Characteristics and Formation Mechanism for the Saline Lacustrine Oil from the North Dongpu Sag

Abstract

Abstract:

Conventional geochemical methods including GC/MS, Rock-eval combined with ESI FT-ICR MS and compound specific carbon isotopic analysis are used to reveal hydrocarbons generation and migration style for the saline lacustrine oils from the Wenmingzhai and Weicheng Oilfield in the North Dongpu Sag, Bohai Bay Basin, which is still unclear enough up to date. It was observed that the crude oils bearing typical characteristics of saline lacustrine oils such as predominance of phytane to pristine and C₃₅-hopane to C₃₄-hopane, enrichment of gammacerane, and low extent of isomerization of steranes. The oils are also featured by two-stage carbon isotope distribution of n-alkanes:the δ¹³C for the n-alkanes with carbon number less than 21 is ranged in -29‰ to -28‰, while those larger than 21 is ranged in -31‰ to -29‰, which is different from “parallel lines pattern” for the saline lacustrine oils from the Western Qaidam Basin, suggesting different paleoenvironment and precursors for the n-alkanes in the North Dongpu Sag. Abundant NSO’s compounds including S₁,S₂,O₁S₁,N₁,O₁,O₂ and O₃ with low extent of aromatization are detected from the oils analyzed, which were predicted having a close genetic relationship with the immature oils in the area. A detailed oil-oil and oil-source rock correlations showed that the crude oils analyzed are primarily derived from Es₃ and Es₄ source rocks with burial depth larger than 3 000 m. It was suggested that the crude oils are mixed by different source rocks with varied thermal maturity, which would be instructive for the further petroleum exploration in the area.

Key words: Dongpu Sag, saline lacustrine facies, immature oil, oil-source rock correlation, hydrocarbon accumulation with mixed sources

CLC Number:

P588
TE122.1

ZHANG Hongan, LI Sumei, XU Tianwu, PANG Xiongqi, ZHANG Yunxian, WAN Zhonghua, JI Hong. Characteristics and Formation Mechanism for the Saline Lacustrine Oil from the North Dongpu Sag[J]. Geoscience, 2017, 31(04): 768-778.

Figures/Tables 10

Fig.1 Regional tectonic map of the North Dongpu Sag and partial samples distribution

Table 1 Basic geochemical parameters of the oils analyzed in the North Dongpu Sag

Fig.2 Total ion chromatogram (TIC) of saturated fraction in the oils analyzed in the North Dongpu Sag

Fig.3 Partial m/z217、m/z191 mass fragmentograms of saturated hydrocarbon fractions of the oils analyzed in the North Dongpu Sag

Fig.4 Distribution of NSOs compounds in the oils analyzed by ESI FT-ICR MS

Fig.5 Compound specific carbon isotope of n-alkane in the oils from the North Dongpu Sag and the Western Qaidam Basin

Fig.6 Total ion chromatogram (TIC) of saturated fraction in the oil-sand and potential source rocks from well Wei18-5

Fig.7 Partial m/z217、m/z191 mass fragmentograms of saturated hydrocarbon fractions of the oil-sand and potential source rocks from Well Wei18-5 in the North Dongpu Depression

Fig.8 Correlation of oil-sand and the adjacent potential source rocks about maturity and the relevant parameters for the samples from well Wei18-5 in the North Dongpu Sag

Fig.9 Correlation of oil-source rocks about maturity and the relevant parameters for the samples from the North Dongpu Sag

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