碎软低渗煤层在我国普遍发育，制约煤层气单井产气量提高和产业发展。间接压裂是通过在邻近层产生垂直裂缝沟通煤层进而实现煤层有效改造的一种压裂方式，可以有效应对钻井塌陷、煤粉产出、压裂液滤失和煤层厚度薄等不利因素。通过间接压裂物理模拟试验和扩展有限元数值模拟分析，揭示煤层顶板间接压裂裂缝扩展影响因素，明确裂缝扩展机制，以期为间接压裂技术提供指导。通过直接压裂煤层和不同起裂位置、垂向应力和施工排量影响下间接压裂试验表明，起裂压力高，更易产生长裂缝，且受原生裂缝影响程度减小；但起裂点距离煤层越远，起裂所需能量越大，高破裂压力会对煤层造成粉碎性破坏；大施工排量下，起裂压力对应升高，起裂时间变短，原生裂缝影响程度变小。考虑地应力、起裂位置、岩石力学和施工排量等参数的数值模拟结果显示，在模型参数设置条件下，最大水平主应力和垂向应力差在<4 MPa，煤层与顶板有效应力差>3 MPa、弹性模量差<15 GPa的地层和岩性组合适合间接压裂，起裂位置距离煤层最优距离为<6 m，施工排量需要根据力学性质、断裂能密度等参数确定最优范围。

Fractured soft and low permeability coalbed is commonly developed in China, which restricts the increase of single well gas production and industrial development of coalbed methane (CBM). Indirect fracturing is a kind of fracturing method to communicate with coal seams by creating vertical fractures in the neighboring layers and thus achieve effective coal seam transformation, which can solve disadvantages such as drilling collapse, coal dust production, fracturing fluid filtration loss and thin coal seam thickness. In this paper, physical simulation experiments and extended finite element numerical simulation analysis of indirect fracturing are used to reveal the factors influencing the fracture expansion of indirect fracturing in the coal seam roof and to clarify the fracture expansion mechanism in order to provide guidance for indirect fracturing technology. The indirect fracturing experiments under the influence of direct fracturing of coal seam and different fracture initiation location, vertical stress and construction displacement show that high fracture initiation pressure is more likely to produce long fractures, and the influence of primary fractures is significantly reduced; however, the farther the fracture initiation point is from the coal seam, the more energy is required for fracture initiation, and high fracture pressure will cause crushing damage to the coal seam; under large construction displacement, the fracture initiation pressure is correspondingly increased, the fracture initiation time becomes shorter, and the influence of primary fractures becomes smaller. The degree of impact of primary fracture becomes smaller. Under the condition of model parameter setting in this paper, the numerical simulation results considering the parameters of ground stress, fracture initiation location, rock mechanics and construction displacement show that the maximum horizontal principal stress and vertical stress difference is <4 MPa, the effective stress difference between coal seam and roof is >3 MPa, and the combination of coal and roof elastic modulus difference <15 GPa is suitable for indirect fracturing. The optimal distance of the fracturing location from the coal seam is <6 m. The optimal range of the construction displacement should be determined according to the mechanical properties, fracture energy density and other parameters.