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淮南矿区煤层顶板分段压裂水平井抽采技术及效果研究

Study on technology and effect of gas extraction in horizontal well with segmental hydraulic fracture in roof of coal seam in Huainan mining area

  • 摘要: 淮南矿区为典型高瓦斯矿区,煤层碎软、渗透率低、瓦斯含量偏高、抽采难度大,为探讨地面煤层气顶板分段压裂水平井在矿区的技术可行性与瓦斯治理效果,在分析矿区主要煤层13-1煤储层特征基础上,采用应力解除法进行了煤层三向地应力测试,结果显示三向应力场类型主要为σh,max >σv >σh,min,具有实施顶板分段压裂水平井技术的充分条件;利用MFrac Suite软件分别模拟了水平段距离煤层1、3、5 m时的压裂缝参数,压裂缝半长最大107.33 m、最小89.47 m,具有理想的压裂效果,说明顶板分段压裂水平井在淮南矿区具有比较好的地质适应性与可行性。以潘一煤矿13-1煤层“L”型顶板分段压裂水平井CBM01井为研究对象,采用井下钻孔检测与数值模拟等手段综合分析了瓦斯治理效果,结果显示CBM01井抽采415 d即显著降低了煤层瓦斯压力与瓦斯含量,距离水平井50、65 m处瓦斯压力由6.4 MPa分别降至2.6、2.7 MPa,降低幅度均超过55 %,水平段两侧各15~20 m范围内瓦斯含量由13.5 m3/t降至最大9.11 m3/t、最小6.92 m3/t,平均7.92 m3/t,约10 m范围均降至8 m3/t以下。最后,采用数值模拟方法预测了CBM01井抽采10 a的产气效果及瓦斯治理效果,气井抽采10 a累计产气约272.08×104 m3,水平段倾向单侧约150 m范围内气含量均降至8 m3/t以下、压力均降至3 MPa以下。综合研究结果表明,煤层顶板分段压裂水平井技术在淮南矿区瓦斯治理方面均具有较大的优势和应用效果。

     

    Abstract: Huainan mining area is a typical high-gas area, with broken soft coal seam, low permeability, high gas content, and difficulty in extraction. In order to probe into the technical feasibility and gas control effect of the horizontal well for segmental hydraulic fracture in roof of coal seam in mining area, a three-dimensional in-situ stress test of coal seam was carried out using the stress relief method based on the analysis of the characteristics of the 13-1 coal reservoir, which was the main coal seam in the mining area. The results shown that, the three-dimensional stress field was mainlyσh,max >σv >σh,min, which had sufficient conditions for the implementation of horizontal well with segmental hydraulic fracture in roof of coal seam. MFrac Suite software was used to simulate the fracture parameters of horizontal section at 1, 3 and 5 m from the coal seam. The maximum half-length of the fracture was 107.33 m and the minimum was 89.47 m, which was ideal for fracturing, indicating that the horizontal well with segmental hydraulic fracture had better geological adaptability and feasibility in Huainan mining area. Taking the CBM01 well, a horizontal well with L-type roof segmental fracturing in the 13-1 coal seam of Panyi coal mine, as the research object, the effect of gas control and management was comprehensively analyzed by means of borehole detection and numerical simulation. The results shown that, CBM01 well significantly reduced the gas pressure and gas content of coal seam after 415 d of extraction. The gas pressure at 50 and 65 m from the horizontal well decreased from 6.4 MPa to 2.6 and 2.7 MPa, respectively, by more than 55%. The gas content decreased from 13.5 m3/t to a maximum of 9.11 m3/t, a minimum of 6.92 m3/t, an average of 7.92 m3/t in an area of about 15-20 m on each side of the horizontal section, and decreased to less than 8 m3/t within about 10 m. Finally, a numerical simulation method was used to predict the gas production effect of CBM 01 well extracting for 10 a and the effect with gas control. The cumulative gas production of gas well was about 272.08×104 m3 in 10 a, and the gas content in the range of about 150 m on one side of the horizontal section was reduced to less than 8 m3/t, and the pressure was reduced to less than 3 MPa. Comprehensive research results shown that the horizontal well technology of segmental hydraulic fracturing in roof of coal seam had greater advantage and application effect in gas control and management in Huainan mining area.

     

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