，以彬长矿区大佛寺煤矿为例，根据Langmuir方程和排采过程中实测的临界解吸压力计算了4号煤层含气量。根据计算结果，4号煤层含气量为2.30~3.62 m^3/t，平均为2..87 m^3/t，是煤层含气量测试结果的0.88~1.93倍，符合低阶煤的特征，最为接近4号煤层原始含气量。并根据矿山岩层移动理论和渗流理论探讨了4号煤层含气量低而煤矿生产过程中瓦斯涌出量大的原因。分析认为，煤层在开采过程中，随着顶、底板岩层变形、垮落和移动，应力释放使煤体产生大量的新生裂隙，改变了煤体结构特征，促使煤层渗透性发生了根本性的改变，形成卸压增透和增流效应，造成大佛寺煤矿瓦斯涌出量急剧增大。 

GAS CONTENT AND GAS GUSH MECHANISM OF LOW-RANK COAL SEAM

Coal seam gas content is one of key indicators in marking CBM reservoir features. To precisely obtain gas content of low-rank coal seam, this paper, based on a case study on Dafosi coal mine, Binchang district, uses Langmuir formula to calculate the gas content of No.4 coal seam through measuring the critical desorption pressure during extraction, with the results showing gas content 2.30-3.62 m^3/t, 2.87 m^3/t on average, 0.8 to 1.93 times test gas content, corresponding to the feature of low-rank coal, very close to the original gas content of No.4 coal seam. This paper also discusses the reason of gas gush during mining No.4 coal seam according to rock movement theory and flow theory. Release of stress produces new fissures as top and bottom transform, collapse and move in the process of coal mining, changing coal seam structures and permeability, leading to pressure-relief-permeability-rising and flow-increasing effects, which makes gas gush of Dafosi coal mine.