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Borehole geology of well Asal-5, Asal geothermal field, Djibouti

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Titill: Borehole geology of well Asal-5, Asal geothermal field, DjiboutiBorehole geology of well Asal-5, Asal geothermal field, Djibouti
Höfundur: Jarðhitaskóli Háskóla Sameinuðu þjóðanna ; Khaireh, Ali Elmi
URI: http://hdl.handle.net/10802/23042
Útgefandi: United Nations University; Orkustofnun
Útgáfa: 1989
Ritröð: United Nations University., UNU Geothermal Training Programme, Iceland. Report ; 1989:6
Efnisorð: Jarðhitarannsóknir; Jarðhiti; Jarðboranir; Borholur; Djibouti
ISSN: 1670-7427
Tungumál: Enska
Tengd vefsíðuslóð: http://www.os.is/gogn/unu-gtp-report/UNU-GTP-1989-06.pdf
Tegund: Bók
Gegnir ID: 001512307
Athugasemdir: Myndefni: kort, línurit.
Útdráttur: This report describes the borehole geology of the well Asal-5 in the Asal geothermal field in Djibouti. This well was sunk down to 2105 m depth in the "inner rift" in order to explore there the temperature, permeability and the fluid characteristics of the area. The well penetrated a lava succession of olivine-, ferro- and trachybasalts as well as trachytes. Intrusive rocks are inferred at four depth intervals. The well showed a very low permeability and could not be discharged. Three aquifers were located above the production casing, the largest and the hottest one being at 500-550 m. Three minor aquifers were found in the production part of the well below 1600 m depth. The rocks show an extensive water/rock interaction where the intensity as well as rank of alteration increases with depth. The hydrothermal assemblage above ca. 1700 m depth indicates a much higher temperature condition than presently measured which clearly shows that the geothermal system has cooled down by as much as 200 C at 1000 m depth. A vague indication of retrograde mineralization, by the common occurrence of smectite down to 1000 m depth and laumontite presence at 600 m and 800 m depth, may indicate a lowering of temperature to below 200 C.


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