| Title | Nord-Ghoubbet Geothermal Site, Djibouti Republic |
|---|---|
| Authors | Abdou Mohamed Houmed, Abrourahman Omar Haga, Jacques Varet |
| Year | 2012 |
| Conference | ARGeo |
| Keywords | Tadjoura, Nord-Ghoubbet, hydrothermal, geophysics, tectonics, faults, rotation |
| Abstract | Resulting from a regional consideration of the whole Afar, for ranking the best geothermal sites combining geodynamic and hydrogeological approach (J. Varet, Argeo meeting, 2011), the area located to the north of the Ghoubbet Rift appeared to be the most promising for geothermal energy developments in the Djibouti Republic. This ¡§block¡¨, 10km long and 6km wide, covered at the surface essentially by the recent basalts of the gulf that is, emitted during the early stage of penetration of the Aden Ridge through the Gulf of Tadjourah, 4 to 2 My ago (O. Richard and J. Varet, 1979) benefits from unique geological conditions: - The immediate vicinity of the Ghoubbet active spreading segment, with a shallow anomalous (partially melting, 1300¢XC) upper mantle at 7km depth, providing an important and safe (regularly renewed, hence renewable) heat source for the geothermal field. - A tremendous fracturing of the whole block (made at the surface of recent basalts of the gulf) with at least 3 directions of open faulting with transverse components (NW-SE, NNW-SSE and NE-SW), providing a good fracture permeability of the reservoir. This particular tectonic setting is of course due to the vicinity of the transform faulting linking Ghoubbet and Tadjourah oceanic rift segments. But it also results (as shown by Manighetti et al. 2011) from the fast rotation of this brittle block. Numerous fumaroles and hot springs, some with important silica deposits, affecting the whole block, testify to the leakage of the geothermal reservoir due to the fairly active tectonics of the site. - Good reservoir conditions are also expected from the geology itself, as very important detrital deposits accumulated there, for the last 5My, underneath the more recent basalts, due to the up-rise and concomitant faulting and erosion of the whole area located North before and since the early stages of opening of the Gulf (up to 1000m high Dalha basaltic plateau and the famous Day mountain). - This reservoir should also benefit from relatively low salinity fluids ¡V certainly the best for Djibouti Republic - due to the long lasting flow of water from the Day Mountain downstream towards the Gulf for the last few My. Preliminary geochemical and geophysical studies were undertaken in the area by BRGM, and more recently MT and geo-electric surveys have been conducted by the CERD. Through this proposals were made for locations of exploration wells. However the investigation, presently limited to the immediate surroundings of the major surface hydrothermal manifestations should be extended to the whole area down to the sea shores. |