ASAL Gale-le-Koma Current Surveys PRESENTED BY Ayan AHMED SUGE Geologist
Geothermal Sites In Republic of DJIBOUTI Geother Geothermal mal sites sites 1. Lake Abhe 12. Nord Ghoubbet (Afaî- Bolli Daar) 2. Sakalol 13. NE Ghoubet (Assa Foo) 3. Arta 14. Modayto (N Gaggade) 4. Asal Fialé 15. Obock 5. Asal gale-le-koma 16. Okililaeou (SE Gaggade) 6. Balho 17. PK 20-Ambado 7. Daggadé (W hanlé) 18. Roueli 8. Dimbir-Didir (W 19. Sakalol Gaggade) 9. Garabayyis ( E 20. Tadjoura Hanlé) 10. Karapti-san 21. Agna-Galafi (NW Hanlé) 11. Manda Inakir 22. Sud Est Ghoubbet
ASAL Gale-le-Koma Current Surveys • The most popular site in the World • The Lake Asal is the only lake that is situated 157m below the sea level Hydrogeologic : supply of seawater from the •A lot of studies from 70’s to 80’s and a Ghoubbet with flow to Lake Asal ( red and blue arrrow new drilling was done in 2016. shows movement of hot and cold water)
ASAL and Gale-Le-Koma Current Surveys The best-studied site in the country for 50 years (BRGM,CNRS,AQUATER,REI/ISOR);volcanology,tect onics,hydrogeochemistry,geophysics(MT,gravimetre,seis micity), 6 reconnaissance holes made on Asal including A5 at the edge of the Fialé caldera. Heat source: magmatic chamber (1200 ° C to 3-5 km); good permeability; which cooled the geothermal reservoir (1978-1987) reheated since filling the magma chamber between 1988 and 2001 Geology : Fault Rift Assal NW-SE, NNW normal fault from an older Rift E-W fracture mainly parallel to the Aden Ridge ● Carracteristic of the reservoir • Reservoir is situated betwen 300-1500 mètre • Temperature : 130 ° C to 190 ° C • Sea water flowing from the sea to Assal Lake
A1 A3 GLC-1 A6 A2 A4 A5 Geology
Geophysics study Good conductors identified by geophysics (TDEM and MT). shallow reservoir (300-600 m) at 120-140 ° C salinity is around 50g/l. Based on the old and the update studies from ODDEG, the location of Gale Le Goma GLC1 drilling well was determinate close to Assal 3
ASAL and Gale-Le-Koma Conceptuel model H NE-SW cross section through the Assal rift zone An up-flow is expected to be beneath the Lava Lake and outflow to south and west at 200-500 m depth. The up-flow zone is composed by anhydrite or other hydrothermal alteration minerals. The blue rectangles represent leaky zones where inflow of cold water from east (from the ocean) has cooled the rock at ~600-1000 m depth. Shallow reservoir between 500-700m.
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PK-20 AMBADO Current Surveys Geographycal Location 11 °28’09 ; 43°00’18 Acces road: close to the city Local developpement: urbanisation and connect directly to the electrical connexion( PAM, Port, Free zone PK20) Temperature T˚C min T˚C max of the Reservoir Temp. 103˚C 119˚C Team Estimated for this Temperature 42˚C 73,6˚C Study of water well Geophysics Geochemestr Geologist Technicians ist 7 3 6 10
Geological Study The region is affected by NW-SE ,WEN-ENE and N-S faults. Correlation The convective hydrothermal system which has Correlation of well water warmed the surface water table in the basalts of the drilling: Awrolofoul 6, 2, 5 Aw6= 73,6 ˚C at 114,43 Gulf, but no particular surface manifestation ( Blind geothermal system). Aw5= 30m3/h Aw2= 56.2 ˚C at 98m We found that the water from water wells are getting hot when 2 systems of junction of faults NW-SE and E- W
Geochimical Study • The team take a sampling from 26 drilling wells in the prospect zone of PK20Ambado. • The samples was analyzis in collaboration with BGR. • The composition of the water have a presence of sodium chloride. The analysis of the water revelated that the water is immature and so the geothermometer is not applicated to estimate the reservoir temperature. But from the old studies, the geothermometers indicate a temperature around 103-119 ° C
Geophysical Study • The area of the propect project was found a thermic anomalies because of the hot temperature from the drilling wells was. • This map indicate the gravimetric on the MT station. Carte de localisation des sondages MT et gravimétrie. En étoiles rouges les points MT et les points noirs les sondages gravimétriques. Les triangles bleus clairs correspondent aux forages d'eau présentant une anomalie thermique.
Conceptuel Model of the prospect project PK20Ambado • Thermical Anomalie was observe from the water wells.(orange) • MT revelated a conductor anomalie with the gravimetric data (blue) • This data revelated also a negative residuelle anomalie • Finaly this 3 anomalies put together give us a sector that we selected for the exploration drilling well.
MT and Gravimetric results Anomaly gravimetric and MT combined are found in the same location around the zone of Awrolofoul at PK20 Ambado. The temperature are high in the junction beteween the Gulf Basalt and Somali Basalt. The recharge of the reservoir is coming from a meteoric water of the river. 3Drilling well are planned in 2018.
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