Thermal maturity modelling of the source rocks of the Mandawa basin, Southeastern Tanzania

Petroleum system in the Mandawa basin has been extensively studied. From all studies, the timing of source rocks thermal maturities in relation to the reservoirs and traps in the Mandawa basin is little known. This study employed the borehole data (lithostratigraphy and source rocks properties) from Mihambia well and boundary conditions (basal heat flow, Paleo water depth and Sediment water interface temperature). These data have been employed in performing 1D-modelling of the burial history, paleo temperature evolution, thermal maturity and evaluating the timing of hydrocarbons generation of the Mandawa source rocks. The burial curves of the Mandawa basin revealed slow, moderate and high subsidence/sedimentation rates. These rates appear to be controlled by tectonic events. The high subsidence/sedimentation rate during Early Jurassic led to deposition of source rocks and coincides with Gondwana rifting. During Gondwana rifting, the upwelled mantle causes heat flux into the basin. The modelled basin temperature was sufficient for thermal maturation of the source rocks. The Mandawa source rocks begin to generate oil during Aalenian (172 Ma) and the entire source rocks entered oil window during Tithonian (146 Ma). During oil generation the Mihambia sandstone (as reservoir) and Mihambia claystone (as seal) was in place, as the traps of generated oil. The modelling of this study suggests that only oil was generated. Hence, defines the Mandawa basin as peculiar basin to hosts only oil with exception from other basins along east Africa coast, where mainly gas discoveries have been reported.