南大西洋下刚果盆地烃源岩特征与成藏贡献

doi:10.19657/j.geoscience.1000-8527.2023.064

摘要/Abstract

摘要：

下刚果盆地位于南大西洋的非洲沿岸,由中生代裂谷盆地与新生代被动陆缘盆地叠合而成,是以岩盐构造发育为特色的富油气盆地。本文以二维地震、测井与地球化学资料为基础,结合前人勘探与研究成果,明确了该盆地烃源岩的类型与沉积环境,并通过烃源岩的热演化模拟、典型油气藏解剖、油气藏时空分布特征分析,揭示烃源岩发育特征及其在油气成藏中的贡献。研究表明,下刚果盆地在岩盐层之下的Bucomazi组发育湖相烃源岩,在岩盐层系之上的Iabe组、Landana组发育海相烃源岩。湖相烃源岩发育于干燥偏还原的湖盆环境中,有机质含量高;海相烃源岩发育于半深海-深海环境,累计厚度较大。在中新世后,Bucomazi组烃源岩进入生气阶段,Iabe组烃源岩进入生油阶段,为区内提供主要的油气供应。下刚果盆地油气藏类型及分布受烃源岩、断裂与盐构造等多重因素的影响,其中烃源岩的成熟、分布是关键要素。盐下油气藏多由近岸湖相烃源岩晚期供藏形成,而盐上油气藏则由多套烃源岩的多期供烃形成。

关键词: 下刚果盆地, 盐岩, 烃源岩, 热演化模拟, 成藏特征

Abstract:

The Lower Congo Basin, located along the African coast of the South Atlantic, is a petroliferous basin characterized by the salt tectonic development, which is composed of the Mesozoic rift basin and the Cenozoic passive continental margin basin.Based on two-dimensional seismic, well logging and geochemical data, combined with previous exploration and research results, we defined the types and sedimentary environments of source rocks in this basin, and clarified the source rock development characteristics and revealed their contributions to hydrocarbon accumulation.The study was conducted through thermal evolution simulation of source rocks, anatomy of typical hydrocarbon reservoirs, and analysis of the temporal-spatial distribution characteristics of hydrocarbon reservoirs.The results show that lacustrine source rocks are developed in the Bucomazi Formation under the salt layer, and marine source rocks are developed in the Iabe and Landana Formations above the salt layer.Lacustrine source rocks are developed in dry and reducing lacustrine basin environment with high organic matter content.Marine source rocks have large cumulative thickness, and developed in (semi-)abyssal environment.After the Miocene, the Bucomazi Formation source rocks entered the gas generation stage, and the Iabe Formation source rocks entered the oil generation stage, providing the main hydrocarbons in the region.The type and distribution of hydrocarbon reservoirs in the Lower Congo Basin are affected by multiple factors, such as the source rocks, faults and salt tectonics, among which the maturity and distribution of source rocks are the key ones.The subsalt oil and gas reservoirs are mostly formed by the late supply of lacustrine source rocks near the shore, while the soil and gas reservoirs above the salt were formed by the multi-stage supply of hydrocarbon from multiple source rocks.

Key words: Lower Congo Basin, salt rock, source rock, thermal evolution simulation, accumulation charac-teristics

中图分类号:

P618.13

杨雄兵, 王宏语, 苏玉山, 关超. 南大西洋下刚果盆地烃源岩特征与成藏贡献[J]. 现代地质, 2023, 37(05): 1369-1384.

YANG Xiongbing, WANG Hongyu, SU Yushan, GUAN Chao. Source Rock Characteristics and Its Accumulation Contribution in the Lower Congo Basin, South Atlantic[J]. Geoscience, 2023, 37(05): 1369-1384.

图/表 14

图1 下刚果盆地区域位置与主要断裂分布(据IHS数据库)

Fig.1 Regional location and major faults distribution of the Lower Congo Basin from IHS database

图2 下刚果盆地综合地层柱状图[27-28]

Fig.2 Comprehensive stratigraphic column of the Lower Congo Basin [27-28]

图3 下刚果盆地构造演化模式(剖面位置见图1的A-A’测线) (Ⅰ)盐下断陷层沉积末期;(II)盐下坳陷层沉积末期;(Ⅲ)过渡期末期;(Ⅳ)中中新统沉积末期;(Ⅴ)现今

Fig.3 Tectonic evolution model of Lower Congo Basin (seeing A-A’ in Fig.1 for location)

图4 非洲板块与南美洲板块分离过程中的气候特征[40] (a)前裂谷阶段,晚侏罗世;(b)同裂谷阶段,早白垩世;(c)过渡阶段,阿普特时期;(d)漂移阶段,白垩纪晚期

Fig.4 Climate conditions in the separation of African and South American plates [40]

图5 南大西洋中段区域各时期的沉积特征[41] (a)巴雷姆时期;(b)阿尔布时期;(c)土伦时期;(d)中新世时期

Fig.5 Sedimentary characteristics of each period in the central region of South Atlantic[41]

表1 下刚果盆地有利烃源岩的地球化学特征统计[34]

Table 1 Geochemical characteristics of main source rocks in the Lower Congo Basin [34]

深度(m)	层位	总有机碳 TOC(%)	生烃潜力 S₂(mg/g)	氢指数	氧指数	T_max均值 (℃)	生烃指数 (S₁/S₁+S₂)
1200	Lanada	1.5~2.4	1.8~6.8	100~235	23~118	429	0.03~0.06
1400	Lanada	1.4~2.2	2.4~5.0	116~199	30~48	430	0.04~0.08
1600	Lanada	1.6~2.2	2.5~8.2	122~303	21~55	428	0.05~0.07
1800	Iabe	3.4~5.0	39.3~46.5	>400	8~30	424	0.03~0.05
2000	Iabe	3.2~4.8	13.2~28.8	343~513	23~38	427	0.03~0.05
2200	Iabe	2.1~3.9	7.5~21.4	275~432	33~51	433	0.05~0.10
2300	Iabe	2.0~2.8	6.0~15.3	253~378	33~48	435	0.04~0.11
2400	Bucomazi	0.8~1.8	2.7~9.8	277~428	57~108	430	0.10~0.12
2500	Bucomazi	1.2~2.8	7.5~17.2	>480	42~94	431	0.09~0.12
2600
2800	Bucomazi	3.2~4.8	>12.3	>400	48~105	433	0.09~0.11
3000
3200	Bucomazi	1.3~2.7	4.2~10	317~482	62~103	436	0.09~0.17
3400	Bucomazi	1.5~4.1	5~13.1	126~285	30~76	445	0.05~0.09
3600	Bucomazi	2.0~4.1	2.5~10	131~320	38~101	441	0.05~0.10
3800

图6 下刚果盆地烃源岩氢指数(HI)与热解峰值(Tmax)交会图[42]

Fig.6 Intersection diagram of hydrogen index (HI) and pyro-lysis temperature peak (Tmax) of source rocks in the Lower Congo Basin [42]

图7 下刚果盆地陆域与海域深度-地温交汇图

Fig.7 Depth vs.geothermal intersection diagram of land and sea area in the Lower Congo Basin

图8 下刚果盆地北部热演化剖面(剖面位置见图1的B-B’ 测线) (Ⅰ)上白垩统沉积末期;(II)渐新统沉积末期;(Ⅲ)中中新统沉积末期;(Ⅳ)现今

Fig.8 Thermal evolution profile of the northern Lower Congo Basin (seeing B-B’ in Fig.1 for location)

图9 下刚果盆地南部热演化剖面(剖面位置见图1的C-C’测线) (Ⅰ)上白垩统沉积末期;(II)渐新统沉积末期;(Ⅲ)中中新统沉积末期;(Ⅳ)现今

Fig.9 Thermal evolution profile of the southern Lower Congo Basin (seeing C-C’ in Fig.1 for location)

图10 下刚果盆地主力烃源岩在现今阶段的成熟度分布 (a) Bucomazi组烃源岩;(b)Iabe组烃源岩;(c)Landana组烃源岩

Fig.10 Maturity distribution of main source rocks in the Lower Congo Basin at present

图11 下刚果盆地油气藏平面分布特征[41]

Fig.11 Plane distribution characteristics of oil and gas reservoirs in the Lower Congo Basin [41]

图12 研究区现今各主力油气藏的 “源-藏”配置关系示意 (a)近岸盐下油气藏; (b)Takula油气藏; (C)Gardenia油气藏; (d)Agogo油气藏

Fig.12 “Source rock and reservoir" combination relationship of the main reservoirs in the study area

图13 下刚果盆地油气成藏模式

Fig.13 Hydrocarbon accumulation model of the Lower Congo Basin

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