西非裂谷系Termit盆地古近系油气成藏主控因素分析

Termit盆地隶属于西非裂谷系，是发育于前寒武系-侏罗系基底之上的中、新生代裂谷盆地。国外石油公司自1974年开始对该盆地进行勘探，截止2008年在中国石油获得勘探许可前，仅在西部Dinga断阶带发现7个油气藏，区域甩开勘探没有获得商业发现。针对这一国外石油公司勘探近40年后放弃的区块，面临着如何寻找潜力区带、发现规模油气的巨大挑战。本文基于Termit盆地晚白垩世大规模海侵、早白垩世和古近纪两期裂谷叠置的构造演化特点，分析了古近系油气成藏的主控因素。这种后期叠置裂谷(古近纪)的成藏模式有别于其他纯陆相单一旋回的裂谷盆地，烃源岩为上白垩统海相泥页岩，储层为古近系陆相砂岩，盖层为古近系湖相泥岩，表现为跨世代(跨二级层序)油气聚集特征。其油气成藏具有6个主控因素，即大范围海相烃源岩“控源”、叠置裂谷“控砂”、断裂与砂岩输导层“控运”、构造地貌“控势”、断层与砂体配置“控藏”、盖层与侧向封挡“控保”。成藏主控因素分析揭示了Termit盆地古近系的油气富集规律，有效指导了该盆地潜力区带评价与规模油气发现。

Main controlling factors of Paleogene hydrocarbon accumulation of Termit Basin,West African rift system

The Termit Basin, which is located in the southeastern Niger and tectonically belongs to the northern part of West African Rift System (WARS), is a Mesozoic Cenozoic rift basin developed on the Precambrian Jurassic basement. Since 1974, many foreign oil companies have made exploration in Termit Basin and found seven reservoirs in Dinga Faulted Terrace. CNPC began exploration in the basin in 2008. It is a very difficult issue that how to evaluate the potential and find abundant petroleum. Based on the tectonic evolution of the Late Cretaceous great transgression and two rifts superimposition, this study mainly focuses on analyzing the main controlling factors of Paleogene hydrocarbon accumulation. The petroleum accumulation model of the Paleogene shows the following six characteristics: (1) hydrocarbon generation is controlled by the large area of marine source rocks; (2) sandstone distribution is influenced by superimposition of two phases rifting; (3) secondary migration of oil and gas is controlled by faults and thick carrier beds; (4) fluid potential is decided by structural relief; (5) petroleum accumulation is determined by the relationship between faults and sandstone; (6) preservation of oil and gas is defined by cap rocks and lateral blockages. The analysis of main controlling factors reveals the petroleum accumulation principles of the Paleogene, and facilitates the exploration of the Termit Basin.