GEOCHEMISTRY OF THE TENDAHO GEOTHERMAL FIELD, ETHIOPIA

Abstract

The Tendaho geothermal field is located in t he Afar
triangle (Northern Afar) about 700 km north-east of
Addis Ababa.
The Afar triangle is an area of active extensional
tectonics and basaltic magmatism from which the
Gulf of Aden, the Red Sea, and the Ethiopian rift systems radiate . Normal faults an d open fissures are the principal elements of the Afar tectonics. In the Tendaho geothermal field, three deep (1811m - 2100m) and three shallow (466m -516m) exploratory wells were drilled, of which four wells (one deep and three shallow wells ) are found to be potentially productive. The waters of productive wells are typical of Na-Cl geothermal waters with reservoir temperature of about 220-250?C. At Tendaho, a production test and feasibility study is currently in hand.

The main objective of the present stu dy is mainly to identify the recharge and the sub -surface temperature of the Tendaho geothemal systems. Previous work had been reviewed and water samples had been collected for chemical and isotope analysis in order to get full information about the Tendah geothermal system. After using different chemical and isotopic techniques, the following conclusions are given
.
? The water type of the Tendaho geothermal field is dominantly Na -Cl, neutral to alkaline geothermal water.

? The average reservoir temperature of the systems is about 220?C-250?C.

? The isotope result has indicated two recharge zones, the Ethiopian plateau and the Lakes district through the Southern Afar.