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阳泉−晋城矿区关闭煤矿煤层气资源特征及抽采模式

Characteristics and drainage modes of coalbed methane resources in closed coal mines in Yangquan and Jincheng Mining Areas

  • 摘要: 受资源枯竭、淘汰落后、过剩产能等因素影响,山西省关闭煤矿数量逐年增多,关闭/废弃煤矿煤层气资源评价和开发逐渐受到重视。笔者以阳泉−晋城矿区关闭煤矿为研究对象,通过资料整理、实验测试、数值模拟等手段,探究了关闭煤矿煤层气资源特征,预测了煤层气资源量,总结了抽采模式。研究表明,阳泉−晋城矿区2009年兼并重组前和兼并重组中关闭煤矿共153座,基本为低瓦斯煤矿。2016―2020年去产能关闭37座煤矿,阳泉矿区分布较为集中,以高瓦斯矿为主;晋城矿区分布相对零散,以低瓦斯矿井为主。关闭煤矿煤层气资源由采空区煤层气资源与原位煤层气资源组成。采空区煤层气以游离态为主赋存于采空区孔隙−裂隙中,厚煤层采空区垮落带与裂隙带孔隙体积之和与工作面体积的比值I介于0.53~0.73,而中厚煤层采空区I值通常大于0.90。原位煤层气主要以吸附态赋存于煤基质孔隙中,15号煤孔隙度介于3.69%~5.45%,微孔比表面积介于97.58~120.76 m2/g,微孔体积介于0.017~0.022 cm3/g,微孔最为发育。煤层埋深和局部构造控制原位煤层含气性,而甲烷浓度作为采空区含气性的重要指标,受控于煤层、储气空间结构及封闭条件。根据资源与关闭煤矿特征将关闭煤矿煤层气资源分为3类:低瓦斯关闭煤矿采空区煤层气资源、高瓦斯关闭煤矿采空区煤层气资源和高瓦斯关闭煤矿原位煤层气资源。构建了关闭煤矿采空区煤层气资源量预测数学模型,预测了采空区煤层气资源量;采用体积法预测了原位煤层气资源量。在资源预测范围内,阳泉−晋城矿区关闭煤矿采空区煤层气资源量合计46074.01×104 m3,原位煤层气资源量达146388.12×104 m3,其中,阳泉三矿的资源量最大。此外,总结了4种关闭煤矿煤层气抽采模式,分别为地面直井抽采、L型井抽采、采空区煤层气与水平邻近原位煤层气合采及过采空区下部煤层气抽采,并针对各关闭煤矿提出了利用方向。

     

    Abstract: Affected by factors such as coal resources exhaustion, elimination of outdated and excess capacity, the number of closed coal mines in Shanxi Province has increased year by year, and the evaluation and exploration of closed or abandoned coal mine coalbed methane resources has gradually received attention. In this study, the closed coal mines in Yangquan and Jincheng Mining Areasare taken as the research object. Through data collation, experimental test, numerical simulation and other means, the characteristics of coalbed methane resources in closed coal mines are explored, the amount of coalbed methane resources is predicted, and the drainage modesare summarized. The research shows that 153 coal mines in Yangquan and Jincheng Mining Areas were closed before and during the merger and reorganization in 2009, whose were dominated by low-gas coal mine. From 2016 to 2020, 37 coal mines were closed due to capacity elimination. The closed coal mines in Yangquan Mining Area are concentrated and mainly high-gas mines. The distribution of closed coal mines in Jincheng Mining Area is relatively scattered with mainly low-gas mines. The coalbed methane resources in closed coal mine are composed of gob coalbed methane resources and in-situ coalbed methane resources. Gob coalbed methane mainly exists in the pore-fracture of gob as the free state. The ratio I of the sum of pore-fracture volume in the caving zone and fracture zone of gob to the working face volume in thick coal seam ranges from 0.53 to 0.73, while that in medium-thick coal seam is generally greater than 0.90. The in-situ coalbed methane is mainly adsorbed in the pores of coal matrix. The porosity of No.15 coal seam is between 3.69%~5.45%, the specific surface area of micropores is 97.58~120.76 m2/g, and the volume of micropores ranges from 0.017~0.022 cm3/g, indicating that micropores are the most developed. The depth of coal seam and the local geological structure control the gas content of the in-situ coal seam, while as an important index of the gas content of the gob, methane concentration is controlled by the coal seam, gas storage space structure and sealing conditions. According to the characteristics of resources and closed coal mines, the closed coal mine coalbed methane resources are divided into three categories: gob coalbed methane resources in low-gas closed coal mine, gob coalbed methane resources in high-gas closed coal mine, and in-situ coalbed methane resources in high-gas closed coal mine.The amount of gob coalbed methane resources in closed coal mines was predicted by constructing a new mathematical model. Besides, the amount of the in-situ coalbed methane resourceswas predicted by the volume method. Within the range of resourceprediction, the total amount of gob coalbed methane resources is 46074.01×104 m3, and the amount of in-situ coalbed methane resources can reach 146388.12×104 m3, among which Yangquan No.3 Mine has the largest amount. In addition, four coalbed methane drainage modes in closed coal mines are summarized, including surface vertical well drainage, L-shaped well drainage, co-drainage of gob and horizontal adjacent in-situ coalbed methane resources, and coalbed methane drainage under gob. Furthermore, the utilization direction is proposed for each closed coal mine.

     

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