平凉北地区长8段油藏油源及其成藏模式

doi:10.7657/XJPG20250308

摘要/Abstract

摘要：

为确定鄂尔多斯盆地平凉北地区延长组长8段油藏油源和成藏机理，综合应用饱和烃色谱、饱和烃色谱-质谱、碳同位素组成等，对研究区长8段原油有机地球化学特征和油源进行分析。研究区长8段原油密度和黏度差异较大，长8段原油遭受生物降解，具有较高的密度、黏度、Pr/nC₁₇和Ph/nC₁₈，重排藿烷类化合物相对丰度较低，ααα-20R甾烷呈不对称“V”字形分布，原油中C₂₇规则甾烷含量较高，原油母质以水生生物为主，形成于淡水—微咸水、弱氧化—弱还原沉积环境。平凉—郭塬地区长8段原油属于低成熟—成熟原油，Ts/Tm、三环萜烷/17α（H）、21β（H）藿烷值低于殷家城地区长8段原油，研究区长7段烃源岩有机质丰度、成熟度和发育规模均低于庆阳地区长7段，三环萜烷/17α（H），21β（H）藿烷值存在差异。对比原油与烃源岩的生物标志化合物特征，结合烃源岩发育特征及成熟度匹配关系，认为平凉—郭塬地区长8段原油与平凉北地区长7段烃源岩匹配较好，原油以垂向运移成藏为主；殷家城地区长8段原油与庆阳地区长7段烃源岩匹配较好，原油以侧向输导运移成藏为主。

关键词: 鄂尔多斯盆地, 天环坳陷, 西缘冲断带, 延长组, 长8段, 油源, 成藏机理

Abstract:

To determine the oil source and hydrocarbon accumulation mechanism for the eighth member of the Yanchang formation (Chang 8 member) in the northern Pingliang area of the Ordos Basin, chromatography and chromatography-mass spectrometry of saturated hydrocarbon, and carbon isotope composition were combined to analyze organic geochemical properties and sources of the crude oil in the Chang 8 member. It is found that the crude oil in the Chang 8 member varies greatly in density and viscosity. Due to biodegradation, the crude oil in the Chang 8 member is characterized by high density, high viscosity, elevated Pr/nC₁₇ and Ph/nC₁₈ ratios, and relatively low abundance of rearranged hopanes. The ααα-20R steranes display an asymmetric V-shaped distribution, and the crude oil contains a high proportion of C₂₇ regular steranes, indicating that its organic precursor is primarily derived from aquatic organisms deposited in a freshwater to brackish water, weakly oxic to weakly reducing environment. The crude oil in the Chang 8 member in the Pingliang-Guoyuan area is classified as low mature to mature oil, with lower Ts/Tm, tricyclic terpane/17α(H), and 21β(H) hopane values compared to the crude oil in the Change 8 member in the Yinjiacheng area. The Chang 7 source rock in the study area has lower organic matter abundance, maturity, and development scale than those in the Qingyang area, with differences in tricyclic terpane/17α(H), and 21β(H) hopane values. By comparing the biomarkers of crude oil and source rocks, and considering the development and maturity of the source rocks, it is inferred that the crude oil in the Chang 8 member in the Pingliang-Guoyuan area is well correlated with the Chang 7 source rock in the northern Pingliang area, and it is mainly accumulated after vertical migration. In contrast, the crude oil in the Chang 8 member in the Yinjiacheng area is correlated with the Chang 7 source rock in the Qingyang area, and it is mainly accumulated after lateral transportation and migration.

Key words: Ordos Basin, Tianhuan depression, Western Margin thrust belt, Yanchang formation, Chang 8 member, oil source, accumulation mechanism

中图分类号:

TE122.1

罗丽荣, 李剑锋, 朱静, 孔令印, 白嫦娥, 居迎军, 侯云超. 平凉北地区长8段油藏油源及其成藏模式[J]. 新疆石油地质, 2025, 46(3): 318-328.

LUO Lirong, LI Jianfeng, ZHU Jing, KONG Lingyin, BAI Chang’e, JU Yingjun, HOU Yunchao. Oil Source and Hydrocarbon Accumulation Model of Chang 8 Reservoir in Northern Pingliang Area, Ordos Basin[J]. Xinjiang Petroleum Geology, 2025, 46(3): 318-328.

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地区	井名	密度/（g·cm^-3）	黏度/（mPa·s）	饱和烃含量/%	芳香烃含量/%	非烃含量/%	沥青质含量/%	饱和烃/芳香烃
殷家城地区	A5井	0.803 2	3.935	72.97	16.85	4.68	1.35	4.33
殷家城地区	A7井	0.832 5	4.249	68.65	14.74	4.17	1.69	4.66
彭阳地区	B1井	0.849 5	5.160	67.59	18.15	5.74	1.30	3.72
彭阳地区	C5井	0.813 6	2.375	70.22	18.00	4.92	2.04	3.90
平凉— 郭塬地区	C77井	0.888 6	20.223	58.84	21.92	5.95	5.71	2.68
	C20井	0.894 9	20.114	59.80	17.65	6.53	4.27	3.39
	C22井	0.898 2	24.487	59.54	17.92	19.65	4.62	3.32
	C10井	0.873 0	8.116	51.96	22.47	7.22	3.92	3.11
	C67井	0.869 7	10.692	62.38	19.31	17.82	3.96	3.23
	D13井	0.880 9	9.759	61.28	21.31	6.41	4.68	2.88
	D6井	0.833 3	9.099	52.45	12.25	17.65	17.65	4.28

原油类型	井名	Pr/Ph	Pr/nC₁₇	Ph/nC₁₈	OEP	CPI	C21^-/C 21⁺
正常原油	A7井	1.44	0.32	0.24	1.08	1.14	3.32
	C34井	1.13	0.32	0.30	1.22	1.12	1.65
	C39井	1.16	0.33	0.30	1.17	1.10	1.81
	C40井	1.13	0.32	0.30	1.16	1.09	1.90
	B1井	1.21	0.28	0.25	1.05	1.23	2.40
	C10井	1.41	0.34	0.25	1.08	1.18	2.30
	D13井	1.22	0.34	0.28	1.06	1.17	1.23
	D6井	1.30	0.33	0.26	1.12	1.05	1.82
生物降解原油	C20井	1.00	15.38	10.00	1.61	0.62	1.27
	C22井	1.21	1.08	0.91	1.06	1.31	2.03
	C77井	1.20	0.63	0.57	1.12	1.25	1.30