CONCEPTUAL MODEL OF THE ALUTO-LANGANO...
Transcript of CONCEPTUAL MODEL OF THE ALUTO-LANGANO...
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TRAINING ON SURFACE EXPLORATION STUDIES FOR GEOTHERMAL RESOURCES AND DEVELOPMENT OF CONCEPTUAL MODELS
UNDER THE AUSPICES OF INTERIM PROJECT COORDINATION UNIT OF THE AFRICA GEOTHERMAL CENTER OF EXCELLENCE
CONCEPTUAL MODEL OF THE ALUTO-LANGANO GEOTHERMAL
SYSTEM, ETHIOPIA
MESERET T. ZEMEDKUN
UN ENVIRONMENT
ETHIOPIA
• Ethiopia has actively been exploring for its geothermal resources since 1969
• Over 23 high temperature geothermal potential areas identified and only two geothermal prospects are subjected for drilling.
• Estimated potential of more than 10,000 MWe
• A larger number of areas have potential for medium to low temperature resources throughout the Ethiopian Rift System.
ALUTO - LANGANO
TENDAHO
TWO GEOTHERMAL FIELDS SUBJECTED FOR DRILLING
Aluto-Langano Field
• Drilling commenced in 1981 where a total of eight deep exploration wells were drilled.
• Four wells found to be productive with a max. temp. of 300 C.
• The 7.2 MWe Geothermal Combined Cycle Unit was commissioned in 1998.
• The plant had intermittent operation between 1998 and 2014 with challenges of maintenance
Ethiopia - Aluto− Drilling is in preparation to allow for
expansion of the field for 70 MWe
− Financing for drilling is from World
Bank, Iceland, JICA and Government of
Ethiopia
− Two wells were drilled between 2013
and 2015 (LA-9 &10)
− Progress has slowed since 2015 due to
various challenges
Legend Geological Mapping
1:50,000 scale
• LITHOLOGICAL AND
STRUCTURAL STUDIES
•HEAT SOURCE
Abundant silicic volcanoes,
recent volcanic products
•PERMEABILITY
WFB and other transverse
faults (production of
secondary Permeability)
GSE, 2018
W E
Total Alkali-Silica diagram for classification of
Aluto outcropping rocks.
SURACE MANIFESTATIONS
SOIL GAS AND TEMPERATURE ( 400 Radon and 200 CO2)
Consultancy Services for Geothermal Surface Exploration in Aluto Langano - Ethiopia
Classed post map of the activity of 222Rn in soil gases for the 430 stations surveyed during this work
Classed post map of soil temperature measured at 1 m depth in the 375 stations surveyed during this work
Areas of high CO2 fluxes are situated: (i)
along the Jawe fault zone and (ii) at Bobessa
and about 1.5 km to the south of it.
Soil temperature anomalies accompanied by CO2 flux anomalies
Geochemical Study ( Fluid, gas, isotopic, Radon, Co2 flux)
GSE, 2018
Geochemical Study ( Fluid, gas, isotope, Radon, Co2 flux)
Location map of the deep geothermal wells (greensymbols), Temperature gradient wells (whitesymbols), and surface manifestations of the Aluto-Langano geothermal field, including bothfumaroles and steaming grounds (yellow symbols)
GSE, 2018
Cl
SO4 HCO3
0 25 50 75 100
25
50
75
100
0
0
25
50
100
75
Figure 12A. Cl - HCO3 -SO4 PLOT (2003)
Bole SP
SP-84
SP-2
TG-31
TG-32
Shalla NE
Shalla SW
Chitu Sp
Wondo (Belle)
Wondo (Giorgis)
Water Classification
A-C BICARBONATE
Q
K/100Sqrt Mg
0 25 50 75 100
Figure 13A. Evaluation of Na-K-Mg temperatures (1973-2003). After Giggenbach (1988)
25
50
75
100
0
0
25
50
100
75
Na/1000
immature waters
80
100
120140160
180200
220
240
260
280
300
320340
Bole Sp
SP-84
SP-2
TG-32
TG-31
Shalla (SW)
Chitu HS
Wondo (Giorgis)
Wondo (Belle)
Evaluation of Na-K-Mg temperatures
• Geophysical Investigations with emphasis to
parameters that are sensitive to temperature
and fluid content of the Rocks ( gravity,
Magneto telluric and Microseismic Survey).
• GRAVITY Used to provide information on
subsurface structures and intrusive bodies
• Resistivity Methods Used to Map low resistivity
of the areas Abundance and distribution of
hydrothermal clay over active systems is used
to delineate the target areas
• Cap rock, normaly smectite clay ( Low
resitivity) The underlining reservoir ( Chlorite
clay) higher resistivity
Geophysical Study: MT-TEM, Gravity and Microseismic survey
GEOPHYSICS
• ELECTRICAL RESISTIVITY
•MAGNETICS
•GRAVITY
• MICROSEISMIC
• TG WELLS WERE DRILLED
MT SURVEY: 1D INVERSE MODELLING
Consultancy Services for Geothermal Surface Exploration in Aluto Langano - Ethiopia
In order to have a better picture of the clay cap distribution, all the
1D smooth models were interpolated with a three-dimensional
gridding software to obtain a 3D pseudo model of the resistivity
distribution. The 20 Ohm m resistivity surface was then
extrapolated, assuming that it can delineate the clay cap
distribution, and three maps were elaborated
Elevation a.s.l. of the bottom of the clay cap, assumed to becoincident with iso-resistive surface 20 Ohm m
➢ Bottom Elevation of the Clay Cap:
The bottom of the clay cap shows three
discontinuities (dashed white lines), that delineate
a region of up-doming labelled D1. This region
well correlates with the isotherm updoming
detected in wells LA-03 to LA-08. A second region
of updoming labelled D2 is imaged in the plain
west of the AVC
Geophysical Study: MT
GSE, 2018
West-east 2D resistivity profiles
Geophysical Study: MT
GSE, 2018
Negative anomaly N3. It extends over the south-
eastern lower portion of the AVC, mostly in
pumiceous pyroclastic products of both pre-
calderic and syn-post-calderic age. Recent rhyolite
lava flows outcrop to the west and north of the
anomaly. Similarly to anomaly N1, here too many
crateric structures are developed within the
anomaly
Residual Bouguer Anomaly Map at 2,560 kg/m3
Negative anomaly N4. It is located in
correspondence of the alluvial deposits which
occupy the very center of the caldera
Positive anomaly P1. It extends in the eastern
part of the caldera, being centered around a
volcanic edifice of post-caldera rhyolitic lava
flows
Gravity
GSE, 2018
HORIZONTAL DERIVATIVES
The gradient map shows rectilinear
features L1, L2 and L3, trending NNE-
SSW and reflecting the faults of the
Wonji system, which crosses the whole
AVC: in particular, L1 corresponds to the
Worbota-Adonsha lineament, L2 to the
Artu Jawe-Oitu Artu lineament and L3 to
the Bobessa-Gebiba lineament
(although slightly displaced to the east).
Rectilinear features L4 and L5, have,
NNW-SSE trend
Horizontal gradient magnitude
Geophysical Study: Gravity
ANALYSIS OF THE RESULTS
Due to the low number of registered events, for a better reconstruction of the seismological setting the
ALMS data were combined with the data collected in 2012-2014 by the LMS
The Figures show the interpolation of hypocentral depths greater than 2 km b.g.l. It can be observed
that the interpolation suggests the existence of a dome-like structure reaching its top at a depth of
about 5 km b.g.l. and slightly displaced to the east in relation with the centre of the caldera
Interpolation of depth events, of integrated ALMS+LMS catalogue, greaterthan 2 km depth. Left: SN section, Right: WE section. The dashed blacklines are the projected caldera rims
Geophysical Study, Microseismic
ANALYSIS OF THE RESULTS
Aluto, Geophysical Study: MT, Gravity and Microseismics
W-E Cross Section 1 of 10
ALUTO-VOLCANIC PRODUCTS
Lake sediments
Bofa basalt
Tertiary ignimbrite
GSE, 2018
FURTHER INFORMATION FROM THE DRILLED WELLS
LA-3
INFORMATION FROM THE DRILLED WELLS TO DEVELOP CONCEPTUAL MODEL
0 50 100 150 200 250 300 350
Temperature (°C)
-500
0
500
1000
1500
2000
Ele
vatio
n(m
.a.s
.l)
Legend
LA1-T16
LA2-T13
LA3-T55
LA4-T33
LA5-T18
LA6-T15
LA7-T27
LA8-T10
Figure 1: Downhole Temperature Profiles (Aluto wells)
File:Tempelveation
1
(
⊥ ⊥ ⊥ ⊥
0 1 2 3 Km
Lake Ziway
LA-7LA-6
LA-4
LA-8
LA-3
LA-5
LA-1
Lake Langano
LA-2
DOWNHOLE TEMPERATURE PROFILES
CLAY MINERAL STUDIES
Distribution of clay minerals with temperature
Mixed Layer Illite smectite
Illite-chlorite
illite
chlorite
Chlorite intergrade
Chlorite intergrade
FLUID CHEMISTRY
GEOCHEMISTRY
• Water and gas sampling from thermal
manifestations and the wells
•Analyse for major cations and anions
•Data processing using various geochemical
softwares (e.g. WATCH, SOLMINEQ 88 etc..)
•Determine the reservoir temperature using various
chemical geothermomters (e.g. Si-geothermometer,
Na-k, Na-K-Ca geothermometers)
AASGC
Cl
SO4HCO3
0 25 50 75 100
FIGURE 2: A plot of Cl-HCO3-SO4.
LA-6 (1985-2000)
LA-3 (1985-2000)
FLUID CHEMISTRY
120 160 200 240 280 320 Temperature ( C)
-0.80
-0.40
0.00
0.40
0.80
1.20
S a t u r a t i o n I n d e x ( S I ) Quartz
Amorphous silica
Calcite
FIGURE 6: A plot of SI vs temperature (well LA-3)
80 120 160 200 240Temperature ( C)
-0.80
-0.40
0.00
0.40
0.80
1.20
S
atur
atio
n In
dex
(SI)
Quartz
Calcite
Amorphous silica
FIGURE 8: A plot of SI vs temperature (well LA-4)
SATURATION INDICES OF MINERALS
FLUID INCLUSION GEOTHERMOMETRY
CHAIXMECA H-F STAGE
V-RICH INC
P-INCLUSIONE
S-INCLUSIONE
TYPES OF INCLUSIONS
THE ALUTO-LANGANO GEOTHERMAL FIELD
M.T
LA-7
THE ALUTO-LANGANO GEOTHERMAL FIELD
Interpretation of Fluid inclusion Results
M.T
LA-7
Mixed Layer Illite smectite
Illite-chlorite
illite
chlorite
Chlorite intergradeChlorite intergrade
Distribution of clay minerals vs temperature
The Aluto-Langano Geothermal field, Ethiopia
THE ALUTO-LANGANO
GEOTHERMAL FIELD
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BOBESA to be explored by
drilling in parallel with Aluto
for additional 35 MW
3 well sites are selected
within 5 sq km area
Main Reasons
1. Shallower depth
2. Better permeability
3. Upflow zone
4. Potential 35 MW
Conceptual modelling, Aluto Integrated results
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The areal extent of the reservoir is inferred on the base of the geoelectrical anomaly
Top of reservoir is expected at shallow depth 600m
thickness of the reservoir is assumed to amount to 1,200 m.
The reservoir is expected to be two-phase in the upflow zone and liquid dominated in the peripheral one
Conceptual modelling, Aluto, Integerated results
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