Geochemical Characteristics and Source of Crude Oil in Chang 8 Member of Yanchang Formation, Ganquan Area, Ordos Basin

doi:10.19657/j.geoscience.1000-8527.2022.199

Abstract

Abstract:

Through systematic collection of crude oil, sandstone and source rock samples from Ganquan in the southeastern Ordos Basin, the geochemical characteristics of Chang 8 crude oil in Yanchang Formation were characterized, and the origin and source of the crude oil clarified. We show that Chang 8 crude oil is the normal crude oil featured by low viscosity, initial boiling point, pour point and sulfur content. The Chang 8 crude oil have mixed organic matter sources, which were formed in a weakly reducing environment during the peak oil generation stage. According to the distribution characteristics of C₃₀DiaH and dicyclic sesquiterpenes, the crude oils can be divided into type I and II: Type I crude oil is mainly distributed in Chang 8₁reservoir, and type II crude oil is distributed in Chang 8₂ reservoir. The Chang 9 and Chang 8 source rocks are featured by low C₂₄TeT/C₂₆TT, abnormally high C₃₀DiaH, high 8β(H)-homodrimane and 8β(H)-drimane, while Chang 7 source rock show the opposite features. Oil-source correlation shows that type I crude oil was sourced from Chang 7 source rock, whilst type II crude oil was sourced from Chang 8 and Chang 9 source rocks. The crude oils in Ganquan are mainly enriched in Chang 8₂ member, and Chang 8₂ reservoir in western Ganquan was contributed by Chang 8 and Chang 9 source rocks, while Chang 8₂ reservoir in eastern Ganquan was mainly contributed by Chang 9 (and minor Chang 7) source rocks. We recognize that the hydrocarbon contribution of the Chang 8 and Chang 9 source rocks may have been key to the crude oil enrichment in the Chang 8₂ member, which has guiding significance for future exploration.

Key words: Ordos Basin, Ganquan area, Chang 8 crude oil, geochemical characteristics of crude oil, oil source correlation

CLC Number:

TE122.1

ZHU Biqing, CHEN Shijia, BAI Yanjun, LEI Junjie, YIN Xiangdong. Geochemical Characteristics and Source of Crude Oil in Chang 8 Member of Yanchang Formation, Ganquan Area, Ordos Basin[J]. Geoscience, 2022, 36(02): 742-754.

Figures/Tables 13

Fig.1 Location of study area ((a) modified after ref.[25]) and distribution map of sampling wells (b) at Ganquan, Ordos Basin

Fig.2 Reservoir profile diagram(see Fig.1 for the section location)

Table 1 Physical properties of Chang 8 crude oil at Ganquan, Ordos Basin

井名	层位	密度/ (g/cm³)	黏度/ (mPa·s)	初馏点/ ℃	凝点/ ℃	含硫量/ %	原油性质
X49	长8₁	0.83	3.25	50	10	0.02	正常原油
X90	长8₁	0.83	4.27	100	24	0.01	正常原油
X53	长8₁	0.82	3.26	65	18	0.01	正常原油
LP193	长8₁	0.84	5.29	68	12	0.01	正常原油
LP168	长8₁	0.81	2.55	45	10	0.02	正常原油
LP184	长8₁	0.82	2.60	48	18	0.02	正常原油
LP184	长8₂	0.82	3.64	47	23	0.01	正常原油
LP18	长8₂	0.83	3.75	53	27	0.02	正常原油
X50	长8₂	0.83	3.00	58	20	0.02	正常原油
X67	长8₂	0.83	3.65	60	30	0.02	正常原油
Q20	长8₂	0.82	3.81	75	30	0.01	正常原油
LP205	长8₂	0.84	5.38	121	24	0.01	正常原油
X90	长8₂	0.83	3.80	120	20	0.01	正常原油
X53	长8₂	0.82	5.11	65	22	0.01	正常原油
LP193	长8₂	0.85	5.27	120	16	0.01	正常原油
LP168	长8₂	0.84	5.40	95	24	0.02	正常原油

Table 2 Gas chromatographic parameters of saturated hydrocarbons of crude oil, reservoir extracts and source rock samples at Ganquan, Ordos Basin

样品代号	深度/m	层位	井位	样品类型	主峰碳	OEP	CPI	∑n $C 21 -$ / ∑n $C 22 +$	(nC₂₁+nC₂₂)/ (nC₂₈+n $C 29)$	Pr/Ph	Pr/nC₁₇	Ph/nC₁₈
GQ1	/	长8₁	X130	原油	C₁₉	1.06	1.09	1.43	2.15	1.14	0.32	0.25
GQ2	1 564	长8₁	Q33	油砂	C₁₆	1.07	1.11	1.19	1.26	1.13	0.31	0.20
GQ3	1 353	长8₁	X129	油砂	C₂₁	1.06	1.05	0.65	1.39	1.07	0.39	0.30
GQ4	1 507	长8₂	X130	油砂	C₁₉	1.02	1.03	1.00	2.07	1.39	0.38	0.19
GQ5	/	长8₂	Q33	原油	C₁₉	1.06	1.10	1.32	1.89	1.47	0.32	0.18
GQ6	/	长8₂	Q23	原油	C₁₅	1.02	1.03	1.60	2.32	1.50	0.27	0.17
GQ7	1 478	长8₂	X108	油砂	C₁₉	1.04	1.08	1.38	3.03	1.64	0.15	0.11
GQ8	1 481	长8₂	X108	油砂	C₁₉	1.02	1.05	0.94	2.16	1.42	0.26	0.17
GQ9	1 415	长8₂	X129	油砂	C₂₁	1.04	1.04	0.68	1.62	1.20	0.73	0.48
GQ10	1 417	长7	Q37	烃源岩	C₁₉	1.08	1.11	1.02	2.24	1.16	0.27	0.22
GQ11	1 277	长7	X129	烃源岩	C₁₉	1.06	1.15	1.02	1.31	1.18	0.73	0.58
GQ12	1 574	长8	Q20	烃源岩	C₁₄	1.05	1.12	1.57	2.47	1.15	0.20	0.16
GQ13	1 638	长8	Q33	烃源岩	C₁₅	1.01	1.03	1.40	2.05	1.32	0.21	0.16
GQ14	1 456	长9	X126	烃源岩	C₁₅	1.00	1.02	2.10	3.06	1.35	0.16	0.13
GQ15	1 508	长9	Q7	烃源岩	C₁₇	1.02	1.02	1.63	2.60	1.63	0.23	0.14

Table 2 Gas chromatographic parameters of saturated hydrocarbons of crude oil, reservoir extracts and source rock samples at Ganquan, Ordos Basin

样品代号	深度/m	层位	井位	样品类型	主峰碳	OEP	CPI	∑n $C 21 -$ / ∑n $C 22 +$	(nC₂₁+nC₂₂)/ (nC₂₈+n $C 29)$	Pr/Ph	Pr/nC₁₇	Ph/nC₁₈
GQ1	/	长8₁	X130	原油	C₁₉	1.06	1.09	1.43	2.15	1.14	0.32	0.25
GQ2	1 564	长8₁	Q33	油砂	C₁₆	1.07	1.11	1.19	1.26	1.13	0.31	0.20
GQ3	1 353	长8₁	X129	油砂	C₂₁	1.06	1.05	0.65	1.39	1.07	0.39	0.30
GQ4	1 507	长8₂	X130	油砂	C₁₉	1.02	1.03	1.00	2.07	1.39	0.38	0.19
GQ5	/	长8₂	Q33	原油	C₁₉	1.06	1.10	1.32	1.89	1.47	0.32	0.18
GQ6	/	长8₂	Q23	原油	C₁₅	1.02	1.03	1.60	2.32	1.50	0.27	0.17
GQ7	1 478	长8₂	X108	油砂	C₁₉	1.04	1.08	1.38	3.03	1.64	0.15	0.11
GQ8	1 481	长8₂	X108	油砂	C₁₉	1.02	1.05	0.94	2.16	1.42	0.26	0.17
GQ9	1 415	长8₂	X129	油砂	C₂₁	1.04	1.04	0.68	1.62	1.20	0.73	0.48
GQ10	1 417	长7	Q37	烃源岩	C₁₉	1.08	1.11	1.02	2.24	1.16	0.27	0.22
GQ11	1 277	长7	X129	烃源岩	C₁₉	1.06	1.15	1.02	1.31	1.18	0.73	0.58
GQ12	1 574	长8	Q20	烃源岩	C₁₄	1.05	1.12	1.57	2.47	1.15	0.20	0.16
GQ13	1 638	长8	Q33	烃源岩	C₁₅	1.01	1.03	1.40	2.05	1.32	0.21	0.16
GQ14	1 456	长9	X126	烃源岩	C₁₅	1.00	1.02	2.10	3.06	1.35	0.16	0.13
GQ15	1 508	长9	Q7	烃源岩	C₁₇	1.02	1.02	1.63	2.60	1.63	0.23	0.14

Table 3 Characteristics of steranes and terpenes of source rock and Chang 8 crude oil at Ganquan, Ordos Basin

样品代号	规则甾烷相对含量			A	B	C	D	E	F	G	H	R_o/%
样品代号	C₂₇	C₂₈	C₂₉	A	B	C	D	E	F	G	H	R_o/%
GQ1	0.30	0.29	0.41	0.73	0.69	0.63	0.48	0.47	14.73	1.49	0.52	1.18
GQ2	0.29	0.29	0.42	0.69	0.70	0.53	0.45	0.49	6.96	1.45	0.29	0.89
GQ3	0.29	0.30	0.40	0.73	0.76	0.57	0.56	0.39	5.10	0.84	1.24	0.97
GQ4	0.31	0.26	0.43	0.73	0.59	0.64	0.50	0.66	18.89	1.83	4.20	1.20
GQ5	0.37	0.26	0.37	0.99	0.68	0.62	0.55	0.27	5.74	3.28	3.32	1.12
GQ6	0.32	0.23	0.46	0.70	0.49	0.55	0.49	0.34	9.58	2.00	0.65	0.93
GQ7	0.37	0.27	0.35	1.07	0.78	0.51	0.49	0.26	1.93	6.80	1.42	0.85
GQ8	0.31	0.27	0.42	0.74	0.66	0.63	0.52	0.35	8.50	2.91	6.45	1.17
GQ9	0.31	0.27	0.42	0.73	0.64	0.62	0.51	0.39	9.30	1.84	4.94	1.14
GQ10	0.25	0.29	0.45	0.55	0.65	0.63	0.49	0.56	14.61	1.30	0.72	1.18
GQ11	0.30	0.27	0.43	0.69	0.61	0.62	0.49	0.86	18.66	2.02	0.68	1.15
GQ12	0.35	0.25	0.41	0.85	0.60	0.62	0.51	0.29	8.69	6.21	5.31	1.12
GQ13	0.39	0.26	0.36	1.09	0.72	0.55	0.52	0.27	6.26	4.68	5.25	0.94
GQ14	0.38	0.27	0.35	1.09	0.79	0.46	0.54	0.46	3.58	8.77	1.81	0.75
GQ15	0.33	0.30	0.37	0.90	0.81	0.59	0.55	0.46	4.04	5.43	1.80	1.02

Fig.3 Gas chromatogram of saturated hydrocarbons of source rocks and Chang 8 crude oil at Ganquan

Fig.4 Correlation between Pr/nC17 and Ph/nC18 of source rocks and Chang 8 crude oil at Ganquan

Fig.5 Mass chromatograms (m/z 217) of steroid from source rocks and Chang 8 crude oil at Ganquan

Fig.6 Distribution characteristics of steroids in source rocks, and Chang 8 crude oil at Ganquan, Ordos Basin

Table 4 Compound name of mass spectrum

峰号	化合物	化学式	名称来源
1	4,4,8,10-四甲基十氢化萘	C₁₄H₂₆	据文献[42]
2	C₁₄-倍半萜烷	C₁₄H₂₆	据文献[42]
3	C₁₅-新倍半萜烷	C₁₅H₂₈	据文献[49]
4	4,4,8,8,9-五甲基十氢化萘 (重排补身烷)	C₁₅H₂₈	据文献[42]
5	4,4,8,9,10-五甲基十氢化萘 (重排补身烷)	C₁₅H₂₈	据文献[46]
6	4,4,8,8,10-五甲基十氢化萘 (重排补身烷)	C₁₅H₂₈	据文献[46]
7	4,4,8,9,9-五甲基十氢化萘 (重排补身烷)	C₁₅H₂₈	据文献[42]
8	8β(H)-补身烷	C₁₅H₂₈
9	4,4,9,9,10-五甲基十氢化萘	C₁₅H₂₈
10	8α(H)-补身烷	C₁₆H₃₀
11	4,4,8,10-四甲基-9-乙基 -十氢化萘	C₁₆H₃₀	据文献[46]
12	4,4,8,9-四甲基-8-乙基 -十氢化萘	C₁₆H₃₀	据文献[46]
13	8β(H)-升补身烷	C₁₆H₃₀	据文献[42]

Fig.7 Mass chromatograms (m/z 191 and m/z 123) of terpenoid from source rocks and Chang 8 crude oil at Ganquan

Fig.8 Classification of crude oil types in Chang 8 member at Ganquan, Ordos Basin

Fig.9 Cluster analysis of source rocks and Chang 8 crude oil at Ganquan

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