oa Formation of Oil Cracking Gas in Central Sichuan Basin: Insights from Both Closed and Semi-Open Gold Tube Pyrolysis Experiments

In this study, a Cambrian sourced oil sample and its SARA (saturates, aromatics, resins and asphaltenes) fractions were pyrolyzed in closed systems to investigate the effects of oil fraction composition on the molecular signature and methane carbon isotope composition of the generated gas. Meanwhile, the oil sample and its asphaltene fraction were further pyrolyzed in stepwise, semi-open system to investigate how possibly the geological openness affects the generation potential and geochemical signatures of the gases from the cracking of oil and asphaltenes. Our results reveal that it may be quite common for early-generated oil cracking gas to be lost in overmature gas reservoirs, leading to the accumulation of late gas with extremely low gas wetness and d13C1 values even heavier than the d13C values of their parent oils.