Simple modelling of geothermal resources in the Asal Rift area, Djibouti

Abstract

The Asal-rift geothermal field is located in the Ghoubhet Gulf area near Asal Lake in Djibouti. It is the most explored geothermal field in the country. The first geothermal investigation was undertaken in 1975, by the French Geological Survey (BRGM). This investigation lead to the discovery of a high-enthalpy geothermal reservoir. With the financial support of the World Bank and UNEP, six deep boreholes were drilled in the field. The most recent well, GLC-1 in Gale Coma, was drilled by the Government of Djibouti in September 2016. The Asal area has been described as a segment of the world oceanic rift system by earlier investigators. Well A-2 was damaged, wells A-4 and A-5 were impermeable although very hot, but wells A-1, 3 and 6 produced extremely saline fluids from 1000-1300 m depth where the aquifer temperature is about 260°C. Conceptual models are used to describe or illustrate essential features of geological situations and delineate the principal processes in the system, by focusing on data providing information about temperature, pressure and fluid flow. In this study, the conceptual model of the Asal geothermal system has been updated and a Monte Carlo volumetric assessment of the intermediate temperature reservoir in the area performed. Extensive exploration and field-wide production tests need to be performed to accurately estimate the actual size and capacity of the Asal geothermal reservoirs.