深部低透煤层液氮多级脉冲致裂增渗与驱替瓦斯效应研究

Based on the key scientific problem of enhancing pre-drainage of gas by liquid nitrogen fracturing with low permeability in deep coal seams, this project is planning to use the four-in-one mode that contains theoretical analysis, laboratory test, numerical simulation and field test. A damaging and weakening of liquid nitrogen cycle freeze-thaw coal testing system will be established, the mechanics correlation parameters, pore structure parameters, characterization parameters of AE signal and wave velocity in coal will be measured before and after each freeze-thaw of liquid nitrogen cycle. The damage weakening of coal and the law of deformation and failure of microstructure will be analyzed. To realize the spatial and temporal evolution of coal - induced fissure fractures under the action of liquid nitrogen, a test system of multi-level pulse cracking with liquid nitrogen on gas coal in three axis will be developed independently, which is also used to measure the characteristic parameters of coal fracture expansion and gas desorption. With the action of liquid nitrogen, the corresponding desorption laws of coal will be studied. The relationship among the characteristic parameters of liquid nitrogen multistage pulse, the mechanical parameters of coal, the pore parameters and the characteristic parameters of fracture propagation will be investigated. Meanwhile, the coupling equation of coal deformation and gas desorption seepage under high pressure nitrogen displacement will be established to reveal the effect of liquid nitrogen permeation and displacement gas in coal. Finally obtain the quantitative relationships among the layout parameters of pre-draining borehole, gas extraction parameters and the characterization parameters of liquid nitrogen multistage pulses. All these researches will provide a basis for establishing the method of gas pre-drainage under the condition of liquid nitrogen pulse.

针对深部低透煤层液氮致裂强化预抽瓦斯的关键科学问题，项目拟采用理论分析、实验室试验、数值模拟及现场试验四位一体方式进行研究。研发液氮循环冻融煤体损伤弱化试验系统，测定煤体液氮循环冻融前后的力学参数、孔隙参数以及全过程声发射信号特征参数，研究液氮作用下煤体损伤弱化及微细观结构变形破坏规律；研发真三轴含瓦斯煤体液氮多级脉冲致裂增透及解吸渗流试验系统，测定煤体裂隙扩展及瓦斯解吸渗流特征参数，研究液氮多级脉冲作用下煤体致裂裂隙扩展时空演化规律以及瓦斯解吸渗流规律；探讨液氮多级脉冲特征参数与煤体力学参数、孔隙参数、裂隙扩展特征参数之间的关系，构建高压氮气驱替作用下煤体变形与瓦斯解吸渗流耦合方程，揭示含瓦斯煤体液氮增透与驱替瓦斯效应，获得煤层瓦斯预抽钻孔布置参数及抽采参数与液氮多级脉冲表征参数之间定量化关系，为建立液氮多级脉冲致裂煤体强化预抽瓦斯方法提供依据。

我国大部分深部煤层具有低渗透、高瓦斯含量等特点，采掘前需要进行增透强化预抽瓦斯。液氮具有超低温、高汽化潜热和高相变膨胀的优点，对环境无污染，容易制备且成本低廉。项目通过研发液氮冻融煤体损伤弱化试验系统，测定煤体液氮冻融前后的力学参数、孔隙参数以及全过程声发射信号特征参数，揭示了液氮作用下煤体损伤弱化及微细观结构变形破坏规律。研发真三轴液氮压裂煤体增透试验系统，通过数值模拟研究了液氮多级脉冲作用下煤体致裂裂隙扩展时空演化规律；研究煤体液氮冻融前后瓦斯吸附解吸渗流特性，探讨液氮注入方式与煤体力学参数、孔隙参数之间的关系，构建液氮驱替作用下煤体变形与瓦斯渗流耦合方程，揭示含瓦斯煤体液氮致裂强化抽采瓦斯机理。项目研究对于深化液氮致裂煤体理论与瓦斯解吸渗流理论，提高瓦斯灾害防治与瓦斯资源开发水平等具有一定意义。