高压气体冲击作用下含瓦斯煤体的裂纹扩展及扰动规律研究

With the increasing of coal-mining depth, characteristics of micropores, low permeability and high absorbability of gas-filled coal become more obvious, which lead to the increasing difficulty and poor effect for gas extraction. As a blasting technology of high-pressure gas with good cracking effect and high security, the cracking technology of CO2 has been introduced into the field of gas extraction and coal-seam penetration. However, the research on the cracking mechanism of high-pressure gas stays at the initial stage of development, and the further application and promotion of the cracking technology of high-pressure gas are limited. Firstly, the initial stress field is to be solved and the initial damage state is to be described for fractured coal in crustal stress. Then, with the theory of damage mechanics, fracture mechanics and fluid mechanics and the results of triaxial compression tests, blasting tests of high-pressure gas and numerical simulation tests, the fluid-driving model, crack propagation condition, damage evolution equation and failure criterion of gas-filled coal under of action of crustal stress, seam gas pressure and high -pressure gas will be established. Cracking mechanism of coal in multiple stresses of crustal stress, seam gas pressure and high -pressure gas will be studied. Furthermore, mechanism of propagation for macroscopic crack in coal near the borehole and mechanism of disturbance of stress field for microscopic crack in coal away from the borehole will be revealed. The subject can provide powerful theoretical foundation for further promoting the application of the cracking technology of high-pressure gas and improving the effect of gas extraction.

随着煤矿开采深度的持续增大，含瓦斯煤层微孔隙、低渗透性和高吸附的赋存特征愈发明显，瓦斯抽采难度加大，抽采效果不理想。作为一项致裂效果好、安全性高的高压气体爆破技术，CO2致裂技术被引入至瓦斯抽采和煤层增透领域。但高压气体致裂机理研究仍停留在发展的初期阶段，导致高压气体致裂技术的深入应用和进一步推广受到限制。拟运用损伤力学、断裂力学和流体力学等理论，综合三轴压缩试验、气爆试验及数值模拟试验结果，在对地应力作用下裂隙煤体初始应力场求解和初始损伤描述的基础上，建立含瓦斯煤体在地应力、瓦斯压力和高压气体共同作用下的流体驱动模型、裂纹扩展准则、损伤演化方程和破坏准则，研究地应力、瓦斯压力和高压气体等多重应力作用下的煤体致裂机理，从而揭示高压气体冲击作用下钻孔近区煤体宏观裂纹的扩展机理和钻孔远区煤体细观裂纹的应力场扰动机理。为进一步推广高压气体致裂技术和提高瓦斯抽采效果提供有力的理论依据。

高压气体冲击作为一种现代化无水致裂技术在低渗透性非常规气体储层增透领域被广泛应用。然而，高压气体冲击煤体致裂机理研究的理论还不够完善，现场实际应用效果还不够理想。因此，围绕高压气体冲击煤岩体诱发的裂纹扩展及扰动规律两个科学问题，综合采用文献调研、理论分析、室内试验和数值仿真模拟等方法，系统开展了高压气体冲击作用下含瓦斯煤体的裂纹扩展及扰动规律研究，对提高瓦斯高效抽采具有科学意义。.确定了高压气体单次和多次冲击下煤岩体启裂判据条件，构建了高压气体冲击下含瓦斯煤的孔隙率、损伤和有效应力的动态演化本构方程。基于工程实际调研和煤体力学性质，确定了五类煤体的相似材料及配合比；自主研发了一套大尺寸试件双向加压装置及高压气体冲击系统，实现了双向围压加载条件下的高压气体冲击模拟环境。基于室内高压气体单/多次冲击煤岩体的模拟试验，揭示了高压气体冲击炮孔孔壁压力特征，探究高压气体冲击作用下煤体内部应力场的分布、裂隙发育与围压之间的关系，分析了冲击次数对试件内部孔-裂隙结构演化规律，探讨冲击次数对煤岩体介质动态演化过程的影响，揭示高压气体冲击下煤岩体介质的断裂及累积损伤机理。采用Ansys建立了数值计算模型，探究围压压力对裂纹扩展行径的影响。构建了高压气体冲击前后试件不同区域内的三维可视化模型，分析高压气体冲击对煤岩体介质不同区域内孔裂隙结构演化特性和规律，基于孔隙率变化初步探索确定了高压气体冲击下的扰动范围。基于天然煤体高压气体冲击试验，建立了冲击前后的天然煤体的微观尺度可视化模型，实现了微观尺度CH4渗流可视化模拟，探究了气体在微观多孔隙介质结构中的运移扩散过程及分布规律。