The KarahaTelaga Bodas Geothermal System, Indonesia

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The Karaha-Telaga Bodas Geothermal System,
Indonesia
Joe Moore Energy Geoscience Institute
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Location Map of Karaha-Telaga Bodas
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1982 Eruption of Galunggung Volcano
Photo by J. Lockwood, 1982
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Kawah Galunggung
Photo by J. Lockwood, 1982
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View of Kawah Saat and Telaga Bodas
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Locations of Wells and Thermal Features at
Karaha-Telaga Bodas
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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
• Chemical sampling of springs, fumaroles and non
  thermal waters
• Interpretation of aerial photographs
• New MT surveys
• Reassesment of existing geophysical data
• Drilling of core and production wells

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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 150000

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Geologic Results

• Andesitic to Basaltic stratovolcano. Epiclastic
  and pyroclastic deposits dominate lava flows
  less abundant intrusive rocks occur at depths of
  lt3 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 lt6000 years
  old.

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Lineament Map

Geothermex
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Geochemical Surveys

• Spring and fumaroles were sampled for major and
  minor elements, oxygen and deuterium isotopes and
  3He/4He

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Geochemical Results

• Discharges occur at two widely separated
  locations, at Telaga Bodas/Kawah Saat and Kawah
  Karaha.
• Springs (all non boiling)
• Telaga Bodas (Tlt145oF) acidic Cl-SO4 waters
• Karaha are dilute, cool (lt100oF) neutral pH and
  bicarbonate rich
• Outlying areas dominantly bicarbonate- rich
  (Tlt150oF)
• SO2 found in TLG2-1 and high F in T-2. Native S
  is present at Telaga Bodas
• Most springs discharge mixed cation - HCO3
  waters.
• No surface discharges indicative of a deep NaCl
  reservoir were found
• 3He/4He ranges from 7.1-7.7 Ra in concession
  5.1-5.9 Ra outside

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Telaga Bodas Water Composition(mg/l)
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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
• Microearthquake Survey
• Natural seismic activity recorded by 5
  seismographs in Karaha area
• 95 day monitoring period
• Resistivity, gravity and microearthquake data
  collected in 1980s, reprocessed in 1996-97

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MT Station Locations

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Locations of Survey Sites Near Telaga Bodas
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MT Model of Low-Resistivity Conductor
(Raharjo et al, 2002)
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(Raharjo et al., 2002)
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Schlumberger Apparent Resistivity
RESULTS 1) A well developed low near Telaga
Bodas (lt5 ohm-m) 2) 7 ohm-m contour encloses
surface features in vicinity 3) A weak low (gt15
ohm-m) is located near Karaha Karaha

AB/2 1000 m
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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)

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East-West Gravity Profile Of Karaha-Telaga Bodas
(Raharjo et al., 2002)
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Microearthquake Survey

• 200 events (83 between .2 to 2.4) were recorded
• 73 centered south of the fumarole field 10 to
  the north

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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 1998.
• Well temperatures and pressures were measured and
  the compositions of the discharged fluids
  determined.
• The project is currently inactive.

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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 low-resistivity
  conductor extending from Kawah Karaha to Telaga
  Bodas and a positive gravity anomaly near Telaga
  Bodas. The electrical data suggest the presence
  of an extensive geothermal system beneath the
  volcanic ridge.

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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.

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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.

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• 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 produce near neutral waters.

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• 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.

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THE END