Exploration targets in the Côte d'Ivoire-Ghana transform margin in Equatorial West Africa

Abstract

The Côte d'Ivoire-Ghana transform margin is a typical transform margin in the world. Extended margins (e.g. Abidjan-Cape Three Points and Accra-Benin segments) and transform margins (e.g. Cape Three Points-Accra segment) are present in this margin which have different evolution histories and structures. Along the Romanche Transform Fault was formed the high-uplifted Côte d'Ivoire-Ghana Margin Ridge. The transform margin experienced pre-transform, syn-transform and post-transform stages, and structures in different stages controlled their respective styles and sediments. In the Abidjan and Benin basins, the shelves are narrower and the slopes wider, obvious depocenters are formed with thick marine, non-marine and turbidity current sediments in the pre-transform and syn-transform stages, and the maturity of hydrocarbon sources is higher. In the Ghana Platform margin, the shelf is wider and the slope steeper, there isn't any obvious depocenter. The sediment load in this margin is small, and the maturity of hydrocarbon sources (even the Palaeozoic source) is low. The bathyal and deep sea in the Abidjan and Benin basins is the most attractive area for hydrocarbon exploration. But the exploration in the Ghana platform margin should focus on Palaeozoic to Early Cretaceous reservoirs. 摘要: 科特迪瓦—加纳转换边缘是世界上典型的转换型边缘, 沿边缘不同区段形成了伸展型边缘 (阿比让—三尖角区段和阿克拉—贝宁区段)和转换型边缘 (三尖角—阿克拉区段), 表现为不同的边缘形态、结构、构造特征, 沿罗曼彻转换断层形成了隆升很高的科特迪瓦—加纳边缘脊。转换边缘经历了前转换、同转换和后转换阶段等, 不同构造阶段控制了不同构造样式和沉积特征。阿比让盆地和贝宁盆地边缘的陆架较窄、斜坡很宽、盆地范围较广, 发育比较明显的沉积中心, 沉积了前转换阶段、同转换阶段海相、非海相和浊流沉积, 烃源岩成熟度高, 而加纳台地区边缘陆架较宽、斜坡陡峻, 没有发育明显的沉积中心, 沉积负载较小, 古生代泥盆系烃源岩也只部分成熟。据沉积分布、构造特征及烃源岩成熟度等方面综合分析, 阿比让盆地和贝宁盆地的半深水—深水区为最佳勘探前景地区, 加纳台地区应当重视古生代—早白垩世早期的油气藏。 Key words: extended margin, transform margin, petroleum geology, exploration target, Côte d'Ivoire-Ghana transform margin