Petroleum System Modelling of Onshore Mandawa Basin - Southern, Tanzania

Abstract

The Mandawa Basin is located along the coast in the southern part of Tanzania, and is potentially one of the most hydrocarbon prospective in the country, as it believed to contain all the essential petroleum system elements. Hydrocarbon exploration and drilling in the basin has been done since the 1950 s but, in spite of the considerable exploration and drilling activities that have been carried out, no economical discoveries have been made. Gas and oil shows in a few wells significantly demonstrate however the presence of an effective petroleum system.The petroleum system modelling approach has been used to create a 3D petroleum system model of the basin, by incorporating the seismic horizon depth maps and input data from 1D calibrated modelling of the wells. The available measured data; temperature and vitrinite reflectance were used in model calibrations.The modelling results suggest that although the Mandawa Basin contains an effective petroleum system, the basin s formation history; in particular rifting episodes, salt deposition and heat flow have significant impact on the present petroleum system of the basin. Rapid subsidence, followed by periods of uplift and erosion affect both sediment deposition and trap formation and hence hydrocarbon generation, migration and entrapment.Maturity modelling shows that the Nondwa shale and Mbuo claystone are potentially the main hydrocarbon generating source rocks in the basin, which can have generated both oil and gas. Hydrocarbon accumulation prediction reveals that the Mbuo sandstone is the main potential reservoir of the generated hydrocarbons. However, in spite of high generation, most of the hydrocarbons can have been lost due both improper trapping and trap leakages. Furthermore, the modelling suggests that the southern part of basin is more prospective than the northern part, although more data, structural interpretation, risk analysis, and migration modelling would significantly improve the current results.