目的目的为深入研究中低阶煤中孔裂隙结构和孔径分布形态,方法方法利用压汞、低温液氮吸附和低场核磁共振试验,结合分形维数分别对新疆艾维尔沟1890煤矿低阶煤(XJ)和鹤壁八矿中阶煤(HB)的孔隙结构和孔径分布进行联合表征,并提出一种基于优势区间的全孔径分形维数表征方法,即孔径r<140nm时,使用低温液氮吸附法的FHH模型表征;140≤r<1000nm时,使用核磁共振模型表征;r≥1000nm时,使用压汞法的Menger海绵模型表征。结果结果结果表明:XJ的中/大孔主要由开放孔构成,微/小孔主要由封闭孔和半封闭孔构成,其中,大孔对孔容的贡献率最高,达到94%以上,中孔是孔比表面积的主要贡献者,贡献率为40.58%,微/小孔和中孔较发育,大孔几乎不发育,微/小孔的孔隙连通性较差,中大孔隙的连通性较好;HB孔隙主要由半封闭孔构成,其中孔容中大孔占比最高,占比达97%以上,孔比表面积主要由小孔贡献,贡献率为58.33%,以微/小孔发育为主,中孔、大孔和裂隙相对不发育,孔隙连通性较差;低温液氮吸附法的DFT模型可以得到XJ最发育的孔径为10~12nm,HB最发育的孔径为1~4nm;r<140nm时,HB的内分形维数明显大于XJ的,此孔径范围内HB的非均质性比XJ的更强,孔隙结构更复杂;r>140nm时HB的分形维数小于XJ的,此孔径范围内XJ的孔隙结构比HB的更复杂。结论结论研究结果揭示了中低阶煤储层孔隙分布规律,为中低阶煤层的裂隙扩展和瓦斯运移提供理论指导。

Objectives In order to further study the pore structure and distribution of middle and low rank coal, Methods mercury injection, low temperature liquid nitrogen adsorption and low field nuclear magnetic reso⁃nance experiments were used to jointly characterize the pore structure and pore size distribution of the low rank coal in Aiweilgou 1890 coal Mine (XJ) and the middle rank coal in Hebi No.8 Coal Mine (HB), combined with fractal dimension. A full-aperture fractal dimension characterization method based on dominant interval is proposed, namely: the fractal dimension of r<140 nm is characterized by FHH model using liquid nitrogen method; The fractal dimension of aperture 140~1 000 nm was characterized by NMR model. The fractal dimen⁃sion of aperture r>1 000 nm was characterized by the Menger sponge model of mercury injection method. Re⁃sults The results show that: The large and medium pores of low-rank XJ coal are mainly composed of open pores, and the small pores are mainly composed of closed and semi-closed pores. Among them, the contribution rate of large pores to pore volume is the highest, reaching more than 94%, and the contribution rate of medium pores is the main contributor of pore specific surface area, accounting for 40.58%. The small pores and medium pores are relatively developed, while the large pores are almost undeveloped, and the pore connectivity of small pores is poor. The connectivity of large pores is good. The pores of HB medium-rank coal are mainly composed of semi-closed pores, in which the proportion of large pores is the highest, accounting for more than 97% of the pore volume. The specific surface area of pores is mainly contributed by small pores, with a contribution rate of 58.33%. Small pores are mainly developed, while medium pores, large pores or cracks are relatively undevel⁃oped, and the pore connectivity is poor. The DFT model of liquid nitrogen method shows that the most devel⁃oped pore diameter of low-rank XJ coal is 10~12 nm, and that of mid-rank HB coal is 1~4 nm. The fractal di⁃mension of HB mid-rank coal is significantly larger than that of XJ low-rank coal in the r<140 nm pore size range, and the heterogeneity of HB mid-rank coal is stronger than that of XJ low-rank coal in this pore size range, and the pore structure is more complex. The fractal dimension of the mid-rank coal of HB is smaller than that of the low-rank coal of XJ in the pore size range of r>140 nm, and the pore structure of the low-rank coal of XJ is more complex than that of the mid-rank coal of HB. Conclusions Research achievements provides theo⁃retical guidance for the fracture expansion and gas migration in the middle and low-rank coal seam.