Spatial Variations in Hydrocarbon Generation and Expulsion, Southern Tunisia

Abstract

Since 2003 Pioneer Natural Resources Tunisia Ltd. has participated in the drilling of 42 wells in southern Tunisia, made a number of discoveries and recorded the presence of hydrocarbons in reservoirs of Ordovician, Silurian, Devonian, and Triassic age. This presentation builds on prior work, but specifically focuses on basin models aimed at exploration acreage operated by Pioneer. Subsequent to the deposition of Paleozoic source rocks, the Ghadames Basin experienced uplift and erosion related to at least 4 major orogenies. The amount of erosion varies across the acreage studied and the results from 3 of the study wells are presented to illustrate the varying impact of basin tectonics on source rock generation and expulsion. Basin models, constrained by bottom-hole temperatures and vitrinitre reflectance equivalent data, support 2 phases of hydrocarbon generation and expulsion from the Silurian Tannezuft hot shales, ie., during the Carboniferous and late Cretaceous/early Tertiary. In contrast, the Devonian Frasnian source rocks have been adversely affected by the Hercynian uplift and have only expelled hydrocarbons within the western portion of the study area. Hydrocarbon expulsion from the Frasnian source rocks occurred during late Cretaceous/early Tertiary.