An Overview of the Geothermal Regime in Sirt Basin, Libya: The Geological Role and Heat Flow Studies

Bottom hole temperatures (BHTs) and static formation temperatures (DSTs) of 70 deep exploratory
wells are used to evaluate the geothermal regime in the northeastern part of Sirt Basin. The structural
and stratigraphic evolution of the Sirt Basin was developed during four main tectonic phases
corresponding to plate reorganization, which is tied to the evolution of the Atlantic and the Tethys. The
geothermal gradients were calculated using the corrected BHT’s and the heat flow has been
estimated. Interpretation of the geothermal data, utilizing sub-surface maps and isothermal geologic
cross section, revealed a shallow, local semi-thermal reservoir of Oligo-Miocene age (at depths <
1000 m). The geo-thermal gradients and heat flow values of this reservoir are ranging from
40>60°C/Km and from 80 up to >130 mw/m2, respectively. At deeper depths (>1000 m until the
maximum depth of investigation), the area has more or less moderate to low geothermal gradients
that range from 40 to <20°C/Km and heat flow <80 to <20 mw/m2. The study indicates that the vertical
and the lateral variations of the formation temperatures, geothermal gradients and the heat flow
values are controlled by the structural, groundwater movements as well as lithological and thermal
characteristics of the subsurface sequence.