Abstract Tree-type hydraulic fracturing is a new technology that can uniformly increase the permeability of coal seams. The existing initiation pressure prediction models do not fully consider the characteristics of coal seams and are not suitable for tree-type hydraulic fracturing. In this paper, an initiation pressure prediction model considering coal seam joints and gas pressure is established. In this model, the fracture failure modes of coal seam fracturing are calculated separately to accurately predict the failure mode and initiation pressure. Statistics and reasons are obtained for the fracture initiation position and the failure mode of tree-type hydraulic fracturing under different conditions. The fracture failure modes of a gas-bearing coal seam are mainly tensile failure and coal matrix failure, and tensile failure along bedding planes is the most common. The effects of 7 factors, including coal seam geological parameters, fracturing hole arrangement parameters and tree-type branch borehole arrangement parameters, on the fracture initiation pressure of tree-type hydraulic fracturing are analyzed. Among them, the angle between the tree-type branch borehole and the maximum principal ground stress direction is the only major influential factor that can be artificially controlled. The fracture initiation pressure is lowest when the tree-type branch borehole lies along the direction of the minimum principal ground stress. The results of a field experiment show that the theoretical initiation pressure and the actual initiation pressure are within 6.3%. In addition, compared with traditional fracturing technology, tree-type hydraulic fracturing technology can reduce the initiation pressure. The proposed model can provide a reference for field applications of tree-type hydraulic fracturing technology.

中文翻译：

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含气煤层树型水力压裂的起裂压力及破坏模式

摘要 树型水力压裂是一种能​​均匀提高煤层渗透率的新技术。现有的起裂压力预测模型没有充分考虑煤层特征，不适合树型水力压裂。本文建立了考虑煤层节理和瓦斯压力的起裂压力预测模型。该模型分别计算煤层压裂的破裂破坏模式，准确预测破坏模式和起裂压力。对不同条件下树型水力压裂的起裂位置和破坏模式进行了统计和原因分析。含气煤层的断裂破坏模式主要是拉伸破坏和煤基破坏，沿层理平面的拉伸破坏是最常见的。分析了煤层地质参数、压裂孔布置参数和树型分支井布置参数7个因素对树型水力压裂起裂压力的影响。其中，树状分支钻孔与最大主地应力方向的夹角是唯一可以人为控制的主要影响因素。树型分支钻孔沿最小主地应力方向时，起裂压力最低。现场试验结果表明，理论起爆压力与实际起爆压力在6.3%以内。此外，与传统压裂技术相比，树型水力压裂技术可降低起裂压力。该模型可为树型水力压裂技术的现场应用提供参考。