Title: Reducing exhumation uncertainties in basin modelling: Source rock maturation history of the Southern Chotts Basin, Central Tunisia
Jos Kwakman, Pierre-Olivier Bruna & Giovanni Bertotti
Department of Geoscience and Engineering, Delft University of Technology, Delft, The Netherlands
Event: Abstract GeoUtrecht2020
The primary reservoirs present in the Southern Chotts Basin, Central Tunisia, are located within Triassic-, Permian- and Ordovician units. They are mainly sourced by the Silurian - Lower Devonian Fegaguira Fm. and its Hot Shale member. The Hercynian Orogeny has reworked the Palaeozoic package, removing the Devonian - Carboniferous and most of the Permian deposits in the Southern Chotts Basin. This resulted in a diachronous unconformity in the present-day stratigraphy.
Constraining estimated sediment deposition and subsequent erosion at unconformities is crucial to predict timing of source rock maturation. This study aims to qualify and quantify the effects of several simplified burial- and thermal histories on the timing of source rock maturation, understand migration pathways to predict sweet spots and gain insight in Mesozoic burial.
Thermal history calibration was performed and allowed modelling source rock maturation in the basin's kitchen area. Hydrocarbon generation occurs in two phases separated by a phase of stable maturity during Hercynian exhumation. Pre-Hercynian generation is unlikely to result in preserved accumulations in post-Hercynian traps. Renewed maturation in Jurassic - Cretaceous times likely sources present-day hydrocarbon accumulations in post-Hercynian traps. The number of phases- and maximum burial depth associated with the Hercynian Orogeny determine the amount of missed pre-Hercynian hydrocarbons and the timing of renewed maturation in the Mesozoic.
Sensitivity analysis on estimated Hercynian erosion further constrained associated maximum burial and -hydrocarbon generation. 2D basin modelling captures migration pathways and helped predicting sweet spots. Subsidence analysis shows Mesozoic subsidence occurs as a result of pulsed rifting with possible short-lived uplift phases, indicating the diachronous nature of tectonics in the Southern Chotts Basin.