Deep-water Natural Gas Differential Migration and Enrichment in East African Transform Continental Marginal Basins

Compared to discrete continental marginal basins, the mechanisms of hydrocarbon migration and enrichment in transform continental marginal basins are poorly understood. In this study, we conducted a comprehensive analysis of the main source rocks, reservoirs, and vertical migration pathways within the Rovuma (RB) and Tanzania (TB) basins in East Africa utilizing drilling, logging, seismic, and geochemical data. The results indicate that the enhanced preservation conditions of the Lower Jurassic source rocks in the southwest could lead to the discovery of large natural gas fields in the southern TB and RB. The primary reservoir is a deep-water turbidite sandstone. Due to topographic differences, the expanse of the turbidite sandstones in the RB is significantly larger than those in Tanzania. The main vertical migration pathways are the western boundary fault zone of the Kerimbas Graben (WBFZ) and the Seagap fault zone (SFZ). In the RB, natural gas migrates vertically along the WBFZ and preferentially accumulates in the deep-water turbidite sandstones of the footwall under the control of the fluid potential. Conversely, in the southern TB, the deep natural gas first migrates upward along the SFZ, then moves along the shallow branch faults in the sandstones on both sides of the SFZ.