Effect of Magnetotellurics DataDensity in Geothermal Resource           Exploration          Mehran Gharibi         Quante...
Outline:•   Objectives•   Introduction to Magnetotelluric (MT) Method•   Titan-24 and Spartan MT measurements•   MT in Geo...
Objectives:Investigate resolution and reliability of the 3D MTresistivity models in terms of the data density usedin inver...
Magneto-Telluric (MT) Method• The MT is a frequency-domain natural-field EM geophysical  method   – frequency range 10000 ...
MT measurementsSchematic of simultaneous measurement of plane-wave electromagneticfield fluctuations in five components: E...
Calibration Chamber for Magnetic Sensors3-layer passive shielded and active                                               ...
Spartan MT acquisition                                Acquisition system                                • Full tensor MT  ...
Titan-24 MT Acquisition     Typical        2 Channel     Station           AM     Set-up                                  ...
MT Method in Geothermal Explorations:• MT data are used to produce electrical resistivity distributionof the subsurface• E...
Interpretation of the MT Data                ⎛ 0        Z⎞   ⎛ 0     Z xy ⎞   ⎛ Z xx   Z xy ⎞• Data          ⎜            ...
Spartan MT Field Survey• Large scale MT survey over a geothermal resource area• More than 160 MT sites• Site spacing betwe...
MT survey location Map  3D inversion area      2D cross-sections
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 tim...
3-D Inversion – 5 Frequencies    Surface = 0 m                                     Conductive                             ...
3-D Inversion – 5 Frequencies    Surface = -1300 m                                      Conductive                        ...
3-D Inversion – 5 Frequencies    Surface = -2000 m                         Anomaly or                          Artifact !?...
3-D Inversion – 5 Frequencies    Surface = -3000 m                         Anomaly or                          Artifact !?...
3-D Inversion – 5 Frequencies             Selected Cross-sections                                        Conductive       ...
3-D InversionsThe original frequency band is decimated for the 3-D inversions                  18 Frequencies (3 per decad...
3-D Inversion – 18 Frequencies•   # of frequency per site: 18•   # of sites: 162•   # of Mesh: 25 x 41 x 18•   Inversion t...
3-D Inversion – 18 Frequencies    Surface = 0 m                                     Conductive                            ...
3-D Inversion – 18 Frequencies    Surface = -1300 m                                      Conductive                       ...
3-D Inversion – 18 Frequencies    Surface = -2000 m                             No Artifact !                        Geoth...
18 Frequencies    Selected Cross-sections     5 Frequencies    Interpreted                             Interpreted    Geot...
Summary•    Geothermal fields and resources can efficiently be mapped     and characterized using MT measurements.•     3-...
Thank You        Toronto, CanadaReno, USA   Hermosillo, Mexico                                                            ...
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Building, Owning & Operating an Independent Power Producer Business in Turkey by Implementing an Innovative Power Cycle Technology.

  1. 1. Effect of Magnetotellurics DataDensity in Geothermal Resource Exploration Mehran Gharibi Quantec Geoscience GeoPower, Turkey 2011
  2. 2. Outline:• Objectives• Introduction to Magnetotelluric (MT) Method• Titan-24 and Spartan MT measurements• MT in Geothermal Exploration• 3D Inversion and Interpretation• Summary
  3. 3. Objectives:Investigate resolution and reliability of the 3D MTresistivity models in terms of the data density usedin inversion; i.e. Resolution vs. Frequency density.
  4. 4. 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 earths electrical resistivity structure – from nearly the surface to several tens of km.
  5. 5. MT measurementsSchematic of simultaneous measurement of plane-wave electromagneticfield fluctuations in five components: Ex, Ey, Hx, Hy and Hz Ground surface Electric field dipoles Ex Ey Hz Hy Hx Magnetic field sensors ⎛ E x ⎞ ⎛ Z xx Z xy ⎞⎛ H x ⎞ Apparent Resistivity of ⎜ ⎟=⎜ ⎟⎜ ⎟ Calculate Inversion ⎜E ⎟ ⎜Z Z yy ⎟⎜ H y ⎟ Resistivity Subsurface ⎝ y ⎠ ⎝ yx ⎠⎝ ⎠
  6. 6. Calibration Chamber for Magnetic Sensors3-layer passive shielded and active Active-Fieldfield cancellation calibration room Cancellation FrameSolenoid Magnetic Passive Active Frequency Sheilding Sheilding coil sensor (Hz) Factor Factor 4m 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 3-layer Passive Magnetically 0.01 10 1,000 Shielded Room
  7. 7. Spartan MT acquisition Acquisition system • Full tensor MT • 24-bit resolution • Automatic data acquisition • Remote reference processingField setup• Man portable• Coils buried• Flexible spacing• Low environmental footprint
  8. 8. Titan-24 MT Acquisition Typical 2 Channel Station AM Set-up • Full tensor MT • 24-bit resolution Battery • High spatial site density • DC-IP acquisition capability 2400m current electrode (mobile) cross-line potential electrode (fixed) cross- 50m in-line potential electrode (fixed) in- 100m Bx infinity current electrode (fixed) By 100m 2 channel AM >10 km Base magnetometer Site 1 channel AMLAN Link to Logging Truck Line Length - 2400 m 24 E x 100m dipoles 12 E y 100m dipoles 25 current stations 2 Bx/B y magnetometer sites >20 km Bx By Remote Magnetometer site 8
  9. 9. MT Method in Geothermal Explorations:• MT data are used to produce electrical resistivity distributionof 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 definedand controlled by a combination of the above factors.• Resistivity signature associated with the geothermal system isused to detect/map/characterize the reservoir
  10. 10. Interpretation of the MT Data ⎛ 0 Z⎞ ⎛ 0 Z xy ⎞ ⎛ Z xx Z xy ⎞• Data ⎜ ⎜− Z ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ 0⎟ ⎠ ⎜Z ⎝ yx 0 ⎟ ⎠ ⎜Z ⎝ yx Z yy ⎟ ⎠ ρ ρxy, ρyx• Inversion 1-D 2-D 3-D• Resistivity Model
  11. 11. 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.
  12. 12. MT survey location Map 3D inversion area 2D cross-sections
  13. 13. 3-D InversionsThe original frequency band is decimated for the 3-D inversions 5 Frequencies (1 per decade) Original Decimated
  14. 14. 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
  15. 15. 3-D Inversion – 5 Frequencies Surface = 0 m Conductive Cap Resistive Core Interpreted Geothermal System
  16. 16. 3-D Inversion – 5 Frequencies Surface = -1300 m Conductive Cap Resistive Core Interpreted Geothermal System
  17. 17. 3-D Inversion – 5 Frequencies Surface = -2000 m Anomaly or Artifact !? Interpreted Geothermal System
  18. 18. 3-D Inversion – 5 Frequencies Surface = -3000 m Anomaly or Artifact !? Interpreted Geothermal System
  19. 19. 3-D Inversion – 5 Frequencies Selected Cross-sections Conductive Resistive Cap Core Interpreted Geothermal System
  20. 20. 3-D InversionsThe original frequency band is decimated for the 3-D inversions 18 Frequencies (3 per decade) Original Decimated
  21. 21. 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
  22. 22. 3-D Inversion – 18 Frequencies Surface = 0 m Conductive Cap Resistive Core Interpreted Geothermal System
  23. 23. 3-D Inversion – 18 Frequencies Surface = -1300 m Conductive Cap Resistive Core Interpreted Geothermal System
  24. 24. 3-D Inversion – 18 Frequencies Surface = -2000 m No Artifact ! Geothermal reservoir!?
  25. 25. 18 Frequencies Selected Cross-sections 5 Frequencies Interpreted Interpreted Geothermal Geothermal System System
  26. 26. 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).
  27. 27. Thank You Toronto, CanadaReno, USA Hermosillo, Mexico Mumbai, India Arequipa, Peru Goiania, Brazil Lobatse, Botswana Santiago, Chile Mendoza, Argentina Brisbane, Australia www.quantecgeoscience.com

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