煤层顶板水平井定向射孔压裂是碎软煤层煤层气（瓦斯）高效抽采的重要技术之一，掌握裂缝起裂特征能够为压裂方案设计提供理论支撑。考虑煤层及其顶板层理发育情况，结合水平井井眼距煤层距离，构建压裂地质工程模型；推导不同起裂模式水压判别式并进行验证；分析不同起裂模式的起裂压力变化规律，预测不同工况条件下裂缝的初始形态。结果表明：顶板水平井定向射孔压裂存在4种工况条件；煤层和结构弱面（层理、界面）起裂所需水压小于顶板，顶板水平井定向射孔压裂首次起裂点位于射孔孔眼根部，易在结构面及煤层位置再次破裂；地应力场条件影响着不同位置的起裂顺序。顶板中层理的发育增加了裂缝扩展过程中的起裂点，影响裂缝扩展路径，使顶板中的裂缝形态更为复杂；大部分条件下，射孔孔眼进入煤层，更有利于煤层起裂。相关研究丰富了顶板压裂理论，有助于煤层顶板水平井技术的推广。

Directional perforation fracturing of horizontal wells in coal seam roof is one of the important technologies for efficient extraction of coalbed methane (gas) in broken soft coal seams. Mastering the characteristics of crack initiation can provide theoretical support for fracturing scheme design. Considering the development of coal seam and its roof bedding, combined with the distance between the horizontal well and the coal seam, the fracturing geological engineering model was constructed. The water pressure discriminant of different initiation modes was deduced and verified. The variation law of crack initiation pressure under different crack initiation modes was analyzed, and the initial shape of cracks under different working conditions was predicted. The results show that there are four working conditions for directional perforation fracturing of roof horizontal wells. The water pressure required for crack initiation of coal seam and structural weak surface (bedding and interface) is less than that of roof. The first crack initiation point of directional perforation fracturing of roof horizontal well is located at the root of perforation hole, which is easy to break again at the position of structural surface and coal seam. The in-situ stress field conditions affect the crack initiation sequence at different positions. The development of the bedding in the roof increases the crack initiation point in the process of crack propagation, affects the crack propagation path, and makes the crack morphology in the roof more complex. Under most conditions, the perforation hole enters the coal seam, which is more conducive to coal seam cracking. The related research enriches the theory of roof fracturing and contributes to the promotion of horizontal well technology in coal seam roof.