Geochemical Characteristics and Hydrocarbon Generation Modelling of Early Triassic to Late Cretaceous Formations within Ogaden Basin, Ethiopia

Abstract

The major goal of this study is the evaluation of the source rock of Ogaden Basin using Rock-Eval Pyrolysis, Vitrinite reflectance (%Ro), and well log data of the Permo-Triassic and the Mesozoic sequences including Karro, Hamanlei, and Urandab Formations. Burial history and level of thermal maturity of the Bodle-1 well, the Calub-1 well and the Hilala-2 well were modeled based on the calibration of measured %Ro and Tmax against calculated %Ro model. The calculated Total Organic Carbon (TOC) content from the well log data compared with the measured TOC from the Rock-Eval pyrolysis in the three mentioned wells is shown to match against the shale source rock. The total organic carbon (TOC) content value ranged from 0.48 to 4.24 wt % while the S1 and S2 values ranged from 0.05 to 0.76 (mg/g) and 8.52 to 27.88 (mg/g) respectively. Hydrogen index (HI) versus oxygen index (OI) plot has shown that the organic matter is predominately made up of type III kerogen (gas prone) while Tmax and HI indicated mixed type II/III kerogen (25% of Urandab Formation, 40% of Bokh Formation and 15% of Hamanlei and Adigrat Formations). Tmax was assessed from vitrinite reflectance (Ro) readings for Bodle-1, Calub-1 and Hilala-2 wells showed an average vitrinite reflectance values in the range of 0.5-1.4 VRo%, 0.35-1.08 VRo %, 0.55 – 0.69 VRo % respectively. The developed burial history models have revealed that Bokh Shale hydrocarbon generation has been started during lower Jurassic, and presently hydrocarbon generation has been started within the “oil window” while Urandab Shale is immature to fairly mature.