Geohistory Reconstruction and Maturity Modelling in the Southern Pletmos Basin, Offshore of South Africa

Abstract

Despite the undergoing exploration and research for hydrocarbons during the recent decades, the hydrocarbon potentials of existing source rock(s) in the Pletmos basin still remain enigmatic. The basin has undergone rifting and transforms processes during its evolution in a manner that its present-day architecture and geodynamic evolution can only be better understood through the application of a multidisciplinary and multi-scale geo-modelling procedure. In the study, thermal modelling and reconstruction of burial history of the source rocks in the southern depocenter of the Pletmos Basin has been investigated through an integration of data and methods. Through geohistory Modelling, an integration of the acquired multidisciplinary dataset allowed us to reconstruct the burial history, basement subsidence, vertical fluid flow, and the changes in rock properties (i.e. porosity, permeability, pressure and fluid flow rate) both in time and depth, as well as established a reliable tectonostratigraphic framework of the Mesozoic sedimentary infill. Then based on the reconstructed burial history, thermal history was reconstructed by modifying the paleoheat flux to minimize variances, and comparing between measured borehole and predicted vitrinite reflectance and Tmax (thermal indicator) values. These enable us to achieve an improved understanding of the subsurface controlling processes that might have led to the sedimentary infill and resulted to the heat-flow distribution and present-day thermal maturity of the source rocks in the Basin. The approach gives us the opportunity to considered the geodynamic evolution events from Mesozoic (Upper Jurassic) rifting to Cenozoic (including major uplifts, erosion and subsidence, and the Shona Buvet hot spots). Here we present some selected results, from the burial and thermal history modelling reconstructions of the sedimentary geothermal evolution and thermal maturity levels of the source rocks at selected well locations within the area. Likewise, this study has provided supplementary information that aids towards understanding the Petroleum System(s) of the Basin.