Influence of fracturing pressure of vertical well to CBM capacity in Jiulishan coal mine
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摘要: 为了总结豫北焦作矿区九里山煤矿煤层气井压裂抽采试验的成功经验与失败教训，基于弹性平面应变理论和数值模拟方法，讨论了煤岩体压裂缝的形成与发展机理，并推导了“三软”煤层压裂抽采井在不同地质条件下的起裂压力计算公式。通过对比计算结果与实际抽放试验资料，认识到在张性断裂构造发育的大水矿区，过大的压裂措施使煤层气井筒附近煤储层隔水底板受到较为严重的损伤，压裂缝转向底板太原组L7-8岩溶含水层, 导致大量地下水涌入地面采井。从产能效果看，强烈的地下水径流作用，使原先游离于储层空隙中的煤层气逸散殆尽，孔隙水压也使得大量吸附于裂隙中的煤层气难以解析，因而无法形成长期稳定的单井规模产量。Abstract: Based on the elastic plane strain theory, this article deduces the crack pressure calculation formula of fracturing extraction wells under different geological constructions in order to summarize the successes and the failures of the fracturing extraction experiment in the Jiulishan coal mine of the Jiaozuo coal field. By comparing the computation results with the actual drainage test data, it is found that in the tensile fracture development areas, the overlarge fracture measures will do great harm to the impermeable bases of coal reservoirs near the coal bed gas wells, and the fracturing fractures spread to the L7-8 karst aquifer of the Taiyuan Group, resulting in a large number of underground water into the surface wells. The fierce river course of groundwater makes almost all the coal bed gas escape from the interspaces of the reservoir stratums where it stays. Additional water pressure makes it difficult for much coal bed gas absorbed in fissures to escape, so it cannot form a long-term stable single well scale output.
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Key words:
- Jiulishan coal mine /
- “three soft” coal seam /
- CBM vertical well /
- fracturing pressure
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