东非转换-伸展型被动陆缘盆地油气地质特征

Petroleum Geological Characteristics of Transformation-extensional Continental Margin Basins in East Africa

范玉海 屈红军 朱楠

FANYuhai QUHongjun ZHUNan

榆林学院, 陕西 榆林 719000 中国煤炭地质总局航测遥感局, 陕西 西安 710199 榆林通达铭泰地质科技有限公司, 陕西 榆林 719000 西北大学地质学系, 陕西 西安 710069

Yulin University, Yulin, Shaanxi 719000, China Aerial Survey and Remote Sensing Bureau of China Coal Geology Administration, Xi'an, Shaanxi 710199, China Yulin Tongda Mingtai Geological Technology Co. Ltd., Yulin, Shaanxi 719000, China Department of Geology, Northwest University, Xi'an, Shaanxi 710069, China

近年来，东非转换—伸展型被动陆缘深水区的鲁武马盆地和坦桑尼亚盆地发现了一系列大气田，可采储量达3.8$\times$10$^{12}$m$^3$，但该区资源发现率仅为13.1%，待发现资源潜力巨大，为此，在综合东非被动陆缘盆地研究成果的基础上，对区内烃源岩、储层、圈闭及运移等地质条件进行总结，并探讨了生储盖组合规律。结果表明：1)东非转换-伸展型陆缘盆地主力烃源岩以中上侏罗统—白垩系潟湖相、局限海相页岩或灰岩为主；主力储集层为中上侏罗统—白垩系—新近系海相碎屑岩。2)油气沿断层做“垂向式充注”或“横向式充注”，沿不整合面或储层做“测注式充注”；受控于东非复杂构造演化作用，形成了以构造、地层岩性为主的圈闭类型。3)成藏条件以鲁伍马、坦桑尼亚盆地最为优越，有利勘探层位为白垩系—新近系的砂岩储层；索马里盆地三叠系Calub组砂岩具有较好勘探前景。随着勘探程度和技术水平的提高，其他盆地油气勘探有望取得重大突破。

In recent years, a series of large gas fields have been discovered in the deepwater areas of the Rovuma Basin and Tanzania Basin on the transform-extensional passive continental margin of East Africa, with recoverable reserves reaching 3.8$\times$10$^{12}$ m$^3$. However, the resource discovery rate in this region is merely 13.1%, indicating a vast potential for undiscovered resources. Based on the comprehensive research achievements of passive continental margin basins in East Africa, this paper summarizes the geological conditions such as source rocks, reservoirs, traps, and migration within the area, and explores the combination patterns of source-reservoir-cap rocks. The results reveal that: 1) The main source rocks in the transform-extensional passive continental margin basins of East Africa are mainly the lagoon facies and restricted marine shale or limestone of the Middle-Upper Jurassic-Cretaceous & the main reservoir rocks are the marine clastic rocks of the Middle-Upper Jurassic-Cretaceous-Neogene. 2) Hydrocarbons are charged into the reservoirs through "vertical charging" or "lateral charging" along faults, and "lateral charging" along unconformities or reservoirs; controlled by the complex tectonic evolution of East Africa, trap types dominated by structures and stratigraphic lithologies have formed. 3) The conditions for hydrocarbon accumulation are most favorable in the Rovuma and Tanzania basins, and the favorable exploration horizons are the sandstone reservoirs of the Cretaceous-Neogene. The Triassic Calub Formation sandstone in the Somali Basin holds promising exploration prospects. With the advancement of exploration degrees and technical levels, significant breakthroughs are expected in the oil and gas exploration of other basins.

10.11885/j.issn.1674-5086.2024.08.29.01