Hydrocarbon gas generation from pyrolysis of extracts and residues of low maturity solid bitumens from the Sichuan Basin, China

Two sets of pyrolysis experiments were performed on bitumen “A” (BA) and extracted organic matter (ER) from low-maturity solid bitumen at heating rates of 2 °C/h and 20 °C/h in confined systems (gold capsules). The main observations can be listed as follows: (1) BA and ER have high generation potential of hydrocarbons and were a significant secondary hydrocarbon source. (2) Both have similar evolutionary characteristics of hydrocarbon gas generation, and have high C1/C1-5 values than those from an Ordovician normal oil. Ea distributions of the methane generated from pyrolysis of BA and ER is far lower than that of Ordovician normal oil. (3) The evolution of stable carbon isotope values of individual hydrocarbon gases can be divided into three stages. Plots of ln C1/C2 versus ln C2/C3, δ13C1-δ13C2 versus ln(C1/C2) and δ13C2-δ13C3 versus ln(C2/C3) clearly illustrate the characteristics of hydrocarbon gases generated from BA and ER at different thermal maturity stages. (4) Basin modelling reconstructions of the hydrocarbon generation history of BA and ER in Sinian and Cambrian strata respectively indicate: Hydrocarbon gases generation from ER started in the Middle Jurassic, and ended in the Early Cretaceous with a maturity equivalent to Easy%Ro ≈ 2.2%. The final conversion rate of C1-5 and C1 are 0.71 and 0.48, respectively. Hydrocarbon gas generation from BA started in the Early Jurassic, and ended in the Early Cretaceous with an Easy%Ro ≈ 3.0%. The final conversion rate of C1-5 and C1 are 0.90 and 0.81, respectively.