The Asal Geothermal Field (Republic of Djibouti)

Abstract

The Asal region is located along the rift connecting the Red sea to the Gulf of Aden through Afar. It is a typical segment of the rift valley characterized by active tectonic, seismic, volcanic and hydrothermal activity. For this reason it was selected by BRGM in 1970 as a target for geothermal exploration. Data collected using exploration and drilling of this area have enabled us to draw a model of the geothermal system. A tholeiitic magma chamber at a temperature of 1,200°C located at a depth of 5 to 8 km is overlain by a fractured system where brine circulates in chemical equilibrium with the basalt. This system is locally overlain by dry steam zones in the most fractures central part of the system. Superficial water of meteoric origin circulates in the upper part of the system, on the margins of the rift, whereas sea water circulates along the open fissures of the rift axis from the Ghoubbet to Lake Asal. The Asal geothermal field can support an installed capacity of several tens of MW, far above the needs of the Republic of Djibouti. Preliminary production tests show that separation conditions can be found allowing us to master silica and sulphide scaling probes. Cu, Zn, Pb and Ag deposited by the fluid may also have an economic value.