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为了探索水力压裂条件下由软煤、软顶和软底构成的特殊地质体(简称“三软”煤层)裂缝的扩展规律,以及压裂后储层的裂隙分布特征,结合河南焦作煤层气田的注水压裂试验,基于PKN模型的裂缝宽度假设与裂缝流动的摩阻压降规律,着重考虑软煤裂隙中压裂液的滤失因素,构建了水力压裂条件下“三软”矿区碎裂煤的裂缝扩展模型与渗透率计算模型,并运用地震实测法和渗透率反演计算法分别进行了验证。研究结果表明,实际施工条件下试验区二_1煤层压裂后的裂缝几何特征大致相同,长度分布区间为81.85~139.23m,平均为100.41m;最大裂缝宽度区间为24.83~32.78mm,平均为27.32mm,裂缝长度与地震实测结果基本一致。应用裂缝渗透模型,进一步计算得到压裂后煤储层的渗透率一般在(9.21~86.61)×10~(-3)μm~2之间,平均为31.63×10~(-3)μm~2。与后期排采结果所得到的储层渗透率反演值相对比,二者基本吻合。由此可见,压裂改造后的煤储层的渗透率得到显著提高,裂缝扩展与裂缝渗透模型皆可应用于指导“三软”矿区的压裂抽采实践与产能预测。
In order to explore the propagation rules of fractures of special geological bodies (soft coal, soft roof and soft bottom) under hydraulic fracturing conditions and the fractures distribution characteristics of fractured reservoirs, Based on the PKN model’s crack width hypothesis and the frictional pressure drop law of fracture flow, this paper focuses on the filtration factors of fracturing fluid in soft coal fissure, “Fractured coal crack propagation model of coal and permeability calculation model, and the use of seismic measurements and permeability inversion calculation were validated. The results show that the geometrical characteristics of fractures of No.2 coal seam after the fracturing in the test area are almost the same under the actual construction conditions with the length distribution ranging from 81.85 to 139.23m with an average of 100.41m and the maximum fracture width ranging from 24.83 to 32.78mm 27.32mm, crack length and the measured results are basically the same. Applying the fracture infiltration model, the permeability of the coal reservoir after fracturing is calculated to be between (9.21 ~ 86.61) × 10 ~ (-3) μm ~ 2 and the average is 31.63 × 10 ~ (-3) μm ~ 2 . Compared with the retrieved value of reservoir permeability obtained from the result of late drainage, the two are in good agreement. It can be seen that the permeability of fractured coal reservoirs has been significantly improved. Both the crack propagation and fracture infiltration models can be used to guide the practice of fracturing and drainage and production capacity prediction in the ”Three Soft" mining area.