An experimental comparison of gas generation from three oil fractions: Implications for the chemical and stable carbon isotopic signatures of oil cracking gas

摘要: Abstract Although oil cracking has been documented as one of the important sources gas in many overmature marine sedimentary basins, chemical and carbon isotopic signatures gases this origin are still open to question. In study a Cambrian crude from central Tarim basin, along with its main separated fractions (saturates, aromatics asphaltenes), were pyrolyzed sealed gold tubes investigate how generated vary composition variation would influence genetic interpretation gas. The results indicate that asphaltenes much drier more enriched 13C than saturates at same level thermal maturity. experimental run 20 °C/h, dryness index (defined volume percentage C1 C1–5) ranges 26.2–90.6% methane isotope change ranging −54.8‰ −35.5‰, whereas is never lower 60.6% for −39.9‰ −32.2‰. Correspondingly, data four samples plot different areas diagrams designed distinguish kerogen gas, such ln(C2/C3) vs. δ13C2–δ13C3 δ13C1 δ13C2–δ13C3, indicating compositional variability could assert an these diagrams. Therefore it prudent bring other geological constraints into consideration avoid misinterpretation. kinetic parameters bulk generation C1–5 fractionation extrapolated conditions 2 °C/Ma initial temperature 50 °C show temperatures those due their activation energies frequency factors. Generation modeled be initiated about 122 °C initiation sample 176 °C. Below 189 °C (EasyRo = 1.8%), yields follow order: aromatics > asphaltenes > crude oil > saturates. At similar maturity levels, compositions significantly samples, order enrichment: oil > saturates, however difference isotopes becomes smaller increasing temperature. This indicates values can cracked oils compositionally diverse, especially early stage generation.