深部复杂煤层射流造缝导向压裂裂缝起裂及扩展机理

With increasing mining depth,permeability of coal is getting lower and lower.How to dramatically enhance permeability of coal is the key to realize efficiency of coalbed methane mining and the safety of coal mining.Hydraulic fracturing of oil and gas fields have been introduced to the development of coalbed methane.Due to characteristics of conservation is difference between oil stratum and coal seam,fracture's developing is unordered and severely damaged seam.As a result,hydraulic fracturing increased permeability of coal is limited and seam is difficult to support when coal is mined. So we introduced a method that could improve dramatically permeability by controlling crack propagation and extending range of hydraulic fracture. The method should be done as follows; firstly, boreholes were drilled reasonably and slotted by high pressure water jet. And then, four or more boreholes drilled around the first borehole, these boreholes were also slotted by high pressure water jet. Finally, we injected high pressure water into first borehole after sealing all boreholes. The slitting slotted by water jet could control crack initiation site and guide fracture's propagation, that is, the fracture extended to surrounding borehole. The main contents were as follows; Creating a moisture content of coal rock constitutive equation and failure criterion based on the study of rock mechanics properties of deep coal.Analyzing the law of crack initial and propagation after figuring out plastic zone of slitting tip and mechanic character of coal around slitting. Besides, we would develop a method of how to control crack propagation in deep and disadvantaged coal seam. Then, mechanisms of crack closure and improving permeability of hydraulic fracture by combined with high pressure water jet slotting would be developed. Finally, we would research technology of efficient hydraulic fracture and experimenting in type of diggings.

随着煤矿开采深度的不断延深，煤层透气性越来越低，如何大幅度增强煤层透气性是实现煤层气井下高效抽采和煤炭安全开采的关键。油气领域的水力压裂技术已被引入煤矿井下煤层气的开发，但由于油气地层与煤层气赋存特征的不同，煤矿井下水力压裂出现裂缝无序扩展以及煤层顶底板破坏严重，导致增透范围小和后续煤炭开采时顶底板支护困难。本项目提出利用水射流切割缝槽导向水力压裂，促使裂缝有序、大范围扩展，以大幅度增强煤层透气性的方法。主要研究内容为：在研究深部复杂煤岩体力学特性的基础上，建立含水煤岩体本构方程和破坏准则；分析水射流造缝对煤体应力场的变化规律，揭示不同煤层赋存条件下射流造缝后煤体起裂及裂缝扩展机理；从裂缝闭合应力敏感性角度研究射流造缝对煤体应力场和裂缝闭合的影响规律，揭示水射流造缝导向水力压裂增强煤层透气性的机理，开发射流造缝导向压裂增透工艺及装备，并在典型矿区现场试验。

针对煤矿井下水力压裂裂缝无序扩展以及煤层顶底板破坏严重，导致增透范围小和后续煤炭开采时顶底板支护困难等难题，项目提出利用高压水射流切割煤体形成定向缝槽进行导向压裂，促使裂缝有序、大范围扩展，以大幅度增强煤层透气性的方法。围绕射流造缝导向压裂裂缝起裂及扩展机理这一关键科学问题，采用理论分析、相似物理实验和数值模拟相结合的研究方法，通过分析压裂过程中含水瓦斯煤岩体的物理力学特性，建立了含水煤岩体本构方程和破坏准则，为水射流破碎煤岩提供理论基础；分别采用弹性力学、断裂力学和土力学理论，建立了不同煤层赋存条件下造缝导向压裂裂缝起裂及扩展理论模型，揭示了射流造缝导向压裂起裂及裂缝扩展规律；根据多相流体力学和多孔介质流体动力学理论，构建了导向压裂过程中水-瓦斯耦合运移模型，获得压裂后煤层瓦斯运移富集规律，揭示了射流造缝导向致裂煤层的增透机理，对瓦斯抽采钻孔的优化布置具有指导意义；在此基础上研发了射流造缝、钻孔布置、封孔和水压致裂等射流造缝导向压裂增透装备及工艺，并在松藻矿区进行现场试验；与传统水力割缝和压裂相比，煤层气平均抽采量提高3~5倍，预抽钻孔数量减少27%以上。项目研究成果获教育部科技进步一等奖1项，出版著作1部；发表学术论文21篇，其中SCI检索11篇、EI检索10篇；申请发明专利3项；培养毕业博士生4人，硕士研究生4人（优秀硕士论文1篇）。项目申请人于2016年获得国家自然科学基金委杰出青年基金资助(No. 51625401) 和入选第二批国家“万人计划”科技创新领军人才，并在国际、国内会议上做特邀及大会报告12次。