Building, Owning & Operating an Independent Power Producer Business in Turkey by Implementing an...
-
Upload
suat-furkan-isik -
Category
Documents
-
view
172 -
download
1
description
Transcript of Building, Owning & Operating an Independent Power Producer Business in Turkey by Implementing an...
Effect of Magnetotellurics Data Density in Geothermal Resource
Exploration
Mehran GharibiQuantec Geoscience
GeoPower, Turkey 2011
Outline:
• Objectives
• Introduction to Magnetotelluric (MT) Method
• Titan-24 and Spartan MT measurements
• MT in Geothermal Exploration
• 3D Inversion and Interpretation
• Summary
Objectives:Investigate resolution and reliability of the 3D MT
resistivity models in terms of the data density used
in inversion; i.e. Resolution vs. Frequency density.
Magneto-Telluric (MT) Method• The MT is a frequency-domain natural-field EM geophysical
method – frequency range 10000 Hz - 0.001 Hz
• The method uses the earth’s EM natural time variations
- Lower Frequencies ( < 1 Hz): Ionospheric; initiated by interaction of the solar wind with the earth’s magnetic field.
- Higher Frequencies ( > 1 Hz): Atmospheric; initiated by global lightning activities.
• Image the earth's electrical resistivity structure – from nearly the surface to several tens of km.
MT measurements
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛=⎟⎟
⎠
⎞⎜⎜⎝
⎛
y
x
yyyx
xyxx
y
x
HH
ZZZZ
EE Apparent
ResistivityResistivity of SubsurfaceCalculate Inversion
Ey
Ex
HyHz
Hx
Schematic of simultaneous measurement of plane-wave electromagnetic field fluctuations in five components: Ex, Ey, Hx, Hy and Hz
Electric field dipoles
Magnetic field sensors
Ground surface
Calibration Chamber for Magnetic Sensors3-layer passive shielded and active field cancellation calibration room
Frequency (Hz)
Passive Sheilding
Factor
Active Sheilding
Factor
10K 100,000 100,000
1K 50,000 50,000
100 2,000 2,000
10 100 1,000
1 50 1,000
0.1 20 1,000
0.01 10 1,000
3-layer Passive Magnetically
Shielded Room
Active-Field Cancellation
Frame
4 m
Solenoid coil
Magnetic sensor
Spartan MT acquisition
Field setup • Man portable• Coils buried• Flexible spacing• Low environmental footprint
Acquisition system • Full tensor MT• 24-bit resolution• Automatic data acquisition• Remote reference processing
8
Line Length - 2400 m24 Ex 100m dipoles12 Ey 100m dipoles25 current stations2 Bx/By magnetometer sites
current electrode (mobile)current electrode (mobile)
100m
crosscross--line potential electrode (fixed)line potential electrode (fixed)
2400m
inin--line potential electrode (fixed)line potential electrode (fixed)
2 channel AM2 channel AM
1 channel AM1 channel AM
BxBy
2 ChannelAM
Battery
TypicalStationSet-up
BxBy
RemoteRemoteMagnetometerMagnetometer
sitesite
>20 km
Base magnetometer SiteBase magnetometer SiteLAN Link to Logging Truck
50m
infinity current electrode (fixed)infinity current electrode (fixed)>10 km
100m
Titan-24 MT Acquisition• Full tensor MT• 24-bit resolution• High spatial site density• DC-IP acquisition capability
MT Method in Geothermal Explorations:
• MT data are used to produce electrical resistivity distribution of the subsurface
• Electrical resistivity is a function of;• solid matrix - geological formation and alteration• pore fluids - chemistry and salinity• porosity – geological fissure and fracture• temperature
• A geothermal system or a hydrothermal reservoir is defined and controlled by a combination of the above factors.
• Resistivity signature associated with the geothermal system is used to detect/map/characterize the reservoir
Interpretation of the MT Data
• Data
• Inversion
• ResistivityModel
⎟⎟⎠
⎞⎜⎜⎝
⎛− 00Z
Z⎟⎟⎠
⎞⎜⎜⎝
⎛0
0
yx
xy
ZZ
⎟⎟⎠
⎞⎜⎜⎝
⎛
yyyx
xyxx
ZZZZ
1-D 2-D 3-D
ρ ρxy, ρyx
Spartan MT Field Survey
• Large scale MT survey over a geothermal resource area
• More than 160 MT sites
• Site spacing between 500 m and 1000 m
• Frequency range 250 Hz – 0.001 Hz
• Objective is to identify an exploration drilling location
• Geothermal reservoir target at >1500 m
• Interpretation based on 3-D with different number of frequencies.
MT survey location Map
3D inversion area 2D cross-sections
Original Decimated
3-D InversionsThe original frequency band is decimated for the 3-D inversions
5 Frequencies (1 per decade)
3-D Inversion – 5 Frequencies• # of frequency per site: 5• # of sites: 162• # of Mesh: 25 x 41 x 18• Inversion time: 602 hours• Hardware: 2 x CPU processor with 4 GB RAM
4 km
3-D Inversion – 5 Frequencies
Interpreted Geothermal
System
ResistiveCore
ConductiveCap
Surface = 0 m
3-D Inversion – 5 Frequencies
Interpreted Geothermal
System
ResistiveCore
ConductiveCap
Surface = -1300 m
3-D Inversion – 5 Frequencies
Interpreted Geothermal
System
Anomaly orArtifact !?
Surface = -2000 m
3-D Inversion – 5 Frequencies
Interpreted Geothermal
System
Anomaly orArtifact !?
Surface = -3000 m
Selected Cross-sections
Interpreted Geothermal
System
ResistiveCore
ConductiveCap
3-D Inversion – 5 Frequencies
3-D InversionsThe original frequency band is decimated for the 3-D inversions
18 Frequencies (3 per decade)
Original Decimated
3-D Inversion – 18 Frequencies• # of frequency per site: 18• # of sites: 162• # of Mesh: 25 x 41 x 18• Inversion time: 552 hours• Hardware: 2 x 4 CPU processor with 24 GB RAM
4 km
3-D Inversion – 18 Frequencies
Interpreted Geothermal
System
ResistiveCore
ConductiveCap
Surface = 0 m
3-D Inversion – 18 Frequencies
Interpreted Geothermal
System
ResistiveCore
ConductiveCap
Surface = -1300 m
3-D Inversion – 18 Frequencies
No Artifact !Geothermal reservoir!?
Surface = -2000 m
Selected Cross-sections
Interpreted Geothermal
System
Interpreted Geothermal
System
18 Frequencies 5 Frequencies
Summary
• Geothermal fields and resources can efficiently be mapped and characterized using MT measurements.
• 3-D inversions are computationally expensive;- a subset of the dataset with 3 frequencies/decade
would be sufficient to produce the resistivity distribution of the subsurface while minimizing the artifacts
• Development in 3D inversion;- Parallel computing of the 3-D MT inversion using
cluster of high performance CPUs (e.g. 48 CPUs and 64 GB RAM)
- It speeds up the inversion process several times (5-10 times).
Thank You
Arequipa, Peru
Reno, USA
Toronto, Canada
Lobatse, BotswanaSantiago, Chile
Mendoza, Argentina
Hermosillo, Mexico
Goiania, Brazil
Mumbai, India
Brisbane, Australia
www.quantecgeoscience.com