A basin modeling study of the Ghadames Basin, Western Libya: Implications for unconventional hydrocarbon potential of the Silurian Tanezzuft Formation

The Lower Silurian shales of the Tanezzuft Formation in the Ghadames Basin in Libya and Algeria have long been recognized as the source of hydrocarbons trapped in conventional reservoirs. In the last few decades, commercial quantities of hydrocarbon extraction from unconventional reservoirs, especially in North America, have been made. Organic matter-rich shales and carbonate mudrocks have been recognized as potential shale gas and shale oil plays. Lately, hydrocarbon exploration and production activities have expanded to many parts of the world; successful activities have been recently reported from the Jafurah Basin in Saudi Arabia and the Ordos Basin in China. The current study aims to assess the unconventional hydrocarbon resource potential of the Silurian Tanezzuft shales in western Libya, part of the Ghadames basin, using a basin modeling approach. First, a thorough review of the literature on the geological history and petroleum geology of the Ghadames basin has been conducted. Secondly, a 2D basin modeling study was conducted on a 480 km-long geological cross-section. Following model calibration, model predictions on the burial, temperature, and hydrocarbon generation histories as well as oil and gas in-place for the Tanezzuft shales have been evaluated and discussed. Accordingly, the first major burial took place before the Hercynian orogeny and, at the depocenter, the Tanezzuft shales entered the oil generation window during the Middle-Late Carboniferous. The Hercynian orogeny led to regional uplift and erosion of the sedimentary cover and shallowing of the Tanezzuft shales, leading to a drop-in temperature and frozen thermal maturity. The second burial episode took place between the Triassic and the Late Cretaceous, leading to increasing maturity of the Tanezzuft shales and major oil and gas generation, especially in the central basin. The effect of Alpine orogeny on burial history, maturation, and hydrocarbon generation from the Tanezzuft shales in the basin is considered to be very significant Formation pressure drop in the Tanezzuft shales during uplift brought about the Alpine orogeny might have caused the escape of some gas. In this context, two main factors, namely burial history and adjacent rock lithology, stand out as very critical for the present-day gas content of the Tanezzuft hot shales. Model predictions suggest that the potential for shale oil and shale gas for the Silurian Tanezzuft hot shales seems to be high, and the spatial distribution of this potential parallels the maturity distribution of the shales in the basin. Shale oil potential is high in marginal areas where the Tanezzuft shales are in the oil window, and shale gas potential is important in the deeper parts of the Ghadames Basin in western Libya. This assessment based on model predictions obviously needs verification and hopefully future exploration activities will meet this need.