STATE OF KNOWLEDGE OF THE GEOTHERMAL PROVINCES OF REPUBLIC OF DJIBOUTI UNU training KENGEN Naivasha, Kenya, November 2007 JALLUDIN Mohamed Djibouti, CERD
GEOTHERMAL EXPLORATIONS IN DJIBOUTI FIRST PHASE Preliminary field studies Asal rift geophysical studies First geothermal drillings in Asal Rift geothermal area Nord-Goubhet geophysical studies SECOND PHASE Hanlé-Gaggadé exploration (field studies and gradient wells) Hanlé geothermal drillings Asal rift new drillings and geophysics Scaling and corrosion study of Asal rift deep reservoir
GEOLOGY AND SURFACE MANIFESTATIONS
HANLE GEOTHERMAL EXPLORATION AREA Republic of Djibouti Lake Asal Hanle plain Gaggade plain HANLE 1 HANLE 2 Lake Abhe
HANLE-GAGGADE GEOCHEMICAL STUDIES (AQUATER-CERD 1983)
-50 ELECTRICAL SURVEY OF HANLE PLAIN (AQUATER-CERD 1983) -50-50 -150-100 -50 50 0 " Yoboki -150-100 0-50 Legend -100 Altitude of the T group (resistant) -150 Disconinuity -250 0-200 3 1.5 0 3 Kilometers -50 0
HANLE GRADIENT WELLS TEWEO1 GARABAYIS2 30 C 100 C 130 C Garabayis1 2 /100m 121.7 C Teweo1 1.3 /100m 43.7 C Coarse alluvium Fine sand Mud and silt Rhyolite Basalts 452 m Garabayis2 3 /100m 80.8 C 500m
Depth m Depth m HANLE DRILLINGS 40 50 60 70 80 90 70 80 90 100 110 120 130 0 100 200 Temperature C 0 100 200 Temperature C 300 400 500 600 700 300 400 500 600 800 900 1000 700 800 HANLE 1 HANLE 2 1100 1200 1300 1400 1500 1600 1700 900 1000 1100 1200 1300 1400 1500 Alluviums Rhyolites Trachytes Basalts 1600 1700 1800 1900 2000 2100
HANLE EXPLORATION OUTCOME Hanlé 1 (1623 m), 72 C at 1420 m Hanlé 2 (2038 m), 124 C at 2020 m Permeability Hanlé 1: rhyolites, contact rhyolites-basalts, scoriae, dry below 800 m Hanlé 2: basalts, scoriae, dry below 450 m Bottom hole core of Hanlé 2: 18.8 My Thick crust with 24 C/km to 36 C/km
Asal Geothermal area Republic of Djibouti
SURFACE MANIFESTATIONS AND GRADIENT WELLS
GRAVIMETRIC SURVEY. BOUGUER ANOMALY (BRGM 1993)
TEM SURVEY OF THE ASAL RIFT (BRGM 1993; ORKUSTOFNUN 1988) Altitude -100m Altitude -200m Altitude -300m
Main geochemical results (San Juan et al. 1990) Thermal fluids result from basalt-sea water interaction This interaction is influenzed by evaporation Some hot springs could be mixed with Asal lake waters The boron anomaly in the borehole fluids suggests a vapour dominated system
Profondeur m Temperature profiles Asal geothermal area Température C 0 100 200 300 400 0 500 Well Depth (m) Temp. Max ( C) Temp. Gradient ( C/100m) 1000 A1 1145 261 18 A2 1554 235 14.3 1500 2000 ASAL3 ASAL4 ASAL5 A3 1316 280 15.51 A4 2013 345 15.2 A5 2105 360 15.2 A6 1761 280 12.75 2500
Depth m Depth m Interpretative cross section of ASAL 3 40 60 80 100 120 140 160 180 200 Asal 0 rift Geothermal area Temperature C 100 200 ASAL4 40 60 80 100 120 140 160 180 200 220 0 Temperature C 100 200 ASAL 5 300 400 Asal series 300 400 500 500 600 600 700 800 900 1000 Stratoid series Dalha basalts 700 800 900 1000 1100 1316 m 1100 1200 Alluviums Clays Hyaloclastites 1300 1400 1500 Rhyolites Basalts Trachytes 500 m 2013 m 1600 2105 m
Total flow rate (ton/h) Total flow rate (ton/h) Wt (ton/h) Production curves of ASAL 3 400 350 300 250 200 150 100 50 0 11/8/87 20/9/87 30/10/87 9/12/87 350 300 250 200 150 100 50 SEPT.89 DEC.89 MAR.90 Production curve of ASAL 1 100 80 60 40 20 0 10 12 14 16 18 20 22 WHP (bar) 0 5 10 15 20 WHP (bar)
Scale deposits in 6 inch production liner Asal 1 geothermal well (BRGM-CERD 1981) 180 µm Spharelite Sulphide deposits 300 m depth Baryte x3000 Silencer deposits Galena CERD Republic of Djibouti
Pressure bar ( Pi - Pwf ) / QN Drawdown bar ( Pi - Pwf ) / QN Asal 3 well testing data 0 0.5 Drawdowns. ASAL3 130 120 110 Multirate drawdown. ASAL3 1 155-225 ton/h 1.5 300-357 ton/h 2 225-300 ton/h Time hour 79-130 ton/h 2.5 0.01 0.1 1 10 100 100 90 80 70 60 1/QN ( (Qj-Q(j-1) * log (t-t(j-1) ) ) 50 3 4 5 6 7 8 50 40 30 20 Injectivity test. ASAL4 800 750 700 650 600 Multirate drawdown. ASAL6 10 Time sec 0 100 1000 10000 550 1/QN ( (Qj - Q(j-1) * log (( t - t(j-1)) 500 5.8 5.9 6 6.1 6.2 6.3 6.4
HYDRODYNAMIC PROPERTIES OF THE DEEP RESERVOIR IN ASAL RIFT ZONE ASAL3 Drawdown tests ASAL4 injectivity test Semilog Bilog Semilog Bilog Wt ton/h Q ton/h kh dm skin kh dm 79-130 51 15.6-5 15.6 Multiple 15.9 155-225 70 15.7 5.7 225-300 75 6-5 - 5 16 6 300-357 57 13.4-5 13.4 ASAL3 recovery tests Wt ton/h Q ton/h kh dm 357-0 357 7.3 87-0 87 5.8 Q m3/h kh dm kh dm Injectivity 70 0.6 0.7 After injection 0.28 ASAL6 Drawdown tests Wt ton/h Q ton/h Semilog kh dm Multiple 4.11 Multiple 6.4 skin Bilog kh dm 65.2-78.3 13.1 6.9 10 3.7
Pression à 1100 PRESSURE BUILD-UP MEASUREMENTS. ASAL3 82 81 80 79 78 77 76 75 ( ta + tp ) / ta 74 1 10 100 1000 10000 100000 Build-up décembre 1987 Build-up mars 1990
DEEP RESERVOIR RESULTS IN ASAL Reservoir recognized in ASAL1, ASAL3 and ASAL 6 (in the same area) Temperature 260 C to 280 C Reservoir: Dalha basalts (9-4 My), 1050 m to 1300 m ASAL 3 production: Initial characteristics: total mass flow 360 t/h for 12.5 WHP Kh: 6.3 dm TDS in the reservoir: 116 000 ppm Scaling in the well (6 to 10 mm): sulphides (PbS, ZnS) Scaling in surface equipment: amorphous Si with Fe and Mn Severe decrease of production rate Decrease of bottom hole pressure ASAL INTERMEDIATE RESERVOIR Recognized in all Asal geothermal wells but not yet studied Reservoir: Top of Stratoid series and the bottom of Asal series Located between 300 m and 600 m Temperature 130 C to 190 C TDS : 50 g/l
ARTA (GEOTHERMICA 1982)
NORD-GOUBHET (BRGM 1983)
LAKE ABHE GEOTHERMAL PROSPECTS
OBOCK GEOTHERMAL PROSPECTS
GROUNDWATER THERMAL ANOMALIES DJIBOUTI AQUIFER
CONCLUSIONS HANLE-GAGGADE BASINS ZONE Drilling results not conclusive in Hanle basin Exploration by drilling not completed Need for new geophysical surveys as EM, AMT Reevaluate possibility of new drillings ASAL RIFT ZONE Deep reservoir of high enthalpy demonstrated in ASAL1 area Lateral extension of deep reservoir not yet evident Permeability and circulations controlled by fractures Major problem of scaling still to be resolved Geophysical surveys describe complex structures of reservoirs Fairly good understanding of fluid origin based on geochemistry and isotopes Shallow reservoir with medium enthalpy are preliminary and significant results The shallow reservoir is likely to have good extension
PERSPECTIVES FOR GEOTHERMAL DEVELOPMENT ASAL RIFT ZONE Realize exploration with drilling in the shallow reservoir Develop both reservoirs for electricity production OBOCK ZONE Realize geophysical surveys with EM and AMT methods Realize geochemical and isotopic studies on the hydrothermal manifestations Exploration drilling Feasibility study LAKE ABHE AND GAGGADE ZONES Realize geophysical surveys with EM and AMT methods Realize geochemical and isotopic studies on the hydrothermal manifestations Exploration drilling Feasibility study NORTH REGIONS OF ASAL LAKE
Thank you CERD