Passive continental margin basin evolution of East Africa and the main controlling factors of giant gas fields: an example from the Rovuma Basin

Many giant gas fields, concentrated in the Rovuma Basin of the East Africa passive margin basins, were discovered in recent years with a total recoverable reserves up to 3.8 trillion cubic meters. The Rovuma Basin has gone through three stages of tectonic evolution, i.e. the Karoo rift, Madagascar rift and Madagascar drift. The Lower-Middle Jurassic lacustrine and shallow sea source rocks formed in the Madagascar rift period, and came to the oil window, the peak of oil generation and the gas window, in the Early Cretaceous, the Late Cretaceous and the Oligocene, respectively. Affected by the East Africa onshore faults during the Madagascar drift period, massive sand-rich sediments accumulated towards the deep water region by way of block transport and deep water sliding. It formed a super giant deep-water-gravity-flow sandbody, wide and thick, with relatively uniform lithology and favorable physical property within the basin. The marine mudstone during the Madagascar drift period provided a good regional overlying strata. The early uplift onshore East Africa and delta progradation led to the formation of gravity sliding and salt diapir within the Rovuma Basin, and subsequently the East Africa normal fault zone (EANFZ) and the East Africa thrust fault zone (EATFZ), between the Oligocene and Pliocene. As a result, hydrocarbons from the underlying Lower-Middle Jurassic source rocks migrated upward along the normal and deep water thrust faults, accumulating in the structural-lithological-stratigraphy and structural traps to form the giant gas fields. © 2018, Editorial Office of Earth Science Frontiers. All right reserved.