深部多尺度裂隙煤体瓦斯多机制流动理论研究

It is meaningful to study the multi-mechanism flow theory of deep multi-scale fracture coal for efficiently exploiting coalbed methane, ensuring the mining safety of the deep coal seams, adjusting the structure of energy consumption and solving the social problem of smog in our country. In order to solve the key science problems of methane drainage in deep seams, the distribution of pore and crack in coal at different scales is observed using by the micro, meso and macro experimental testing means. And meanwhile, the internal pore and crack structure of coal is finely characterized with the fractal theory. And then, the tests of methane film permeation and methane elution at different scales are carried out in laboratory. Moreover, the methane flow law of multi mechanisms and multi scale flow behavior are analyzed based on the fact of the coexistence of multi flow mechanisms and the crossing scale migration during the process of coalbed methane drainage. In addition, the methane flow equation of multi mechanism and the HTM coupling model of methane fractal-statistical multi mechanism flow are built up, which can used to uncover the methane flow law of multi mechanisms in deep fractured coal. Furthermore, the multi-scale methane drainage model of deep coal is set up to form the multi-scale numerical simulation method for methane flow law in deep coal seams. Finally, the measures suggest the improving coal permeability for coalbed methane drainage is proposed on the basis of the essence and effectiveness the conventional technology measures of improving coal permeability in deep coal seam mining practice. The research results of this project can be a good support for coalbed methane drainage and safe production of deep coal mining in our country.

研究深部多尺度裂隙煤体瓦斯多机制流动理论对我国高效开发煤层瓦斯、确保深部煤层安全开采、调整能源消费结构、解决当前“雾霾”等社会难题具有重要意义。为解决深部煤层瓦斯有效抽采关键科学问题，本项目以深部多尺度裂隙煤体为研究对象，利用微、细、宏观测试手段，观测不同尺度条件下煤体孔隙裂隙发育和分布情况，对煤体孔缝结构特征进行精细表征；开展瓦斯气体薄膜透过性测试和多尺度煤体瓦斯放散试验，结合煤层瓦斯抽采过程中多种流动机制共存和跨尺度运移的客观事实，分析瓦斯多机制流动规律和多尺度流动行为，建立煤体孔隙瓦斯多机制流动方程和深部煤体瓦斯分形统计多机制流动HTM耦合模型，揭示深部裂隙煤体瓦斯多机制流动规律；构建深部裂隙煤体多尺度瓦斯抽采模型，形成多尺度煤层瓦斯流动数值模拟方法，根据开采实际分析传统煤层增透措施的增透本质和有效性，提出适合深部煤层瓦斯抽采的增透技术建议，为深部煤层瓦斯抽采和安全生产提供有力支撑。

为解决深部煤层瓦斯有效抽采关键科学问题，本项目以深部多尺度裂隙煤体为研究对象，利用微、细、宏观测试手段，测试了不同尺度条件下煤体孔隙裂隙发育和分布情况，对煤体孔缝结构特征进行了精细表征；开展了瓦斯气体薄膜透过性测试和多尺度煤体瓦斯放散试验，分析了瓦斯多机制流动规律和多尺度流动行为，建立了煤体孔隙瓦斯多机制流动方程和深部煤体瓦斯分形统计多机制流动HTM耦合模型，揭示了深部裂隙煤体瓦斯多机制流动规律；根据开采实际分析传统煤层增透措施的增透本质和有效性，提出适合深部煤层瓦斯抽采的增透技术建议。研究结果表明：煤体内部孔隙和裂隙结构均表现出良好的分形分布特征，随着载荷的增加，煤体内部裂隙体积、分形维数及损伤程度均表现出了三个明显的变化阶段：缓慢减小阶段、缓慢增加阶段和急剧增加阶段。随着瓦斯压力的增大，含瓦斯煤失稳破坏后形成的裂隙网络复杂性与瓦斯压力呈现正相关，瓦斯压力越高，失稳破坏裂隙网络越复杂，裂隙连通性越好，分形维数越大，裂隙密度越大。热应力是导致煤体破坏的根本原因，加热所导致的热应力超过煤体抗拉强度后便会导致新裂隙的产生与扩展。煤层瓦斯流动存在不同的流动机制，当Kn<0.001时瓦斯流动属于达西流，当0.001≤Kn<0.1时瓦斯流动属于滑流，当0.01≤Kn<10 时瓦斯流动属于过渡流，当Kn≥10 时瓦斯流动属于自由分子流。所建立的深部裂隙煤体瓦斯分形统计多机制流动HTM耦合模型，一方面反映了煤体内部孔裂隙分布的分形统计特征，另一方面如实反映了煤层瓦斯流动的多机制流动规律。水力冲孔的瓶颈在于该方法适用于软质煤层，卸压效果的好坏取决于卸煤量的大小，为达到更好的卸压增透效果，应加强其他辅助措施。水力压裂增透措施的瓶颈在于适用于硬质煤体，不适用于软质煤体，增透效果的好坏取决于所形成的裂隙长度和贯通，要达到更好的增透效果，应辅助譬如水力割缝等增强措施。对于软质煤层，建议采用水力冲孔增透措施，同时控制好卸煤量大小，并加强抽采钻孔的护孔和提高封孔效果来提升煤层瓦斯抽采效果；对于硬质煤层，建议采用水力压裂增透措施，同时辅助水力割缝等措施，从而达到更好的煤层卸压增透效果。