Thermal Evolution of Adsorbed/Occluded Hydrocarbons inside Kerogens and Its Significance As Exemplified by One Low-Matured Kerogen from Santanghu Basin, Northwest China

摘要

Organic compounds-could be adsorbed and even occlutled within the macromolecular Structures of kerogen. Studies concerning thermal evolution of adsorbed/occluded hydrocarbons inside kerogen will be helpful in understanding its structural characteristics and-evolution features and estimating the-effectiyeneSs.olaclsorbed and occluded-fractions. In this work,. adsorbed and occluded hydrocarbons have been released from low-matured kerogen from the upper Permian Lucaogou formation of Santanghu Basin, north-West China; and from its pyrolysis residues by solvent extraction and oxidative treatment, respectively. The results showed that some n-alkanes, terpanes,and stetanes were detected from both adsorbed and occluded fractions. Series of even-carbon-numbered n-alk-(1)-enes were also determined from the occluded components. The early stage of thermal evolution showed similarities in biomarker features for both,adsorbed and occluded hydrocarbons; however, variations were noted in biomarker composition's with increasing thermal levels. The obvious changes Of C21-22 pregnane/C27-29 sterane ratios from adsorbed to occluded fractions at high thermal evolution suggested that high concentrations of pregnane (containing homopregnane) in soluble components in highly or overly mature stage may be mainly derived from the corresponding components covalefitly bound within kerogen.,Occluded components exhibited stronger thermal stability than adsorbed components. This study showed that evaluation,of the thermal evolution characteristics of kerogens/source rocks based on bioniarkers compositions from the adsorbed components at highly to overly matured stages was difficult, while we hope this kind of assessment of kerogens/source rocks can be achieved from occluded components.