The Karaha-Telaga Bodas Geothermal
System, Indonesia
Joe Moore
Energy & Geoscience Institute
Location Map of Karaha-Telaga Bodas
Photo by J. Lockwood, 1982
1982 Eruption of
Galunggung Volcano
Photo by J. Lockwood, 1982
Kawah Galunggung
View of Kawah Saat and Telaga Bodas
Exploration History
In 1980s, Pertamina drilled 4 shallow
gradient holes and conducted MT,
resistivity, gravity and microearthquake
surveys.
KBC initiated an aggressive 2 1/2 year
program in Dec. 1994 that included:
1. Chemical sampling of springs, fumaroles
and non thermal waters;
2. Interpretation of aerial photographs
3. New MT surveys
Geologic Studies
• Extensive cover precluded detailed
geologic mapping
• Existing geologic maps and available
whole-rock ages were compiled.
• Lineaments were mapped using aerial
photographs at a scale of 1:50000
Geologic Results
• Andesitic to Basaltic stratovolcano.
Epiclastic and pyroclastic deposits
dominate; lava flows less abundant;
intrusive rocks occur at depths of <~3 km.
• K-Ar ages of surface rocks range from
1.75 to .32 Ma. Flank collapse of Kawah
Galunggung occurred at 4200 years BP.
subsequent 14C dating of well samples
indicates the system may be <6000 years
Lineament Map
Geothermex
Geochemical Surveys
Spring and
fumaroles were
sampled for major
and minor
elements, oxygen
and deuterium
isotopes and
3He/4He:
Geochemical Results
– Discharges occur at two widely separated
locations, at Telaga Bodas/Kawah Saat and
Kawah Karaha.
– Springs (all non boiling)
• Telaga Bodas: (T<145oF) acidic Cl-SO4 waters
• Karaha: are dilute, cool (<100oF) neutral pH and
bicarbonate rich
• Outlying areas: dominantly bicarbonate- rich
(T<150oF)
– SO2 found in TLG2-1 and high F in T-2.
Native S is present at Telaga Bodas
– Most springs discharge mixed cation - HCO3
Telaga Bodas Water Composition
(mg/l)
Lab pH
0.40
Mg
206
Na
K
SO4
Cl
SiO2
Fe
122
30
30500
8850
348
2320
Geophysical Surveys
• MT Surveys
1980s; broadly spaced stations (2-3 km
apart)
1996-97; 103 stations occupied in a 90 km2
area
• DC Resistivity (Slumberger Arrays)
214 locations at 500 m intervals along
several lines
covers western part of MT survey area
depth of penetration ~300 m
• Gravity Survey
regional survey across Karaha volcanic
massif
MT Station Locations
Locations of Survey Sites Near Telaga Bodas
MT Model of Low-Resistivity Conductor
(Raharjo et al, 2002)
MT Model of Low-Resistivity Conductor
(Raharjo et al, 2002)
(Raharjo et al., 2002)
Schlumberger Apparent
Resistivity
RESULTS
1) A well developed low near
Telaga Bodas (<5 ohm-m)
2) 7 ohm-m contour encloses
surface features in vicinity
3) A weak low (>15 ohm-m) is
located near Karaha Karaha
AB/2 = 1000 m
Bouguer
Anomaly
Map
Data reduced
using density of
2.3 g/cc (GENZL)
North-trending
high follows ridge
axis
Circular gravity
high near Telaga
Bodas
Remodeled by
Tripp (2002),
Raharjo (2002)
East-West Gravity
Profile Of KarahaTelaga Bodas
(Raharjo et al., 2002)
Microearthquake Survey
200 events (83 between .2 to 2.4) were
recorded;
73 centered south of the fumarole field;
10 to the
north
Exploration and Drilling
History
9 core holes (877-2150
ft.) were drilled between
Nov. 1995 and May 1996.
First deep production test drilled in May 1996 at
Karaha fumaroles, based on thermal gradient
data.
From Sept. 1996 to Dec. 1997, 10 new core holes
(3340-6621 ft) and 7 deep production tests were
drilled.
Drilling of production wells continued until March
Key Results
• The surface manifestations consist of
fumaroles and springs reflecting boiling
and gas movement at depth. No springs
discharge water typical of a deep NaCl
reservoir.
• The resource may be vapor-dominated.
• Gas compositions indicate a magmatic
contribution to the fluids.
• Geophysical studies identified a lowresistivity conductor extending from
Kawah Karaha to Telaga Bodas and a
Key Results
•Early core holes provided good thermal data but were too
shallow to reach reservoir; later core holes were deeper
and provided reservoir information.
•Drilling success improved with time as data from core
holes was incorporated into the drilling program.
•The data do not define the limits of the geothermal
system. Eastern, southern and western boundaries are not
delineated.
What We Know Now
• Despite lack of thermal expressions, the
system is continuous beneath the volcanic
ridge from Telaga Bodas to Kawah
Karaha.
• The reservoir has the shape of a broad
arch.
• The conductive layer outlines, in a general
way, regions of high temperature. The
base of the conductive layer approximates
the base of the caprock.
• Telaga Bodas is the surface expression of
a magmatic vapor chimney.
• Heat is provided by young intrusions
emplaced during the last 6000 years.
• The deep fluid has low salinity, suggesting
meteoric waters are recharging the
geothermal system.
• Magmatic gases combined with extensive
drying out of the vapor zone lead to the
formation of acidic fluids in the southern
wells. The fluids are neutralized/diluted to
the north. Northern and central wells
• Pyroclastic rocks dominate the volcanic
section. Productive zones occur in
fractured pyroclastic rocks, lavas and
intrusives. Secondary permeability in the
pyroclastic deposits developed after the
rocks were altered and fractured. Rocks
with high primary porosities appear to be
minor contributors to the total fluid
production.
THE