Surface study of a shallow geothermal site for Abhé Geothermal Village Project (Djibouti)

The site selected for the GV project in Djibouti Republic is isolated, 50 km from the National
Grid and Electrical High Voltage line linking Ethiopia and Djibouti. The local population is pastoralist
and semi-nomadic as the shore of the lake allow for permanent pastureland. Previously dispersed on the
hills surrounding the lacustrine plain, the families tend to group around a school which opened a first
class in October 2020.
The area - characterized by spectacular carbonaceous travertine chimneys built from hot-springs
and fumarole hydrothermal deposits – was studied in the previous years for its geothermal potential in
the perspective of electricity production for the national grid.
The target of the present geoscientific investigation was triple: (i) Medium-High temperature resource
for electricity production with an ORC; (ii) Hot water production for direct uses applications including
SPA and (iii) drinking water production for the village, the school and touristic installations. All
resources targeted at shallow depths (a few ten to hundred metres). Field works included structural
geology, volcanic petrology, hydrothermal mineralogy, and petrophysics, followed by laboratory
studies.
One of the specificities of the project is the engagement – in parallel with the work on land - of
a detailed drone survey for both the topography and structural geology (visible wavelength) carried on
day-time and an Infra-Red survey producing a detailed mapping of the thermal vents carried in the night
and early morning before sun-rise. This allowed to discover and measure the temperature of several
geothermal vents unmapped and unsampled until now, then further measured and sampled for physical
and chemical analysis. The Geochemical gas isotopic composition helps precise the magmatic origin of
the heat source, whereas the water chemistry allows to map the hydrothermal plumbing including water
mixing at shallow depth.
From the joint analysis of a large set of data: gravity, geological survey, satellite images
interpretation and electric resistivity profiles, and the detailed magnetotellurics the 3D pictures of the
geothermal fluid plumbing will be drawn. As a result, a geothermal conceptual model allows to propose
shallow depth drilling sites and characteristics at for both electricity production from an ORC plant.