Petroleum Potential and Modelling of the Devonian Aouinet Ouenine II and III Source Rocks in the Ghadames Basin, South Tunisia: Inferred Unconventional Reserves in Place

The intracratonic Ghadames Basin of South Tunisia is believed to have undergone several tectonic phases but the Hercynian phase is considered to be the most important given the amount of eroded sediment extending from Devonian to Permian. The basin encompasses two main supplying source rocks thought to have impregnated Paleozoic and Triassic reservoirs which are the Early Silurian Tannezuft source rock (hot shales) and the Middle-Late Devonian Aouinet Ouenine source rocks. The latter was probably the least appraised from a publication point of view. This research focused on the Devonian Aouinet Ouenine source rocks and tried to model their burial and thermal history and estimate the generated and expelled hydrocarbon amounts. An evaluation of non-conventional remaining hydrocarbon was also attempted. To this end, around thirty wells where source rocks were crossed were scrutinized. Various lithostratigraphic correlations were achieved based on thorough subdivision of the Aouinet Ouenine Group into four formations (AO I to AOIV). Aouinet Ouenine II (AOII) and Aouinet Ouenine (AOIII) formations were considered as being fairly to highly rich in organic matter and bear a good source rock potential. The N-S lithostratigraphic correlation, particularly, shows noticeable thicknesses variation of the Aouinet Ouenine group, thinning from South to North under the effect of the Hercynian unconformity. Burial and thermal modelling using the BasinMod software was performed via the integration of lithostratigraphic data, thermal data, known tectonic events, and geochemical data. The modelling allowed us to quantify the amounts of generated and expelled hydrocarbons and subsequently estimate the potential of oil left in place. Results show that the main source rock formations (AOII and AOIII) have generated average amounts of hydrocarbons and expelled only very small quantities, given the expulsion threshold that was not reached (SATEX = 11%). Approximately, it was estimated that the Aouinet Ouenine II Formation may still contain in the order of 73.68 × 109 bbls of oil in place, while the Aouinet Ouenine III Formation could still contain 62.9 × 109 bbls of oil in place. These reserves could be exploited as shale oil and constitute good amounts of unconventional reserves to be recovered.