低熟页岩干酪根分子结构及生烃特征——以渤海湾盆地辽河坳陷曙光地区古近系沙河街组为例

Molecular structure and hydrocarbon generation characteristics of kerogen in low-maturity shales： A case of the Paleocene Shahejie Formation in Shuguang area， Liaohe Depression， Bohai Bay Basin

马桂丽 陈君青 岳长涛 马跃 王玉莹 庞宏 姜福杰 火勋港

Guili MA Junqing CHEN Changtao YUE Yue MA Yuying WANG Hong PANG Fujie JIANG Xungang HUO

从分子尺度探讨低熟页岩干酪根结构及生烃特征，揭示其生烃路径和生烃模式对低熟页岩干酪根生烃研究及页岩油勘探的重要意义。通过元素分析、固体碳核磁共振谱（C NMR）、X射线光电子能谱（XPS）和傅里叶变换红外光谱（FTIR）等测试分析，研究了辽河坳陷西部凹陷沙河街组四段低熟页岩干酪根的杂原子形态、碳骨架结构、脂肪族和芳香族官能团等特征，构建了化学式为CHONS的干酪根二维分子结构模型。结果表明：该干酪根分子具有脂肪族含量占比高（73.40 %）、芳香族含量占比低和脂肪链较长（亚甲基链碳数为5.04）的特征。干酪根分子的热解生烃反应分子动力学（ReaxFF MD）模拟显示，气态烃（C—C）质量占比在3 500 K温度下可高达41.32 %，轻油组分（C—C）质量占比在3 300 K温度下高达20.75 %，重油组分（C—C）质量占比在2 800 K温度下高达30.22 %，干酪根热解生烃转化率高达61.67 %。页岩干酪根生烃过程经历了结构变化、弱键断裂、强键断裂、二次裂解和缩聚反应等阶段，发生了脂肪族杂原子断键和碳-氢原子断键、芳香族杂原子断键和碳-氢原子断键及芳环脱氢缩聚反应。

Exploring the structure and hydrocarbon generation characteristics of kerogen at a molecular scale and revealing its reaction pathway for hydrocarbon generation and generation model holds great significance for the study on the hydrocarbon generation of kerogen in low-maturity shales and shale oil exploration. A combination of analytical techniques including ultimate analysis， solid-state C nuclear magnetic resonance （C NMR） spectroscopy， X-ray photoelectron spectroscopy （XPS）， and Fourier transform infrared spectroscopy （FTIR）， is applied to investigate the heteroatom morphology， carbon skeleton structure， and aliphatic and aromatic functional groups of kerogen in low-maturity shales from the 4th member of the Paleocene Shahejie Formation in the Shuguang area， Western Sag， Liaohe Depression. Accordingly， a two-dimensional average molecular structure model of kerogen is established with CHONS， which boasts a high proportion （73.40 %） of aliphatics， a low proportion of aromatics， and long aliphatic chains （methylene chain carbon number： 5.04）. The results of the reactive force field molecular dynamics （ReaxFF MD） simulation reveal that the mass fractions of gaseous hydrocarbons （C—C）， light oil components （C—C）， and heavy oil components （C—C） reach up to 41.32 % at 3 500 K， 20.75 % at 3 300 K， and 30.22 % at 2 800 K， respectively， with a conversion rate of kerogen pyrolysis up to 61.67 %. The hydrocarbon generation process of kerogen in the shales progresses through multiple stages， including structural transformation， weak bond breaking， strong bond breaking， secondary cracking， and polycondensation reaction sequentially. During these stages， kerogen molecules undergo the bond breaking of heteroatoms and carbon-hydrogen atoms in both aliphatics and aromatics， as well as dehydrogenation-induced polycondensation reactions of aromatic rings.

10.11743/ogg20250207