Geological and geochemical evaluation of shale gas potential of the Tanezzuft for-mation, Ghadames Basin, North Africa

Abstract

The Ghadames Basin is a poly-history Palaeozoic basin covering parts of Tunisia, Algeria and Libya. Exploration efforts in the past which targeted conventional hydrocarbon resources have been most successful in the Algerian segment. The aim of this research was to undertake a geological and geochemical assessment of the 'world class Silurian Tanezzuft Formation, model the timing of hydrocarbon generation and expulsion within the basin, all in a bid to evaluate its shale gas potential. Data from forty-nine (49) wells, which consist of total organic carbon (TOC), thermal maturity (Tmax), and kerogen (Hydrogen Index) were utilised for this study. TOC and Thermal maturity maps with cutoffs of 2wt.% and 1.0 Roequvalent which were generated show an increase of organic richness and maturity towards the West/NW. Subsequently integration of maps show favourable shale gas potential in a major 'sweet spot' area in the Western Ghadames Basin, with geological and geochemical characteristics that compare favourably with established similar aged gas shales in the US. Furthermore, 1-D basin models generated from an existing well and a pseudo well within the identified sweet spot area using a linear heat flow model reveal a good potential for thermogenic gas adsorption as well as an upside for shale oil. However, the risk and uncertainties associated with the shale gas development may be heightened due to non-technical issues such as political instability, access to technical support, water supply for fracking operations as well as potential environmental issues such as groundwater contamination with methane and induced seismicity arising from hydraulic fracturing.