Hydrocarbon generation kinetics of salinized lacustrine source rocks in the upper Cretaceous-Paleocene South Yellow Sea Basin, offshore eastern China

Abstract

Saline lacustrine source rocks have different enrichments in organic matter and hydrocarbon generation processes as compared with source rocks formed in freshwater and marine basins. We investigated the hydrocarbon generation kinetics of saline lacustrine source rocks and the physical properties of petroleum using immature source rocks from the Upper Cretaceous Taizhou Formation and Paleocene Funing Formation in the South Yellow Sea Basin. The source rocks were analyzed using PhaseKinetics approach.Our main results are as follows. (1) Compared with source rocks from freshwater and marine basins, the source rocks in the South Yellow Sea Basin have the same organofacies (i.e., generating Paraffinic-Naphthenic-Aromatic low wax oils) and a lower bulk activation energy (frequency factors of A = 9.66 × 1012 and 4.61 × 1012 s−1, with a dominant activation energy at 51 and 50 kcal/mol), with oil window conditions of 128–155°C and 98–146°C). (2) Compositional kinetic modelling indicates that the generated gas consists mainly of C1, C2, and C3 compounds, while the liquid phase is dominated by C7-15 and C16-25 compounds. (3) The physical properties of the two suits of source rocks show that the saturation pressure, gas/oil ratio and formation volume factor vary with maturation. The pressure−temperature envelope of different maturities defined by these experiments allowed their phase behavior to be predicted, with a liquid phase being generated by the Taizhou Formation, and an oil−gas phase fluid being transiently generated by the Funing Formation.These results provide new insights into the hydrocarbon generation kinetics of saline lacustrine source rocks, which are relevant to regional shale oil exploration.