μCT技术研究煤的孔隙结构和分形特征

Pore structure and fractal characteristics of coals by μCT technology

煤的孔隙结构是影响煤中气体吸附和渗流的一个重要因素。从实现精细化、无损化和定量化入手,应用μCT 225kVFCB型高精度CT试验分析系统,通过显微CT切片,提取研究了4个煤样孔隙分布特征,讨论了煤级、煤显微组分和灰分对煤孔隙结构的影响程度。采用公约数网格序列盒维数法定量表征了孔隙结构的复杂程度和不规则性,探讨了孔隙率、渗透率和分形维数的关系。研究表明,研究煤样的孔隙分布总体受煤显微组分含量控制,同时煤中矿物充填作用在一定程度上降低了煤的孔隙率、平均孔径和孔隙数量。煤孔隙分形维数D的变化与孔隙分布特征密切相关,有效地反映了孔隙结构的非均质性。孔隙率、渗透率与分形维数呈现显著的幂指数正相关关系。由此指示,基于显微CT切片的煤孔隙分形维数可作为煤储层孔隙特征和渗透性评价的定量指标之一。

Pore structure is one of important factors affecting the gas adsorption and transportation of coal .The advanced ,nondestructive ,and quantitative characterization of pore distribution for 4 coal samples was obtained through a micro‐CT system μCT225kVFCB .The influence of coal rank ,maceral composition and ash content on pore structure was also discussed .The sequence of divisors algorithm of box‐counting method was applied to quantify the complex and irregular pore structure and the relationship between porosity ,permeability and fractal dimension was explored .The results show that the maceral composition contents control the pore distribution for the coal studied .The mineral‐matter filling also contributes to the reduction of porosity ,the mean pore diameter and pore numbers . The variation of fractal dimension is closely related to the characteristics of pore distribution ,which effectively reflects the heterogeneity of pore structure .There is a strong positive correlation between porosity ,permeability and the fractal dimension . Hence ,the fractal dimension of coals obtained by μCT segmentation method can be used as one of the quantitative indexes for evaluation of pore characteristics and permeability of coal reservoir .