Organic geochemical study of Permian series from the Jeffara and Dahar areas (Southern Tunisia): Identification and characterization of a Tunisian Permian source rock

Abstract

Permian rock samples from four wells drilled in the Jeffara (J1 and J2) and Dahar (D1 and D2) areas of southern Tunisia were evaluated using the Rock-Eval® Shale Play™ method. Quantification of most liquid hydrocarbon compound families released at specific temperature range for the Sh0 and Sh1 as well as Sh2 and S3 parameters was achieved with subsequent calculations of appropriate indices. In addition, stable carbon isotopes evaluation of Permian samples was carried out in order to estimate the origin of their fossilized organic matter. Biomarker analyses were also undertaken on Permian samples and other proven Paleozoic source rocks samples of the study area (Ordovician Azzel and Upper Silurian Fegaguira formations) for comparison purposes.The results show that the Permian series encompass highly-rich organic matter intervals which may exceed 5%. The organic matter is of type II2-III, proven either by the Rock-Eval®, carbon isotopes and biomarker data. Permian samples from three wells (D1, D2, and J2) are found mostly at an early mature stage. Contrary, Permian samples from the J1 Well show abnormal Tmax temperatures testifying an overmature stage which could be related to abnormal heat flow around the Jeffara area. The depositional environment of the organic matter-rich Permian intervals is mainly suboxic of normal salinity, similar to the other Paleozoic investigated source rocks in the study area. Overall, this research comes to validate the occurrence within the Dahar and Jeffara areas of an active Permian oil/gas prone source rock, competitive to the other proven Paleozoic source rocks.