Geochemical Characteristics and Source Correlation of Low-mature Oil from the Tengeer Formation (2nd Member) in the Saihantala Sag, Erlian Basin

doi:10.19657/j.geoscience.1000-8527.2020.100

Abstract

Abstract:

The Saihantala Sag is located in the western Tengeer depression of Erlian Basin, and contains low-mature oil in the Erlian Basin. The geochemical characteristics and oil source correlation of the low-mature crude oil and oil sandstone samples from the Lower Cretaceous Tengeer Formation (2^nd member) in the Saihantala Sag were studied, by using organic geochemical and biomarker analyses. The low-mature oil from the Tengeer Formation (2^nd member) is characterized by having relatively low content of saturated hydrocarbon, and relatively high content of non-hydrocarbon and asphaltene. The distribution of n-alkanes is of pre-peak type, and the main peak carbon is C₂₁, C₂₃. The Pr/Ph is low (0.29 to 0.58), Pr/nC₁₇ is relatively low (0.29 to 0.59), Ph/nC₁₈ is relatively high (0.57 to 1.37), and C₂₉ 20S/(20S+20R) of sterane is 0.27 to 0.40, C₂₉ββ/(αα+ββ) of sterane is 0.29 to 0.39, the gammacerane index is mainly 0.31 to 1.34, and the tricyclic terpane content is low, which reflects that the sedimentary environment of crude oil is a brackish-saline reducing one with mainly algae source input. According to the study of oil source correlation, there are two sources of the low-mature oils from the Tengeer Formation (2^nd member) in the Saihantala Sag: (1) from the underlying Tengeer Formation (1^st member) source rock and hydrocarbon generation at the early mature stage in salt-water environment; (2) from the self-generation and self-storage of the lowly-mature Tengeer Formation (2^nd member) source rock in the depression center.

Key words: low-mature oil, geochemical characteristics, biomarker, oil-source correlation, Saihantala Sag, Erlian Basin

CLC Number:

TE122.1

LI Jiehao, HOU Dujie, CAO Lanzhu, WU Piao, ZHAO Zhe, MA Xiaoxiao. Geochemical Characteristics and Source Correlation of Low-mature Oil from the Tengeer Formation (2^nd Member) in the Saihantala Sag, Erlian Basin[J]. Geoscience, 2021, 35(02): 315-325.

Figures/Tables 13

Fig.1 Tectonic division of the Saihantala Sag and sampling well location

Table 1 Group compositions of crude oils and oil sandstone samples from the Tengeer Formation (2nd member) in the Saihantala Sag

井号	类型	深度/m	层位	饱和烃/%	芳烃/%	(非烃+沥青质)/%	饱/芳
赛84	原油	1 560~1 577.3	K₁bt₂	39.99	12.57	47.43	3.18
赛63-2x	原油	1 426.2~1 441.4	K₁bt₂	48.22	15.53	36.26	3.11
赛27	油砂	1 655.47	K₁bt₂	57.65	13.17	29.18	4.38
赛56	油砂	1 482.35	K₁bt₂	63.47	14.67	21.86	4.33
赛63	油砂	1 331.32	K₁bt₂	58.45	12.08	29.47	4.84
赛56	油砂	1 408	K₁bt₂	60.28	15.77	23.95	3.82
赛61	油砂	976.53	K₁bt₂	59.54	15.31	25.15	3.89

Table 2 Geochemical characteristics parameters of crude oil and oil sandstone samples from the Tengeer Formation (2nd member) in the Saihantala Sag

井号	类型	Pr/Ph	Pr/nC₁₇	Ph/nC₁₈	Ts/Tm	C₂₉甾烷 20S/(20S+20R)	C₂₉甾烷 ββ/(αα+ββ)	伽马蜡烷指数
赛84	原油	0.59	0.41	0.73	0.91	0.31	0.30	0.31
赛63-2x	原油	0.49	0.37	0.78	0.69	0.35	0.31	0.71
赛27	油砂	0.34	0.34	0.76	1.08	0.33	0.34	0.64
赛56	油砂	0.45	0.29	0.57	0.83	0.40	0.38	0.33
赛63	油砂	0.29	0.58	1.37	0.72	0.27	0.29	1.34
赛56	油砂	0.58	0.41	0.58	0.67	0.38	0.39	0.08
赛61	油砂	0.51	0.47	0.80	0.60	0.31	0.35	0.42

Fig.2 Gas chromatograms of saturated hydrocarbon of crude oil and oil sandstone samples from the Tengeer Formation (2nd member) in the Saihantala Sag

Fig.3 Isoprenoid hydrocarbon ratios diagram of crude oil and oil sandstone samples from the Tengeer Formation (2nd member) in the Saihantala Sag

Fig.4 Mass chromatograms of steranes and terpanes of crude oil and oil sandstone samples from the Tengeer Formation (2nd member) in the Saihantala Sag

Table 3 Geochemical characteristics of hydrocarbon source rocks in the Saihantala Sag

烃源岩层位	有机质类型	镜质组反射率R_o/%	Pr/Ph	Pr/nC₁₇	Ph/nC₁₈	C₂₉甾烷 20S/(20S+20R)	C₂₉甾烷 ββ/(αα+ββ)	伽马蜡烷指数
腾二段	Ⅱ₂—Ⅲ型	0.32~0.85(0.55)	0.29	0.26	0.45	0.02~0.43 (大多<0.25)	0.14~0.45 (大多<0.25)	0.16~3.14
腾一段	Ⅰ—Ⅱ₁型	0.38~1.11(0.66)	0.49	0.21	0.29	0.25~0.46	0.23~0.45	0.12~2.25
阿尔善组	Ⅱ₁—Ⅱ₂型	0.50~1.38(0.99)	0.54	0.22	0.24	0.35~0.55	0.31~0.51	0.22~1.2

Fig.5 Comparison of chromatogram and mass spectra of saturated hydrocarbon between well Sai 84 crude oil and well Sai 83, Sai 85x source rocks

Fig.6 Scatter diagram of correlation between well Sai 84 crude oil and wells Sai 83, Sai 85x source rocks

Fig.7 Comparison of chromatogram and mass spectra of saturated hydrocarbon between wells Sai 27 and Sai 63 oil sandstones and wells Sai 12 and Sai 97 source rocks

Fig.8 Scatter correlation diagrams for wells Sai 27 and Sai 63 oil sandstones and wells Sai 12 and Sai 97 source rocks

Fig.9 Comparison of chromatogram and mass spectra of saturated hydrocarbon between well Sai 56 oil sandstone and well Sai 85x source rock

Fig.10 Scatter correlation diagrams for wells Sai 56 and 61 oil sandstones and well Sai 85 source rocks

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