Hydrocarbon Sources and Charging History of the Ordovician Reservoirs in the Zhuangxi Buried Hill, Jiyang Depression

Hydrocarbon sources and charging history remain uncertain in the Ordovician carbonate reservoirs of the Zhuangxi Buried Hill. We integrated biomarker analyses of eight crude oil and reservoir rock extract samples from seven wells with fluid inclusion observations, microthermometry, pressure–volume–temperature modelling and burial and thermal histories. Oil source comparisons used compiled reference ranges supplied by Sinopec Shengli Oilfield, rather than source rock measurements made by the authors. Exploratory PCA and Ward clustering summarised compositional relationships among the samples. Biomarker comparisons favour affinities with the lower submember of the third member (Es3x) and upper submember of the fourth member (Es4s) of the Shahejie Formation in the Gubei Sag, while other contributions remain possible. Contrasts among Majiagou oils suggest possible local variation in source affinity, although maturity and alteration may also contribute. Inclusion age estimates for four wells fall mainly within Guantao and Minghuazhen deposition during reburial after the Dongying Movement, with some estimates extending into the Quaternary. Their ranges describe the spread of individual inclusion estimates and may partly reflect homogenisation temperature dispersion. Palaeopressure coefficients range approximately from 0.8 to 1.2 and mostly cluster around unity under the 9.8 MPa/km reference gradient. These estimates depend on the empirical temperature correction, burial and thermal histories, and inclusion preservation. The observations are consistent with a regional model involving possible entry through faults and unconformity windows, but they do not establish specific migration routes or pathway connectivity as the principal control on hydrocarbon distribution.