Geopetroleum Evaluation of the Ordovician and Triassic Reservoirs in the Southern Part of Chotts Area (Southern Tunisia) and Maturity Modeling

Abstract

This study evaluates the geopetroleum assessment of the Ordovician series (El Atchane and El Hamra reservoirs) and the Triassic series (TAGI), in the Southern Chotts region, based on well logging data. The burial and thermal maturity history of the potential source rock Fegaguira Formation (Silurian in age) of the area, was accomplished using the BasinMod software. The generation and expulsion times of hydrocarbons in the region, as well as their quantities were also estimated. The Ordovician reservoirs (El Atchane and El Hamra) generally show the same petrophysical characteristics (the porosity of the two reservoirs varies between 5 and 12%) with a decrease in thickness from west to east until the total disappearance of the El Hamra Formation. This variation was related, on the one hand, to the bevelling of the Ordovician on the Telemzane arch and, on the other hand, to the erosive effects of the orogenic phases during Paleozoic (Taconic, Caledonian and Hercynian phases). The maturity history modeling of four wells in the south of the Chotts region shows that the Fegaguira source rock is mature and began generating hydrocarbons during the Early Cretaceous and expelled its hydrocarbons from the Paleogene in the wells 5 and 7 and from Cretaceous in the well 13 (at a SATEX of 10%). The Fegaguira source rock has not expelled in the well 19. The quantity of oil expelled by the Fegaguira source rock reached 36.3 bbl/acre ft rock and 33 bbl/acre ft rock in the wells 5 and 7 during Paleogene and 53.5 bbl/acre ft rock in the well 13.