The phenomenon that laboratory pyrolysis experiments produce much wetter gases than those in natural reservoirs is a long-recognized and debated problem in the investigation of natural gases in sedimentary basins. In this study, we explore the discrepancy by pyrolyzing a type II kerogen from the Woodford Shale in Oklahoma, compared with the previous results on the produced natural gases from the Arkoma Basin generated from the same source rock (Liu et al., 2019) with the discussion of gas and isotopic compositions at bulk and position-specific (PS) levels. An improved GC-pyrolysis-GC IRMS method is applied for the determination of PS δ¹³C of propane produced in the pyrolysis of the Woodford Shale at Easy %R_o from 0.76 to 3.27. Kinetic and thermodynamic considerations of the chemical and isotopic compositions of the natural and laboratory pyrolysis gases suggest that the generation of light hydrocarbons involves uni-directional cracking reactions, exchange reactions with water, and likely reversible reactions among light hydrocarbons and other H-containing volatiles. After the gas generation in the unconventional Woodford Shale reservoirs, the C₁-C₄ gases might have approached close to chemical equilibrium of C₁-C₃ and isotope equilibrium of C₂-C₁ and C₃-C₁ pairs at their peak temperatures. The capping H for the generation of C₁-C₄ in the Woodford Shale gases appears to have experienced at least partial exchange with the water, while that in the pyrolysis gases is only originated from organic-bound compounds with large kinetic isotope effects (KIE). Our findings indicate that elevated compound-specific and PS δ¹³C values of propane in the wet-gas cracking stage are significantly influenced by the breakdown of the thermally stable compounds (e.g., remaining kerogen, residues). A first synthesis of PS δ¹³C and δ²H isotopic compositions of propane from this study and the literature data suggests relatively similar isotopic structures of propane precursors in kerogens. This study demonstrates that PS isotope analysis of propane can contribute to identifying various geological (e.g., maturation, wet-gas cracking, H exchange, diffusion) and biodegradation processes.

实验室热解实验产生的气体比天然储层中的气体更湿的现象是沉积盆地天然气研究中长期以来公认和争论的问题。在这项研究中，我们通过热解俄克拉荷马州伍德福德页岩中的 II 型干酪根来探索差异，并与之前从同一烃源岩产生的阿科马盆地产生的天然气的结果进行比较（Liu 等人，2019 年）在体积和特定位置 (PS) 水平上讨论气体和同位素组成。改进的 GC-热解-GC IRMS 方法用于测定Woodford 页岩在 Easy %R _{o热解过程中产生的丙烷的 PS δ} ^{13 C}从 0.76 到 3.27。对天然和实验室热解气体的化学和同位素组成的动力学和热力学考虑表明，轻烃的产生涉及单向裂解反应、与水的交换反应，以及轻烃和其他含 H 挥发物之间可能发生的可逆反应。非常规伍德福德页岩储层产气后，C ₁ -C ₄气体可能已接近C ₁ -C _{3化学平衡和}C ₂ -C ₁和C ₃ -C ₁同位素平衡对在它们的峰值温度。_{伍德福德页岩气中产生 C 1} -C ₄的封顶 H似乎至少与水发生了部分交换，而裂解气中的封顶 H 仅来源于具有大动力学同位素效应的有机结合化合物（KIE ）。我们的研究结果表明，湿气裂解阶段丙烷的化合物特异性和 PS δ ^{13 C 值升高受到热稳定化合物（例如，剩余的干酪根、残留物）分解的显着影响。}PS δ ¹³ C 和 δ ^{2的第一次合成}本研究中丙烷的 H 同位素组成和文献数据表明干酪根中丙烷前体的同位素结构相对相似。这项研究表明，丙烷的 PS 同位素分析有助于识别各种地质（例如成熟、湿气裂解、H 交换、扩散）和生物降解过程。