The Asal rift, located 80 km west of Djibouti, is one of the active " rifts-in- rift " structures of the Afar depression, a transition between the Gulf of Aden and the Red Sea ridges (Fig.1).

Attention was drawn to this zone because of the presence of a graben structure, and of geochemical particularities of various hot springs. Two wells were drilled on the S-W margin of the rift, at locations chosen mainly from geological considerations. The first hole reached a hot water geothermal reservoir, the second, one kilometer away, was dry.

Both wells found, from top to bottom, a recent basaltic series, then a thick rhyolitic volcanic series, and finally an old tectonic, tilt e d, basaltic series, where the reservoir is located. The first well was drilled to a depth of 1130 m, where heavy mud losses occurred, while the second well reached 1550 m. An important normal fault appears to separate the two wells.

The first well, which had to be induced into production by air-lift, was used for extensive well testing.

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