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ORGANIC GEOCHEMICAL ASSESSMENT AND SHALE GAS POTENTIAL OF LOWER SILURIAN ORGANIC RICH SHALE IN THE GHADAMES BASIN, NORTH AFRICA

The Silurian organic rich shale is the main source of hydrocarbons in the Ghadames Basin in North Africa. The basin has been widely characterized as a source rock for Ordovician oil and gas; yet understanding this shale as a shale resource play remains problematic and challenging. In this study, geochemical and mineralogical analyses of drill cuttings derived from five wellbores were carried out to evaluate the unconventional potential of Silurian organic rich shale. The results of geochemical analysis show that the present day total organic carbon (TOC) of this shale is generally medium to good, varying between 1 and 5 wt%. The hydrogen index (HI = 55–201 mg HC/g TOC) and Tmax (435–454 °C) values indicate type II kerogen in a mature state and its ability to generate wet gas. The results of mineralogical analysis show that clay minerals dominate in all samples of Silurian shale (39–58%) followed by quartz (16–37%). Geochemical parameters such as Mo, V, As, Zr and TiO2 indicate that these shales were deposited in anoxic conditions and were sourced from intermediate igneous rocks. In order to evaluate the potential of Silurian shale as oil and gas source, in this work, the chemostratigraphy technique was applied to identify the provenance of silica in shales, to characterize the shale brittleness and model a correlation between the mineralogy and organic matter content. In conclusion, the Silurian organic rich shale in the Ghadames Basin exhibits good characteristics for shale resource hydrocarbons production.