钻孔水射流冲击破煤岩特性及增透作用机制研究

Borehole-based water injection technique has been one of the most critical stimulation approaches to increase the permeability of coalbed methane (CBM) reservoirs and enhance the methane drainage performance. In this project, based on the industrial application of the permeability-enhancement water injection technique, the mechanism of permeability enhancement based on coal-rock fracturing using water jet in boreholes is investigated through theoretical analysis, numerical modelling and physical experiments. First, the impact of water jet on the microscopic coal structure will be studied by analyzing the pore size characterization of the high outburst-prone coalbed in north China. Then the macroscopical effect of water jet on the borehole damage will be studied by gaining understanding on the impact dynamics and coal/rock fracturing mechanisms of the borehole-based water injection. Based on the understanding of stress and fracture evolution before and after water injection, a new permeability model will be developed. Meanwhile, the key parameters and controlling factors on water jet will be analyzed to characterize the fracturing process of the porous coal. The effect of water jet on the coal properties is investigated. The implementation of this project can advance a revolutionary theory to promote the improvement and optimization of the related technologies, and provide a guidance for borehole design and permeability-enhancement-effectiveness evaluation.

钻孔水射流增透技术是当前改造煤储层、促进瓦斯抽采的重要手段之一。本项目以钻孔水射流增透技术的工程应用为背景，采用理论分析、数值模拟、实验研究相结合方法，进行水射流在钻孔内的冲击破煤岩特性及增透作用机制研究：探索华北聚煤区内低透气性煤层的特征参数及其对水射流的冲击响应规律，阐明水射流对煤体结构的细观影响；探索钻孔内水射流的冲击动力学特性及破煤岩机制，阐明水射流对钻孔损伤的宏观影响；探索水射流作用前后钻孔煤体的裂隙演化与径向卸圧规律，构建基于水射流的钻孔增透模型，阐明水射流对钻孔抽采的增透影响；探索水射流作用下煤体损伤的关键参数及主控因素，探究含孔煤体的受载损伤特性和裂隙演化规律，构建区域煤体的多因素协同增透机制，阐明钻孔水射流增透对区域煤体的影响。该项目的实施可以弥补现有技术的理论短板，推动相关技术工艺改进和装备优化，并对区域煤体抽采钻孔设计和增透效果评价提供指导。

利用水射流切割、破坏煤岩体，是目前我国煤矿实现煤层卸圧增透的主要技术途径之一。本项目以钻孔水射流增透技术在矿井瓦斯抽采中的应用为工程背景，以我国华北聚煤区内的深部低透煤层为研究对象，采用理论分析、数值模拟、实验研究等方法，围绕钻孔环境下水射流的冲击破煤岩特性与卸压增透作用机制开展研究。通过研究，得到了华北聚煤区内低透气性煤层的物性参数特征，分析了不同变质程度、不同瓦斯等级、不同埋深煤样的孔隙结构与吸附特性，阐明了煤样孔隙结构对水射流冲击的响应规律；搭建了水射流冲击实验系统，得到了圆形喷嘴水射流流场及形态结构特征，掌握了水射流冲击钻孔表面和平面的差异，揭示了钻孔内水射流的冲击动力学特性和破煤岩机制；阐明了钻孔水射流冲击对瓦斯的驱替作用，掌握了水射流冲击损伤煤体的关键参数及主控因素，揭示了含孔煤体的受载损伤特性和裂隙演化规律；开发了一种大直径瓦斯抽采钻孔成孔装置和方法，提出了水射流钻孔的径向渗透率模型，构建了水射流钻孔“变结构-驱瓦斯-加损伤-扩卸压-增裂隙-强扰动”的六协同增透机制，并探索了水射流钻孔的尺寸效应。研究成果为水射流技术在深部低透气性煤层瓦斯灾害治理和高效抽采方面的应用奠定理论基础。项目圆满完成了计划书中规定的研究内容，取得了预期研究成果，在核心及以上期刊发表论文7篇、已录用待发表论文2篇；申请国家发明专利5项、其中已授权3项；正在培养4名硕士研究生。