东非共轭型大陆边缘油气成藏差异性分析

Differences in Petroleum Geological Conditions of Conjugate Continental Margin in East Africa

被动大陆边缘张裂形成过程中,在陆缘两侧很容易形成共轭型大陆边缘。大西洋两侧的西非和南美便是典型的例子,由于具有共轭的成因演化,因而具有相似的油气成藏条件。受此启示,推测东非大陆边缘也是在东西冈瓦纳大陆裂解背景下形成的,也应该发育类似大西洋共轭型大陆边缘。通过研究东非构造演化,东非海岸北段—孤岛区具备共轭型大陆边缘的特性,两侧均经历了早期裂谷和晚期被动陆缘的沉积和构造演化,油气地质条件十分相似,勘探成效也证实它们是东非大陆边缘油气最富集的区域。但共轭两侧油气类型差异较大,东非海岸北段以天然气为主,孤岛区则以稠油沥青为主,初步研究认为后期构造的改造和破坏作用直接导致了东非共轭型大陆边缘油气成藏的差异。

When passive continental margin extends to both sides, it is easy to form conjugate continental margin. On both sides of the Atlantic Ocean in the West Africa and South America is a typical example. Due to the conjugate evolution, continental margin usually has similar petroleum geological conditions. Based on this,East Africa continental margin,under the background of breakup of East and West Gondwana,should also be similar to the Atlantic conjugate type of continental margin. However,because of no consistent breakup time between the plates,the conjugate characteristics are not obvious and were not discussed in the past. By studying tectonic evolution in East Africa, the northern section of coastal East Africa and islands areas have features of conjugate type of continental margin. Both sides underwent the tectonic evolution of early rifting and late passive continental margin and have similar petroleum geological conditions. Exploration results have confirmed that they are the most enrichment of oil and gas regions in East Africa continental margin. However,conjugated hydrocarbon type has differences on both sides. The northern section of coastal East Africa is dominated by natural gas, while islands areas are mainly heavy oil or tar. Preliminary research suggests that the late period tectonic transformation and damage led directly to the differences among the conjugated hydrocarbon accumulation.