Enrichment types and hydrocarbon composition characteristics of shale oil in the northern part of Dongpu Sag, Bohai Bay Basin: a case study of the third member of Paleogene Shahejie Formation of well Wen 410

Abstract

To reveal the oil-bearing characteristics and hydrocarbon composition of shale oils in the third member of Shahejie Formation in the northern part of Dongpu Sag, Bohai Bay Basin, analysis and testing were carried out by the means of frozen-craching followed by pyrolysis, 3D quantitative fluorescence test, GC-MS and thin section observation. Two shale oil enrichment types including interlayer type and fracture type are mainly developed in the third member of Shahejie Formation of well Wen 410. The hydrocarbon mainly occurres in inter-granular pores and micro-fractures, and effective pore-fracture combination is the key to the efficient enrichment of shale oil. The hydrocarbon composition of rock extracts is mainly characterized by n-alkanes with low carbon numbers, and the regular steranes of C27-C28-C29 show a V-shaped distribution, reflecting that the sources of organic matter are mainly terrestrial higher plants and lower aquatic organisms. The high content of gammacerane and the low Pr/Ph ratio indicate that the sedimentary environment in this area is mainly a saline reducing environment. C3122S/(22S+22R), Ts/(Ts+Tm), C29ααα20S/(20S+20R), C29ββ/(αα+ββ) and other biomarker parameters indicate that the source rocks are at mature stage.

Keywords

• hydrocarbon composition
• occurrence form
• shale oil
• shahejie formation
• paleogene
• dongpu sag
• bohai bay basin