Low permeability is the main constraint on the high-efficiency coalbed methane recovery in deep coal seams. Hydraulic slotting has been proved to be a favorable method to stimulate low-permeability coal seams. In this paper, the coal samples with various slot inclination angles and borehole-slot ratios were used to investigate the weakening effect of slot inclination angle and borehole-slot ratio on the mechanical property of the pre-cracked coal. Besides, the crack patterns of the slotted coal specimens were identified to reveal the slot weakening mechanism. It is revealed that the variations in compression strength, elastic modulus and Poisson’s ratio with the slot inclination angle generally conform to a Boltzmann function, logistic function and quadratic function, respectively. With the increase in the borehole-slot ratio, the curve clusters of compression strength and elastic modulus show the horizontal “V” with left opening, and the curve clusters of Poisson’s ratio show the trend of rapid increase after slow increase. Compared with elastic modulus, the slot weakening degrees of compression strength and Poisson’s ratio are more significant. Moreover, the tensile and shear cracks mainly appear in the coal samples with small and large slot inclination angles, respectively, which verify the fact that the slot weakening effect on mechanical property of the slotted coal samples with small slot inclination angles is more significant. The research achievements are attributed to the improvement in the efficiency of the hydraulic slotting-based enhanced coalbed methane recovery.

中文翻译：

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缝隙倾角和孔缝比对预裂煤力学性能的影响：水力缝隙对ECBM回收的意义

低渗透率是深部煤层高效采煤的甲烷采收的主要制约因素。事实证明，水力开挖是刺激低渗煤层的有利方法。本文采用不同缝隙倾角和井孔比的煤样，研究了缝隙倾角和井孔比对预裂化煤力学性能的影响。此外，还确定了开槽煤样品的裂纹模式，以揭示开槽的弱化机理。结果表明，压缩强度，弹性模量和泊松比随缝隙倾斜角的变化通常分别符合玻尔兹曼函数，对数函数和二次函数。随着井孔比的增加，压缩强度和弹性模量的曲线簇显示水平“ V”向左开，泊松比的曲线簇显示缓慢增加后迅速增加的趋势。与弹性模量相比，缝隙的抗压强度和泊松比的减弱程度更为显着。此外，拉伸裂纹和剪切裂纹主要出现在缝隙倾角较小和较大的煤样中，这证明了缝隙减弱对缝隙倾角较小的缝隙煤样的力学性能的影响更为显着。研究成果归功于基于水力开槽的强化煤层气采收率的提高。泊松比的曲线簇呈缓慢增加后缓慢增加的趋势。与弹性模量相比，缝隙的抗压强度和泊松比的减弱程度更为显着。此外，拉伸裂纹和剪切裂纹主要出现在缝隙倾角较小和较大的煤样中，这证明了缝隙减弱对缝隙倾角较小的缝隙煤样的力学性能的影响更为显着。研究成果归功于基于水力开槽的强化煤层气采收率的提高。泊松比的曲线簇呈缓慢增加后缓慢增加的趋势。与弹性模量相比，缝隙的抗压强度和泊松比的减弱程度更为显着。此外，拉伸裂纹和剪切裂纹主要出现在缝隙倾角较小和较大的煤样中，这证明了缝隙减弱对缝隙倾角较小的缝隙煤样的力学性能的影响更为显着。研究成果归功于基于水力开槽的强化煤层气采收率的提高。缝隙抗压强度的弱化程度和泊松比更为显着。此外，拉伸裂纹和剪切裂纹主要出现在缝隙倾角较小和较大的煤样中，这证明了缝隙减弱对缝隙倾角较小的缝隙煤样的力学性能的影响更为显着。研究成果归功于基于水力开槽的强化煤层气采收率的提高。缝隙抗压强度的弱化程度和泊松比更为显着。此外，拉伸裂纹和剪切裂纹主要出现在缝隙倾角较小和较大的煤样中，这证明了缝隙减弱对缝隙倾角较小的缝隙煤样的力学性能的影响更为显着。研究成果归功于基于水力开槽的强化煤层气采收率的提高。