Characterization Of Triassic Hydrocarbon Source Rocks Of The Mandawa Basin, Tanzania

ABSTRACT

Mandawa Basin is an onshore pull-apart basin located at the southern east coast of Tanzania and covers an area of 16,000 sq.km, it evolved during Permo-Triassic time by ENE-WSW extensional movements during Gondwana rifting and NW-SE extensional movements resulted from drifting of Madagascar during Jurassic time. Hydrocarbon exploration started in 1952, with the first deep exploration well (Mandawa-7) drilled in 1958 by BP company, there after ten exploration wells have been drilled up to date. The report (TPDC) shows that five wells have proven to have oil or gas shows, and five wells are dry without shows of hydrocarbons and have been abandoned. The main aim of the thesis is to characterize the source rocks potentiality and determination of the organic rich intervals of the Basin, namely, the Mbuo Claystone Member and the Nondwa shales. In order to define a potentiality of source rock. Detailed analysis of characterization parameters should be done, these include; total organic carbon (TOC), maturity level, net-to gross ratio, and organic matter type by integrating geochemical and well log analysis approaches. The results obtained from this study shows that both Mbuo claystone and Nondwa shales have poor hydrocarbon generation potential in their organic rich intervals. Using Passey’s method it shows that fair average TOC% values were encountered and less than 0.5 NTG for both Mbuo Claystone and the Nondwa shales using a marginal cut-off value of 0.5 wt.% TOC. The cross plot between derived TOC and geochemical parameters show that the source rocks were not worthy to be considered as potential but also the S1and S2 were independent to the thermal maturity and amount of TOC and mostly below the minimum value (1.0 and 5.0 mgHC/g Rock) for the source rocks to be considered as potential for hydrocarbon generation