冲击荷载下高阶煤的大分子结构及微观\纳观孔隙的动态响应特征及其机制

Using external action to change the coal macromolecule structure and micro/nano-structures in porous coal seam to improve the permeability has practical value to increase the meson extraction ratio in coal mine. Taking high rank coal as samples in this research, the Hopkins bar is used to model the impact load of impact system. The impact experiments under perpendicular/parelell/skew loading conditions with the layers of coal samples are performed to study the dynamic variations of structural parameters of micro/nano-structures of coal samples under loads. With the help of modern measurement technology, the variation of coal macromolecule structure parameters is studied before and after loads. Through investigating the feature variations of microcrystalline structure parameters include the spacing of aromatic layers、diameter and the stack height of basic structural unit(BSU), the chemical force mechanism of impact loading on large molecular structure of coal are explored. Based on the differential variations of micro/nano porous structural parameters of coal including specific surface area、pore volume、pore diameter、connectivity of pore under loading, the variation laws and dynamic response of structural parameters of micro/nano porous configurations of coal are studied. Based on the differential variations of adsorption and desorption, diffusion, permeability of coal under loading, the mechanism of how the coal permeability is varied through the large molecular structure- porosity-adsorption and desorption, diffusion sequence are studied under different loading modes. The research is valuable to increase and improve the theory of coal reservation and to supply theoretic direction to the surface develop and mine extraction of coal gas.

利用外部扰动改变煤的大分子结构及微观\纳观孔隙，改善煤储层的孔渗性，提高煤层气开发和井下瓦斯抽采具有实践价值。项目以高阶煤为例，采用霍普金森杆冲击系统模拟冲击荷载，以与煤样层理呈垂直\水平\斜交的不同方位加载方式开展冲击试验，借助于现代测试手段，对比分析受载前后煤样大分子结构参数的差异，探求微晶结构（BSU）参数（包括芳香层间距、延展度和堆砌度）的变化特征，揭示冲击荷载对煤大分子结构的力化学作用机制；基于受载前后煤样的微观\纳观孔隙结构参数（比表面积、孔容、孔径、孔隙连通性）的差异性变化，研究煤的微观\纳观孔隙形态和结构参数的响应规律；根据受载前后煤的吸附/解吸性、扩散性以及渗透性的差异性变化，系统阐明不同加载模式下，煤的大分子结构—孔裂隙性—吸附/解吸性、扩散性、渗透性的递进作用关系及其实质。研究成果将进一步丰富和完善煤储层强化改造理论，将为煤层气地面开发和井下瓦斯抽采提供理论指导。

课题分别采用卧式/立式霍普金森压杆冲击装置对结构异性煤体进行动态冲击，分析低、中、高应变率下煤体的应力-应变变化规律，获得结构异性煤体的动态力学性能参数；研究了冲击荷载作用下煤岩的微观孔隙结构变化、吸附/解吸特性及渗透性；对比冲击前后煤样压汞、低温液氮及扫描电镜测试数据，结合分形及位错理论，获得了冲击荷载对高阶煤微纳观孔隙结构的影响规律及作用机理；利用炸药对煤样进行爆炸冲击试验，通过改变炸药量控制冲击荷载的大小，并对冲击过后的煤样进行X射线衍射测试，分析了在不同强度冲击荷载作用下煤样微晶结构的变化规律。. 研究结果表明：应变率一定时，垂直于层理方向煤样的峰值应力最大，煤样在不同层理方向的动态应力应变特征表现出很大的差异性。峰值应力随着应变率的增大而线性增大。原煤样的饱和吸附量明显大于冲击载荷下煤样的饱和吸附量，冲击后煤样的压汞滞后环与原煤相比，其滞后环较为宽大，孔隙多以开放孔为主。冲击荷载改善了煤体的孔隙结构，增大了孔隙的连通性。随着冲击荷载的增大，被冲击煤样的渗透率也随之增大。煤样在受到冲击荷载前后，其渗透率受有效应力影响显著。阐释了冲击荷载对高阶煤微纳观孔隙结构的作用机理，即当煤体受到冲击荷载作用时，冲击能量首先会在微晶结构的原始位错处激活位错源，促使位错成核，导致位错塞积，致使微观孔洞成核，当对应滑移系上的位错对进入孔洞以后，就会实现孔洞长大与聚合，形成应力集中效应破坏微观孔隙，最终导致煤体微观孔隙结构参数的变化。与原煤相比，受冲击荷载之后煤样XRD图谱的002峰与100峰均变的更高且陡，衍射峰位置向 值大的一侧偏移；与原煤样相比，受冲击荷载之后煤体的微晶结构参数发生规律性变化，面层间距（d002）表现出减小的趋势，单元堆砌度（Lc）、单元延展度（La）以及（La /Lc）表现出增大的趋势；受冲击煤样的微晶结构更加有序，从微观结构上解释了冲击载荷对煤微晶结构的影响。