Types, characteristics, and implications on the exploration of far-source oil reservoirs in the north Melut Basin
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摘要: Melut盆地为非洲内陆一个重要含油气盆地，其北部具有下白垩统生油、古近系聚集成藏的远源成藏特征，明确盆地远源油藏形成条件与控制因素是提高远源油藏勘探成功率、寻找新的勘探领域的关键。基于区域石油地质条件与油藏解剖，开展了Melut盆地北部远源油藏形成条件、类型及特征研究，在此基础上提出了源内Yabus组远源断层-岩性复合油藏及源外Yabus组远源断块油藏两大潜力勘探领域。研究表明：Melut盆地北部古近系Yabus组发育源内和源外2种类型的远源油藏，二者具有不同的油气充注方式与成藏模式。源内Yabus组远源油藏的形成取决于3个地质条件的耦合，即"两强一弱"的3期裂陷作用为古近纪Yabus组-Adar组远源储盖组合的形成创造了条件；富油凹陷的发育为Yabus组远源油藏的形成提供了必要的油源基础；多期裂陷作用为Yabus组远源圈闭的油气充注提供了垂向通道条件。源内远源油藏主要通过油源断裂的垂向充注成藏，油源断裂是其成藏的主要控制因素，油源断裂的识别及控圈断层的侧向封堵性评价是源内远源断块圈闭评价的重点。源外远源油藏主要通过富油凹陷的侧向运移充注成藏，由富砂地层与断块、古隆起形成的输导脊控制源外远源圈闭的成藏，输导脊的识别与圈闭充注油气程度研究是源外远源圈闭评价的重点。研究成果指导了Melut盆地远源油藏的勘探部署与深化勘探，对其他含油气盆地成熟探区远源油藏的勘探具有指导和借鉴意义。Abstract: The Melut Basin is an important petroliferous basin in African Continent. The northern part of the basin is characterized by far-source oil accumulation with the oil generation in the Lower Cretaceous and the oil accumulation in the Paleogene. Clarifying the formation conditions and controlling factors of the far-source oil accumulations is the key to improve the exploration success rate and seek new potential areas of far-source oil accumulations in the Melut Basin. Based on the study of regional petroleum geological conditions and the analysis of key oil accumulations, the formation conditions, types, characteristics and potential exploration areas of far-source oil accumulations in the Melut Basin have been systematically studied. The results show, ①The north Melut Basin develops two types of far-source oil accumulations with different hydrocarbon charging patterns and accumulation modes in the Paleogene Yabus Formation, the far-source fault-lithology combination oil accumulations within the oil kitchen and the far-source fault-block oil accumulations outside the oil kitchen; ②The formation of far-source oil accumulations of the Yabus Formation inside oil kitchen depends on the coupling of three geological conditions, that is, the "two strong and one weak" three-stage rifting cycles, creating conditions for the formation of the Paleogene Yabus-Adar far-source reservoir-caprock combination; the development of oil-rich sag, providing necessary oil supply for the Yabus far-source traps; and the multi-stage rifting activities, providing vertical migration pathways for hydrocarbon charging in the Yabus far-source traps; ③The far-source oil accumulations inside oil kitchen are mainly charged by the vertical hydrocarbon infilling through the oil-source faults, and the oil-source faults are the main controlling factor for the hydrocarbon accumulation. The identification of oil-source faults and the evaluation of the lateral sealing capability of trap-controlling faults are the key elements for the far-source fault-block traps inside oil kitchen; ④The far-source oil accumulations outside oil kitchen are mainly charged by lateral hydrocarbon infilling from the oil-rich sag. The transportation ridges formed by sand-rich strata, fault blocks and paleo-uplifts control the hydrocarbon accumulation of far-source traps outside oil kitchen. The identification of transportation ridges and the study on the hydrocarbon charging extent are the main evaluation focus of far-source traps outside oil kitchen. The research results successfully guided the exploration deployment and in-depth exploration of far-source oil accumulations in the Melut Basin, and have a great implication on the exploration of far-source oil accumulations in the other petroliferous basins.
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Key words:
- Melut Basin /
- Paleogene /
- Yabus Formation /
- far-source oil accumulation /
- accumulation characteristics
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图 1 含油气盆地源内远源油藏、源外远源油藏及源内近源油藏分布示意图
源外远源油藏：①⑦；源内远源油藏：②⑥；源内近源油藏：③④⑤
Figure 1. Sketch of the far-source oil reservoirs inside and outside oil kitchen and near-source oil reservoirs inside oil kitchen in a petroliferous basin
图 2 中西非裂谷系(a)、Melut盆地地层综合柱状图(b)及Melut盆地构造单元(c)
Q.第四系; E.古近系; N.新近系; K2.上白垩统; K1.下白垩统
Figure 2. Central-West African Rift System (a), strata column (b) and structure unit (c) of the Melut Basin
图 3 Melut盆地北部拉张系数(a)及沉积充填与成藏模式(b)
Figure 3. Tension coefficient (a), sedimentary filling and hydrocarbon accumulation mode (b) of the north Melut Basin
图 4 北部凹陷Al Renk组烃源岩厚度图(a)及过凹陷中心二维剖面现今Ro等值线图(b)
Figure 4. Thickness map of Al Renk source rocks (a) and the Ro value of the section across basin center (b) of the Northern Sub-basin
图 5 北部凹陷断裂发育特征与油气运聚成藏模式(剖面位置见图 2-c)
Figure 5. Features of fault system and hydrocarbon accumulation mode of the Northern Sub-basin
图 6 Gumry油藏Yabus组上段均方根振幅属性(a)及砂岩透镜体地震剖面反射特征(b)
Figure 6. RMS attribute of the Upper Yabus Formation in the Gumry oil reservoir (a) and the reflection features of the sand lens in seismic profile (b)
图 7 Melut盆地北部凹陷远源油藏成藏模式图
Figure 7. Accumulation mode of the far-source oil reservoirs in the Northern Sub-basin, Melut Basin
图 8 北部凹陷Yabus组沉积相剖面(a)及Yabus组上段油层厚度(b)与日产量特征(c)
Figure 8. Sedimentary facies section of Yabus Formation (a), and the features of oil-layer thickness and daily production of the Upper Yabus Formation (c) in the Northern Sub-basin
图 9 Gasab油田Yabus组上段水下分流河道地震属性特征(A)、构造图(图中为高程(m)等值线) (B)及油藏剖面(C)
Figure 9. Seismic attribute(A), structure map (B) and oil reservoir section (C) of the subaqueous distributary channels in the Upper Yabus Formation, Gasab Oilfiled
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