构造变形对烟煤级构造煤微孔-中孔的作用

煤作为一种复杂的天然多孔性固体物质,其纳米级孔隙对煤层气的储集和运移有着重大影响。我国受成煤盆地多期次构造运动影响,煤层普遍发育不同破坏类型的构造煤,构造煤纳米级孔隙结构在构造变形作用下发生重要变化,这一变化不仅影响着煤层瓦斯的储集和赋存状态,同时也对煤与瓦斯突出预测和煤层气开采具有重要意义。采集首山一矿和义安矿不同变形程度构造煤样品,基于低温液氮吸附(2～50 nm)和二氧化碳吸附(2 nm)实验,利用多重分形理论分析了构造变形对煤的微孔-中孔结构的影响。结果表明煤样微孔和中孔均具有多重分形特征,微孔广义分形维数谱宽D_(10-)～D_(10+)和奇异指数α_0随变形程度的增加整体递增,中孔则先降低后增加。弱变形阶段,微孔信息维数D_1和赫斯特指数H逐渐降低而多重分形奇异谱谱宽Δα逐渐增加,中孔D_1和H逐渐增加而Δα逐渐降低。强变形阶段,微孔D_1,H和Δα均没有发生明显变化,中孔D_1和H明显降低,Δα明显增加。分析构造煤孔隙特征与煤体破坏强度的关系,弱变形阶段,构造变形作用导致煤的微孔结构趋于复杂,孔隙连通性较差,中孔结构趋于简单,归因于官能团脱落以及应力作用下部分中孔结构的收缩。强变形阶段,微孔结构差异依然较强,中孔结构差异则由弱变强,这与强构造应力作用下形成大量的分子间孔、缺陷以及气孔有关。

Effects of tectonic deformation on micropore mesopore of bituminous deformed coal

Coal is a complex natural porous solid substance and its nano scale pore has a significant impact on the storage and migration of coalbed methane.Influenced by multi stage tectonic movements in coal forming basins in China,different types of deformed coal are widely developed in coal seams,and the nano pore structure changes greatly under the action of tectonic deformation.This change not only affects the state of gas reservoir and occurrence in coal seams,but also has a significant impact on coal and gas outburst prediction and coalbed methane extraction.Samples of deformed coal with different deformation degrees in Shoushan No.1 and Yi’an Mines were collected.Based on the experiments of low temperature liquid nitrogen adsorption (2-50 nm) and carbon dioxide adsorption (<2 nm),the effects of tectonic deformation on the micropore mesopore of coal were analyzed by using multifractal theory.The experimental results show that both micropore and mesopore of coal samples have multifractal characteristics.The spectrum width of generalized fractal dimension D10--D10+ and singularity exponent α0 increase with the increase of deformation degree,while the mesopore decreases first and then increases.At the weak deformation stage,the information dimension D1 and Hurst exponent H of micropore gradually decrease,the multifractal singular spectrum width Δα gradually increases,and the mesopore D1 and H gradually increase,while Δα gradually decreases.At the stage of strong deformation,there are no significant changes in micropore D1,H and α,while the mesopore D1 and H decrease and Δα increases significantly.The relationship between pore characteristics of deformed coal and the strength of tectonic deformation is analyzed.At weak deformation stage,tectonic deformation promotes the increase of complexity and the decrease of connectivity in micropore,while the structural differences of mesopore decreases,which is attributed to the loss of functional groups and the shrinkage of some mesoporous structure under stress.At the stage of strong deformation,the micropore structural differences is still strong,while the structural differences of mesopore increase,which is related to the formation of intermolecular pore,defect and gas pore under strong tectonic stress.