Is the offshore southern Tanzanian Basin an atypical igneous-sedimentary petroleum system?

Abstract

The northern region of the offshore southern Tanzania contains structurally controlled hydrocarbon discoveries. The Permo-Triassic, Jurassic, Cretaceous and Cenozoic source rocks are reported to have possibly charged the existing hydrocarbon reservoirs in the region. However, there is no a detailed record of possible heat sources that may have matured the reported source rocks. Additionally, focused academic research on the possibility of different petroleum traps in the area has also not been done before. This study has used conventional 2D seismic interpretation to reveal presence of several igneous intrusions in the study area. The revealed igneous intrusions include igneous dykes and sills present in the Cretaceous and Cenozoic parts of the studied stratigraphy. Together with the existing burial depth, the associated magmatic heat is interpreted to have facilitated maturation of the Cretaceous-Cenozoic source rocks in the region. This suggests that the offshore southern Tanzanian Basin contains an atypical petroleum system where source rock maturation did not entirely rely on burial temperature. The igneous intrusions have also created hydrocarbon migration pathways from different stratigraphic levels. This is reflected by fracturing of the immediate reservoir intervals and seal rocks above the mapped igneous dykes. The used seismic datasets have also allowed mapping of structural, stratigraphic and combination traps in the study area.