Abstract: A breakthrough has been achieved in exploration of the trillion-cubic-meter-scale reserves of deep coal-rock gas(some scholars call it as deep coalbed methane) in Ordos Basin. The resource occurrence is primarily controlled by the co-evolution mechanism of macromolecular structure and pore structure in coal-rock. To elucidate this mechanism, coal samples with a continuous maturity [vitrinite reflectance (R_o)ranging from 1.03 % to 1.96 % ]were selected. A comprehensive multi-scale characterization of coal-rock macromolecular structure and pore structure was conducted using ¹³C nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectrometry (FTIR), high-pressure mercury intrusion test, and N₂/CO₂ adsorption experiments. The research results show as follows. (1)As R_o increases from 1.03 % to 1.96 %, the aromatic carbon content rises from 61.56 % to 69.72 %, while the aliphatic carbon content decreases from 28.96 % to 16.77 % . FTIR spectra reveal enhanced characteristic peaks of the aromatic structure and weakened characteristic peaks of the aliphatic structure. (2)Micropores, as the core adsorption space for coal-rock gas, contribute 85.32 % to 96.50 % of the pore volume and more than 99 % of the specific surface area, thus becoming the main occurrence site of methane. (3)The co-evolution of macromolecular structure and pore structure in coal-rock is manifested in the suppression of mesopore development by the breaking of aliphatic chains and the removal of oxygen-containing functional groups, while both aromatization and cyclization promote the accumulation of micropores at the edges of aromatic layers. This results in a significant positive correlation between micropore volume and aromatic carbon content, while mesopore volume shows a positive correlation with aliphatic carbon content. The study discovers the directional evolution mechanism of deep coal-rock reservoirs, characterized by aliphatic structure cracking, aromatic ring cyclization, and micropore development, providing theoretical support for the prediction of deep coal-rock gas "sweet spots".

Key words: Ordos Basin, deep coal-rock, macromolecular structure, pore structure, co-evolution

摘要： 鄂尔多斯盆地深部煤岩气(部分学者称之为深部煤层气)勘探实现万亿立方米级储量规模突破,其资源的赋存主要受煤岩大分子结构-孔隙结构协同演化机制控制。为揭示这一机制,选取成熟度连续分布的煤样[镜质体反射率(R_o)为1.03%~1.96%],综合运用¹³C核磁共振谱、傅里叶变换红外光谱(FTIR)、高压压汞和N₂/CO₂吸附实验开展了多尺度煤岩大分子结构和孔隙结构表征。研究结果表明:①随着R_o从1.03%增至1.96%,芳香碳含量由61.56%上升至69.72%,脂肪碳含量则从28.96%降至16.77%,FTIR谱图显示芳香结构的特征峰增强而脂肪族结构的特征峰减弱;②微孔作为煤岩气的核心吸附空间,贡献了85.32%~96.50%的孔体积和99%以上的比表面积,由此成为甲烷的主要赋存场所;③煤岩大分子结构-孔隙结构协同演化表现为脂肪链断裂与含氧官能团脱落抑制了介孔的发育,而芳构化与环缩合作用则促使微孔在芳香层片边缘富集,导致微孔的孔体积与芳香碳含量呈现出显著的正相关关系,介孔的孔体积则与脂肪碳含量呈正相关。研究揭示了深部煤岩储层"脂肪族结构裂解—芳香环缩合—微孔发育"的定向演化机制,为深层煤岩气"甜点"预测提供了理论支撑。

关键词: 鄂尔多斯盆地, 深部煤岩, 大分子结构, 孔隙结构, 协同演化