不同煤体结构煤的孔隙-裂隙分形特征及其对渗透性的影响

煤的孔隙-裂隙结构特征是研究储层渗透性的关键问题。为了定量描述孔隙-裂隙结构的复杂程度，以黄陇侏罗纪煤田永陇矿区郭家河井田原生结构煤和碎裂结构煤为研究对象，基于压汞实验数据和扫描电镜（SEM）图像，采用Menger分形模型和计盒维数方法，分别计算不同煤体结构煤的孔隙-裂隙分形维数；同时采用不同孔径段的孔隙体积比作为权重值，计算得到孔隙综合分形维数，探讨孔隙-裂隙结构分形维数和渗透率之间的关系。研究结果表明，脆性构造变形作用对孔隙整体复杂性，裂隙孔、渗流孔复杂性以及微观裂隙复杂程度均具有积极改造作用，对吸附孔结构复杂性具有均一化作用；微观裂隙分形维数与渗透率具有较高非线性关系，脆性构造作用改造下形成的碎裂煤，其具有的孔隙-裂隙结构优势配比是决定储层高渗透性的关键。因此，建议优先考虑弱脆性变形的碎裂结构煤为主体的断层、向斜和背斜区域进行煤层气抽采。 

Fractal characteristics of pores and microfractures of coals with different structure and their effect on permeability

The characteristics of pores and fractures in coal are the basis to study permeability. In this study, the micro-pores and fractures of coal samples with different structure taken from Guojiahe coal mine were analyzed using mercury injection experiment and scanning electron microscope. The micro-pores and fractures of intact coal and cataclastic coal samples were quantitatively analyzed by using Menger sponge and box-counting dimension. The comprehensive fractal dimension was calculated by pore volume weights. Based on fractal theory, the relationship between fractal dimension of coal samples and coal permeability have been discussed. The results show that brittle deformation adds complexity of pores, fracture pores, seepage pores and microfractures, while the deformation uniforms the structural characteristics of adsorption pores. Micro-fracture dimension has a nonlinear relationship with permeability. The cataclastic coals deformed by brittle deformation have the suitable ratio of fractal dimensions of pores and microfractures determine their high permeability. Thus, cataclastic coal deformed by weak brittle deformation at fault, syncline and anticline are favorable to gas extraction.