脉冲波作用受载含瓦斯煤结构损伤及其致裂增渗机制研究

Permeability enhancement is crucial to gas high-efficiency extraction in low-permeability coal seam. The impulse wave produced by electric pulse technology has the characteristics of large instantaneous energy, strongly destructive force and repeatable action, which provides a new idea for enhancing the permeability of coal seam. However, the structural damage and the mechanism of cracking and permeability enhancement of the loaded coal containing gas under the action of impulse wave is not fully understood. Therefore, the method of combining experimental research, theoretical analysis and numerical simulation is applied in this project. And based on the three-axis servo control seepage test system of coal cracked by impulse wave and other equipment, the impact dynamic characteristic as well as the structural damage and permeability evolution of coal body under the coupling action of dynamic and static loads of in-situ stress, gas pressure and impulse wave are studied. The propagation mechanism and its main controlling factors of impulse wave in coal containing gas is explored, and combining with microcosmic-microscopic view analysis means, the spatial distribution characteristics of pore-fissure of coal and its effective range under the action of different combinations of impulse wave parameter are illustrated. Based on the analysis of the seepage characteristics of the loaded coal containing gas cracked by impulse wave, the coupling mechanism of structural damage and gas seepage in coal containing gas is revealed, and a coupling model of structural damage-gas seepage in coal containing gas cracked by impulse wave is established. Finally, an impulse wave parameter optimization method used to expand the area where the permeability increases effectively is proposed. The research results are of great theoretical significance to the formation of the theory and method of impulse wave cracking and permeability enhancement based on the principle of electric pulse as well as its application.

增透是低渗煤层瓦斯高效抽采的关键，以电脉冲技术为基础的脉冲波具有瞬时能量大、冲击破坏力强和可重复作用的特点，为煤层增透提供了新思路，但对其作用受载含瓦斯煤结构损伤与致裂增渗机制认识不充分。为此，本项目采用试验研究、理论分析和数值模拟相结合的方法，基于脉冲波致裂煤体三轴伺服控制渗流试验系统等设备，开展地应力、瓦斯压力与脉冲波动静荷载耦合作用下煤体冲击动力特性及其结构损伤与渗透性演化规律研究，探究脉冲波作用含瓦斯煤的传播机制及其主控因素，结合微细观分析方法阐明不同脉冲波参量组合条件下煤体孔隙-裂隙空间分布特征及有效作用范围；基于脉冲波致裂受载含瓦斯煤渗流特性分析，揭示脉冲波作用含瓦斯煤结构损伤与其渗流耦合作用机理，建立脉冲波致裂含瓦斯煤结构损伤-瓦斯渗流耦合模型，提出扩大有效增渗范围的脉冲波参量优化方法。研究成果对形成基于电脉冲原理的脉冲波致裂增渗理论与方法及其推广应用具有重要的理论意义。

随着我国煤炭开采深度不断增加，煤层赋存环境变得更加复杂，为了实现低渗煤层瓦斯高效抽采及瓦斯灾害防治，有必要探索适合我国深部煤层赋存状况的安全高效增渗新技术。脉冲波具有瞬时能量大、冲击破坏力强、可重复作业等优点，为深部低渗煤层致裂增渗提供了一个新途径，但是脉冲波作用煤体致裂增渗基础理论研究滞后于工程实践，导致现场应用中缺乏有效的理论指导。为此，本项目结合理论分析、物理试验和数值模拟等方法开展了研究，并取得了以下主要研究成果：建立了脉冲波致裂受载煤岩增渗实验系统，可开展更符合煤层实际赋存环境的脉冲波作用受载煤体结构损伤特征及其渗流演化规律研究；研究了不同条件下脉冲波作用煤体的冲击动力演化特征，探明了脉冲波作用煤体的不同位置压力随着时间都经历先上升后下降的过程，脉冲波作用煤体的峰值压力随着传播距离的增加会不断衰减，当脉冲波作用煤体的压力小于煤体力学强度时，煤体不再发生损伤破坏；开展了不同条件下脉冲波作用煤体的宏细观结构损伤演化规律研究，明确了脉冲波能够有效改善煤体内部孔隙结构，脉冲波作用后煤体内部微孔、中孔和大孔的孔隙度均有明显提高，并且脉冲波作用煤体过程中会形成多条以张拉破坏为主要形式的贯穿裂缝，能够有利于改善煤体的渗透性；开展了脉冲波作用受载煤体的渗透性演化规律研究，发现在相同的应力加载和进气压力条件下，脉冲波作用后煤体的渗透率明显大于原煤，基于试验结果及理论分析揭示了脉冲波作用受载煤体的致裂增渗机制。研究成果能够为脉冲波在深部低渗透煤层致裂增渗现场应用及工艺参数制定和优化提供理论依据。