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煤层气井地面压裂和井下长钻孔联合抽采技术研究

Study on combined extraction technology of underground longborehole and CBM ground-well fracturing

  • 摘要: 晋城矿区煤层含气量高、渗透率低,单一的地面或井下抽采效果不理想,为使煤矿安全开采,须结合井下长钻孔部署的局部范围卸压增渗的瓦斯预抽技术,使煤层渗透性得到成倍提高。采用微地震法及电位法等人工裂缝监测技术,对试验井压裂的裂缝形态和有效半径进行了评价,以试验区百米钻孔瓦斯流量、瓦斯浓度等相关参数作为考察对象,分析研究了地面压裂与井下长钻孔施工的时空衔接关系。研究结果表明:试验区地面井压裂影响范围呈椭圆区间,长半轴为120~150m,短半轴为50~80m,裂缝形态以水平裂缝为主;压裂影响区内百米钻孔瓦斯流量是压裂区外的1.33~17.50倍,瓦斯体积分数平均提高了35%;地面压裂与井下抽采衔接越紧密抽采效果越好,地面压裂施工后优先施工稳定性较好的煤层顶板钻孔,待压裂裂缝与煤体达到新的动态平衡后再施工顺煤层钻孔;综合考虑抽采效果及井下安全,压裂井井底与已掘巷道、已施工钻孔距离150~200m为宜。

     

    Abstract: Due to the high gas content and low permeability of coal seam in Jincheng mining area,the single ground or underground gas drainage effect is not ideal.In order to make the coal mining safe,a continuous exploration that combined ground fracturing with underground long holes gas drainage to increase permeability become more and more important.The fracture morphology and effective radius of the test well fracturing were evaluated by artificial seismic monitoring techniques such as microseismic method and potential method.The parameters such as gas flow and gas concentration in the test area were investigated,and the temporal-spatial relationship between ground fracturing and underground gas extraction were analyzed.The results show that the fracturing range of the ground well in the test area was elliptical,with the long semi-axis being 120~150 m and the short semi-axis being 50~80 m,and most of the crack form was horizontal.The gas flow rateof 100-meter borehole in the affected zone is 1.33~17.50 times outside the fracturing zone,and the gas concentration increased by an ave rage of 35%.The closer the ground fracturing is combined with the downhole drainage,the better the drainage effect is.The coal seam with better construction stability after ground fracturing construction is preferred.After the fracturing crack and the coal body reach a new dynamic balance,and then drilling the coal seam.After comprehensively considering the drainage effect and the safety of the well,that the distance between the bottom of the fractured well and the excavated roadway and the constructed drilling hole distance of 150~200 m is suitable.

     

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