尼日尔Termit盆地油气成藏新认识与勘探方向

New understanding and exploration direction of hydrocarbon accumulation in Termit Basin,Niger

基于地震、钻井、铸体薄片、油样和岩样地球化学分析、生烃史模拟等资料,研究尼日尔Termit海陆相叠合盆地油气成藏特征,并探讨未来油气勘探方向。研究认为:(1)Termit盆地为早白垩世和古近纪两期裂谷叠合,东部Trakes斜坡2口钻井沉降曲线显示晚白垩世沉降速率高,分析认为是遭受海侵影响造成的高沉积速率,也可能存在一期弱裂谷发育;(2)Termit盆地沉积层序主要受控于晚白垩世海侵期旋回和古近纪湖侵期旋回控制,发育海-陆“两种源汇”沉积叠合,海侵期广覆式发育的海陆相混源型烃源岩全盆地分布,湖侵期形成的古近系Sokor 1组储集层和Sokor 2组盖层叠置其上,形成了中西非裂谷系独特的海陆相裂谷叠合盆地;(3)Termit盆地早期地温梯度低,盆地主力烃源岩上白垩统Yogou组在古近纪晚期生烃。Trakes斜坡发育上白垩统Donga组成熟烃源岩,为“双源”供烃油气成藏模式,形成Trakes斜坡油田群;(4)Termit盆地海陆相裂谷叠合成藏模式新认识和勘探实践,扩大了盆地东部有效勘探面积约2500 km2,认为在盆地东南新区带Sokor 1组、新层系Donga组和上白垩统岩性目标具备勘探潜力,可作为未来勘探和选区重点。

Based on the seismic and drilling data,casting thin sections,geochemical analysis of oil and rock samples,and hydrocarbon generation history simulation,the hydrocarbon accumulation characteristics and exploration direction of Termit superimposed marine–continental rift basin are discussed.The Termit basin is superimposed with two-phase rifts(Early Cretaceous and Paleogene).The subsidence curves of two wells on the Trakes slope in the east of the basin show high subsidence rate in the Late Cretaceous,which is believed to be high deposition rate influenced by transgression.However,there may also be a weak rift development.The depositional sequences in the Termit basin were controlled by the Late Cretaceous marine transgression cycle and the Paleogene lacustrine transgression cycle,giving rise to two types of superimposed marine–continental“source-sink”deposits.The marine and continental mixed source rocks developed universally in the marine transgression period cover the whole basin,and are overlaid by the Paleogene Sokor 1 reservoir rocks and Sokor 2 caprocks developed in the lacustrine transgression period,forming the unique superimposed marine–continental basin in WCARS.The early low geothermal gradient of the Termit basin resulted in the late hydrocarbon generation in Paleogene of the Upper Cretaceous Yogou source rocks.Mature Upper Cretaceous Donga source rocks developed in the Trakes slope,and the double-source hydrocarbon accumulation model is proposed for the Trakes slope,which formed the oil fields in the Trakes slope.By virtue of the newly proposed hydrocarbon accumulation model for the Termit superimposed marine–continental rift basin and the exploration activities,an additional effective exploration area of about 2500 km~2 has been confirmed in the east of the basin.It is believed that Sokor 1,Donga and Upper Cretaceous lithologic traps in the southeast of the basin have exploration potentials,and they are key expected targets for future exploration and frontier evaluation.