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Geophysics for Geophysics for Geothermal ExplorationGeothermal Exploration

Dr. Hendra GrandisDr. Hendra GrandisGeofisika Geofisika -- ITBITB

AgendaAgenda

Basic concept of GeophysicsBasic concept of Geophysics: Review: Review

Geophysical signatures of a geothermal systemGeophysical signatures of a geothermal system

Geophysical methods for geotermal explorationGeophysical methods for geotermal exploration

ExamplesExamples

Discussion, Q/ADiscussion, Q/A

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Basic concepts of GeophysicsBasic concepts of Geophysics

Major task of geophysics is to make quantitative Major task of geophysics is to make quantitative statements about the interior of the earth statements about the interior of the earth ((modelmodel) from observation () from observation (datadata))

Data Data subsurface physical propertysubsurface physical property

Geophysical methods: Geophysical methods:

gravity, magnetics, geogravity, magnetics, geo--electrics, electrics, electromagnetics, seismics, ...electromagnetics, seismics, ...

data data processingprocessing

field field datadata

measurementmeasurement

signal / Earthsignal / Earth’’s Responses Response((observobserved ed parameterparameterss))

Basic concepts of GeophysicsBasic concepts of Geophysics

subsurface subsurface modelmodel

interpretainterpretattiionon

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Basic concepts of GeophysicsBasic concepts of Geophysics

Basic concepts of GeophysicsBasic concepts of Geophysics

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Elements of a geothermal systemElements of a geothermal system

Heat source Heat source (magmatic)(magmatic)

ReservoirReservoir

Cap rockCap rock

Recharge Recharge systemsystem

Isotherms

Smectite Clay

1 KM1:1

PropyliticAlteration in

FracturedGeothermalReservoir

Heat and Gasfrom Magma

Unaltered

BasinClays

ChlorideSpring

Acid SulphateFumarole

(Cumming Geoscience)

Role of GeophysicsRole of Geophysics

Role of geophysics is to identify each element of Role of geophysics is to identify each element of a geothermal systema geothermal system→→ geometrygeometry

→→ lithologylithology

→→ conceptual conceptual modelmodel

Isotherms

Smectite Clay

1 KM1:1

PropyliticAlteration in

FracturedGeothermalReservoir

Heat and Gasfrom Magma

Unaltered

BasinClays

ChlorideSpring

Acid SulphateFumarole

(Cumming Geoscience)

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Role of GeophysicsRole of Geophysics

Exploration of a geothermal system is a multiExploration of a geothermal system is a multi--disciplinary approachdisciplinary approach→→ Geology and GeochemistryGeology and Geochemistry→→ GeophysicsGeophysics→→ Drilling and Reservoir EngineeringDrilling and Reservoir Engineering

Geophysical signaturesGeophysical signatures

Gravity and magneticGravity and magneticss→→ grossgross--structure of a geothermal system structure of a geothermal system

(caldera / rim structure, pull(caldera / rim structure, pull--apart basin or apart basin or shear zone, etc.)shear zone, etc.)

→→ heat source (magmatic intrusion)heat source (magmatic intrusion)

GeoGeo--electricalelectrical→→ cap rockcap rock→→ reservoir zonereservoir zone

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Geophysical signaturesGeophysical signatures

SelfSelf--PotentialPotential→→ fluid movement (upfluid movement (up--flow, inflow, in--flow)flow)→→ fracture zonefracture zone→→ fluid movement (production, reinjection fluid movement (production, reinjection

process)process)monitoringmonitoring -- reservoir managementreservoir management

MicroMicro--seismicseismicss→→ fracture zonefracture zone→→ reservoir changesreservoir changes

Geophysical Techniques Geothermal ExplorationGeophysical Techniques Geothermal Exploration

Standard:Standard: MT, TMT, T--MT, TDEM, GravityMT, TDEM, Gravity

Legacy:Legacy: DipoleDipole--Dipole, Tensor DipoleDipole, Tensor Dipole--BipoleBipole

Special:Special: VES, AMT, CSAMT, SP, HEMVES, AMT, CSAMT, SP, HEMAeromagnetics, Precision Ground MagneAeromagnetics, Precision Ground Magneticstics

Research:Research: Reflection / Refraction SeismicReflection / Refraction SeismicSpecial ApplicationsSpecial Applications

Development:Development: Microgravity, Microearthquake, SubsidenceMicrogravity, Microearthquake, Subsidence

Proprietary:Proprietary: EE--Scan, EScan, E--Map Map

UnreviewedUnreviewed:: AquatrackAquatrack

Suspect:Suspect: Seismic Noise, Low Res Ground Magnetics Seismic Noise, Low Res Ground Magnetics Plausible methods with weak technical Plausible methods with weak technical supportsupport

(Cumming Geoscience)

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Problem / site specificProblem / site specific

Exploration strategyExploration strategy

→→ start with start with ““inexpensiveinexpensive”” or conventional or conventional methods to cover vast area methods to cover vast area (reconnaissance)(reconnaissance)

→→ delineate anomalous zonedelineate anomalous zone

→→ followfollow--up with specialized method for up with specialized method for detailed targetingdetailed targeting

GeophysicGeophysical Survey Designal Survey Design

Development strategyDevelopment strategy

→→ start from a specific area to a larger area, to start from a specific area to a larger area, to explore possibilities from existing (known) explore possibilities from existing (known) information information

GeophysicGeophysical Survey Designal Survey Design

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Typical Typical Geophysical Geophysical SurveySurveyss

Reconnaissance Reconnaissance →→ Gravity Gravity ((and magneticand magnetic))→→ GeoGeo--electrical electrical ResistivityResistivity Sounding and Sounding and

Mapping Mapping

Advanced Advanced →→ MagnetotelluricsMagnetotellurics (MT), Time Domain EM (MT), Time Domain EM

(TDEM)(TDEM)→→ MicroMicro--SeismicsSeismics

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Alteration Alteration –– Resistivity Resistivity

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transmitter generates time transmitter generates time varyingvarying EM fieldEM field

↓↓induces induces Eddy currentsEddy currents in the in the conductor (Earth)conductor (Earth)

↓↓generate secondarygenerate secondarymagnetic fieldmagnetic field

↓↓electric and magnetic fieldselectric and magnetic fieldsare sensed at the receiverare sensed at the receiver

Electromagnetic InductionElectromagnetic Induction

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natural natural electromagnetic fieldelectromagnetic field

MagnetotelluricsMagnetotellurics(MT)(MT)

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MT time seriesMT time series

1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3

PERIOD (sec.)

1E+0

1E+1

1E+2

1E+3

APP

. RES

ISTI

VITY

(Ohm

.m)

0

45

90

PHA

SE (d

eg.)

1E-3 1E-2 1E-1 1E+0 1E+1 1E+2 1E+3

PERIOD (sec.)

obs. data

calc. data

1E+0 1E+1 1E+2 1E+3

RESISTIVITY (Ohm.m)

1E+2

1E+3

1E+4

1E+5

DEP

TH (m

)

11--D MT smooth modelingD MT smooth modeling

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22--D and 3D and 3--D interpretation of MT data D interpretation of MT data in the in the BajawaBajawa geothermal field Flores, Indonesia geothermal field Flores, Indonesia (Uchida et al., 2002)(Uchida et al., 2002)

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22--D and 3D and 3--D interpretation of MT data D interpretation of MT data in the in the BajawaBajawa geothermal field Flores, geothermal field Flores, Indonesia (Uchida et al., 2002)Indonesia (Uchida et al., 2002)

KarahaKaraha--TelagaTelaga BodasBodas

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The The KarahaKaraha--TelagaTelaga BodasBodasGeothermal System, Indonesia Geothermal System, Indonesia ((RaharjoRaharjo et al., 2002)et al., 2002)

NorthNorth--trending high trending high follows ridge axisfollows ridge axis

Circular gravity high near Circular gravity high near TelagaTelaga BodasBodas

22--D D modellingmodelling

The The KarahaKaraha--TelagaTelaga BodasBodasGeothermal System, Indonesia Geothermal System, Indonesia ((RaharjoRaharjo et al., 2002)et al., 2002)

NorthNorth--trending high trending high follows ridge axisfollows ridge axis

Circular gravity high near Circular gravity high near TelagaTelaga BodasBodas

22--D D modellingmodelling

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The The KarahaKaraha--TelagaTelaga BodasBodasGeothermal System, Indonesia Geothermal System, Indonesia ((RaharjoRaharjo et al., 2002)et al., 2002)

The The KarahaKaraha--TelagaTelaga BodasBodasGeothermal System, Indonesia Geothermal System, Indonesia ((RaharjoRaharjo et al., 2002)et al., 2002)

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Repeat SP measurements at the Repeat SP measurements at the SumikawaSumikawa geothermal field, Japan geothermal field, Japan (Matsushima et al., WGC 2000)(Matsushima et al., WGC 2000)

Using surface SP to monitor underground fluid flow Using surface SP to monitor underground fluid flow -- an example from a an example from a HDR stimulation (HDR stimulation (DarnetDarnet et al., EAGE 64th Conference, 2002)et al., EAGE 64th Conference, 2002)

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SP monitoring during the hydraulic fracturing using the TGSP monitoring during the hydraulic fracturing using the TG--2 well 2 well (Kawakami & (Kawakami & TakasugiTakasugi, EAGE 56th Conference, 1994), EAGE 56th Conference, 1994)

Field setField set--up of Fluid Flow up of Fluid Flow Tomography, i.e. SP Tomography, i.e. SP monitoring integrated with monitoring integrated with misemise--àà--lala--massemasse (MAM) (MAM) measurementmeasurement

Reservoir monitoring by a Reservoir monitoring by a 44--D electrical technique D electrical technique (Ushijima et al., The (Ushijima et al., The Leading Edge, vol. 18 no. Leading Edge, vol. 18 no. 12, 1999)12, 1999)

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Hot dry rock (HDR) hydraulic Hot dry rock (HDR) hydraulic fracturing experiment, fracturing experiment, OgachiOgachiElectric Power Industry, Akita Electric Power Industry, Akita PerfecturePerfecture, Japan, Japan