Wen Zhaocui, Jiang Bo, Li Ming, Song Yu, Hou Chenliang
Key Laboratory of Coalbed Methane Resource & Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China.
School of Resources & Earth Science, China University of Mining & Technology, Xuzhou 221116, China.
ACS Omega. 2020 Sep 30;5(40):26023-26037. doi: 10.1021/acsomega.0c03469. eCollection 2020 Oct 13.
The reservoir properties of tectonically deformed coals (TDCs) differ significantly compared with their neighboring primary coals which are also known as unaltered or underformed coals. However, the heterogeneity of nanopores in TDCs under the syncline control has been seldom reported, and also the middle-rank level was minimally investigated to date. Thus, in this paper, the structures and multiscale fractal characteristics of nanopores in middle-rank TDCs under the controlling effect from Panguan Syncline were investigated via high-pressure mercury injection (HPMI), low-pressure CO/N adsorption (LPCO/NGA), and fractal theory. The results show that both the pore volume (PV) and specific surface area (SSA) of macropores increase significantly in the stage of cataclastic-schistose coal. For ductile deformed coals, the PV increases, while the SSA remains stable. The SSA of mesopores increases slightly in the brittle deformation stage, but significantly in the ductile deformation stage. For micropores, both the PV and SSA for TDCs are significantly higher than primary coals. Moreover, the ductile deformation has a more significant promotion effect for the microporous PV and SSA than the brittle deformation. The fractal dimension of the adsorption pore (induced from the Sierpinski model) increases; however, that of seepage pores (Sierpinski model) decreases with the enhancement of tectonic deformation. The fractal dimension for mesoporous (induced from the FHH model, Frenkel-Halsey-Hill) at 2-6 nm keeps stable in the stage of cataclastic-schistose coal but significantly increases in the ductile deformation stage. For mesopores of 6-100 nm, their heterogeneities were also enhanced in the ductile deformation stage. The fractal dimension of 0.3-0.6 nm micropores is close to 3 and changes slightly with the enhancement of tectonic deformation, indicating that the heterogeneity of smaller micropores is stronger than that of larger micropores. The results are of broad interest for CBM exploration and gas outburst prediction.
与相邻的原生煤（也称为未改变或未变形的煤）相比，构造变形煤（TDCs）的储层性质有显著差异。然而，很少有关于向斜控制下TDCs中纳米孔隙非均质性的报道，而且到目前为止，对中变质程度煤的研究也很少。因此，本文通过高压压汞法（HPMI）、低压CO/N吸附法（LPCO/NGA）和分形理论，研究了盘关向斜控制下中变质程度TDCs中纳米孔隙的结构和多尺度分形特征。结果表明，在碎裂片理化煤阶段，大孔隙的孔隙体积（PV）和比表面积（SSA）均显著增加。对于韧性变形煤，PV增加，而SSA保持稳定。中孔隙的SSA在脆性变形阶段略有增加，但在韧性变形阶段显著增加。对于微孔，TDCs的PV和SSA均显著高于原生煤。此外，韧性变形对微孔PV和SSA的促进作用比脆性变形更显著。吸附孔隙（由谢尔宾斯基模型导出）的分形维数增加；然而，渗流孔隙（谢尔宾斯基模型）的分形维数随着构造变形的增强而减小。2-6nm中孔隙（由FHH模型，即弗伦克尔-哈西-希尔模型导出）的分形维数在碎裂片理化煤阶段保持稳定，但在韧性变形阶段显著增加。对于6-100nm的中孔隙，其非均质性在韧性变形阶段也增强。0.3-0.6nm微孔的分形维数接近3，且随构造变形的增强变化较小，表明较小微孔的非均质性强于较大微孔。这些结果对煤层气勘探和瓦斯突出预测具有广泛的意义。
