Research Advances in Separation Technologies and Petroleum Geochemistry Applications of Asphaltene-Occluded Hydrocarbons

The self-assembled structures of asphaltenes can physically occlude primary small-molecule hydrocarbons and protect them from later secondary alteration, making asphaltene-occluded hydrocarbons important information carriers in petroleum geochemistry. Efficient and nondestructive separation of these occluded hydrocarbons is a prerequisite for high-precision analysis. This paper reviews four major separation techniques: multistep elution, selective oxidative degradation, dispersive solid-phase extraction, and catalytic hydropyrolysis. Multistep elution removes surface-adsorbed hydrocarbons through solvent swelling, but its separation depth is limited, making it more suitable as a pretreatment method. Selective oxidative degradation releases occluded hydrocarbons by cleaving heteroatom bonds, but may introduce altered products and oxidative by-products. Dispersive solid-phase extraction, based on the Yen-Mullins model, achieves nondestructive release of occluded hydrocarbons through aggregate disaggregation controlled by asphaltene concentration (0.1–1.0 mg/mL), showing relative advantages in information fidelity and operational controllability. Catalytic hydropyrolysis mainly releases covalently bound biomarkers through cleavage of C–C bonds under high-temperature hydrogenation conditions, but signals of physically occluded and chemically bound hydrocarbons are difficult to distinguish. In terms of applications, occluded hydrocarbons support oil-source/oil-oil correlation of biodegraded crude oils and reveal multistage charging patterns in complex reservoirs of the Tarim Basin. Owing to the thermal-evolution hysteresis, occluded hydrocarbons also provide earlier maturity information for evaluating high- to over-mature source rocks. In addition, special biomarkers such as n-alk-1-enes and terpenes detected in occluded hydrocarbons provide new molecular windows for identifying organic matter sources and reconstructing paleoenvironmental conditions. At present, reliability verification of separation techniques, calibration of the maturity hysteresis window, and confirmation of the universality of special biomarkers remain key issues. Future studies should focus on technical integration and standardization, molecular-level characterization and simulation, and expanded applications to emerging scientific questions.