Geothermal Resource Exploration
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This document summarizes a magnetotelluric (MT) survey conducted in Denizli, Turkey to explore the geothermal potential of the region. The survey involved collecting high quality MT data from 92 sites using Spartan MT data loggers. The data was inverted in 3D using WSINV3DMT, producing resistivity models of the subsurface down to 3000 meters depth. The models image the sedimentary fill of the Denizli graben and the underlying bedrock, helping to identify potential geothermal reservoirs and determine well locations to reduce drilling risks. The MT survey was able to map subsurface resistivity variations despite the industrialized nature of the area, demonstrating the effectiveness of MT for geothermal exploration.
Geothermal Resource Exploration
- 3. Quantec Geoscience Limited is a world leader in non-seismic ground geophysical exploration with worldwide offices since 1986. Quantec offers state-of-the-art Deep Earth Imaging Technologies thru our proprietary Orion 3D, Titan 24 DCIP&MT and Spartan MT data acquisition, processing and interpretation, as well as the full suite of conventional EM survey methods. Toronto, Canada Reno, USA Hermosillo, Mexico QIPS, Barbados Arequipa, Peru Santiago, Chile Lobatse, Botswana Mendoza, Argentina Brisbane, Australia www.quantecgeoscience.com
- 7. Magnetic Field Sensors Coil Calibration Chamber • Quantec owns and employs a calibration room for calibrating magnetic field sensors. • The room provides both 3-layer passive shielding and active field cancellation. • Each individual magnetic coil is calibrated before deployment to the field and coil calibration constants are archived for each and every job. • Only two facilities of its kind in the world.
- 9. MT Signal Sources Lower Frequencies: f < 1 Hz Interaction of the solar wind with the earth’s magnetic field NASA E(ω ) = Z(ω )B(ω ) Higher Frequencies: f > 1 Hz Global lightning activities Thunderstorms
- 10. NASA
- 12. MT Signal Sources • Sunspot activity has 11 year period. • Last solar maximum was in 2001. • Past few years were tough for MT acquisition especially at high noise areas.
- 13. Penetration Depth (Skin Depth) δ = 503 ρT δ = 503 100Ωm × 4s δ = 10060 m ~ 10 km ~ 100Ωm f = 10 Hz ⇒ δ = 1.6km f = 40 Hz ⇒ δ = 0.8km ~4s Increasing depth
- 14. Magnetotellurics (MT) 100 ohm.m 10 km 10 ohm.m 1000 ohm.m E(ω ) = Z(ω )B(ω ) ρa = 1 μ 0ω Z Ex RhoXY ≈ Hy 2 NASA φ = arg(Z ) Ey RhoYX ≈ Hx
- 15. Interpretation of the MT Data: • Data ⎛ 0 ⎜ ⎜− Z ⎝ Z⎞ ⎟ 0⎟ ⎠ ⎛ 0 ⎜ ⎜Z ⎝ yx Z xy ⎞ ⎟ 0 ⎟ ⎠ ρ • Inversion • Resistivity Model 2‐D Z xy ⎞ ⎟ Z yy ⎟ ⎠ ρxy, ρyx 1‐D ⎛ Z xx ⎜ ⎜Z ⎝ yx 3‐D
- 17. What is geothermal? 2 • Heat energy of the earth is called geothermal energy. • Geothermal energy exposed to the surface as a result of Earth’s cooling mechanism, convection. 3 1 First geothermal power plant in Larderello in 1904 by Prince Piero Ginori Conti. • 90 countries have geothermal potential and 70 of those already utilized geothermal energy. • USA, Philipines, Iceland, Indonesia and Italy are some of the largest geothermal user countries.
- 19. Regional Tectonics • Northward motion of African and Arabian plates • Closure of the Tehys Ocean 13 Ma • Arabia‐Eurasia collision and uplifting Courtesy of Promete Jeotermal • Development of NAF and EAF • Extrusion of Anatolian Block • Trench roll back and extension.
- 22. Why MT for Geothermal? High resistivity contrast Deep penetration Portable Non‐invasive “Lower” cost after Cumming et al. 2009 after Cumming et al. 2009 Kuyumcu et al., 2009
- 23. Denizli MT Survey • 92 MT sites were collected in April, 2012. Survey area is highly industrialized mainly within the graben. • Remote site was located 60 km away from the grid. • 48kHz, 12kHz and 1kHz (continuous) sampling rates were used for data acquisition. Courtesy of Promete Jeotermal
- 24. Denizli MT Data • High quality 5‐channel MT data were acquired by using Spartan MT data loggers. Courtesy of Promete Jeotermal
- 25. Denizli MT Data • High quality 5‐channel MT data were acquired by using Spartan MT data loggers. Courtesy of Promete Jeotermal
- 26. Denizli MT Data • High quality 5‐channel MT data were acquired by using Spartan MT data loggers. Courtesy of Promete Jeotermal
- 27. Denizli MT Data • High quality 5‐channel MT data were acquired by using Spartan MT data loggers. Courtesy of Promete Jeotermal
- 29. Denizli 3D MT Model Expected cross‐section (2 km) of the Denizli Graben (Akman, 2012) Denizli graben contains two types of infills. 1. Ancient: 660 m thick Middle Miocene‐Middle Pliocene deposits controlled and deformed by ~N‐S extension then compression in the latest Pliocene (Kocyigit, 2005). 2. Modern: 350 m thick, undeformed Plio‐Quaternary deposits (Kocyigit, 2005).
- 30. Denizli 3D MT Model High Res. Low Res. Courtesy of Promete Jeotermal Courtesy of Promete Jeotermal
- 31. Resistivity Cross‐sections South Jeotermal Courtesy of Promete North Courtesy of Promete Jeotermal
- 32. Resistivity Cross‐sections South North Courtesy of Promete Jeotermal Courtesy of Promete Jeotermal
- 35. Conclusions: – Closely spaced MT sites required to build better constrained models as well as static shift control. – Good quality MT data can be collected even around industrialized and populated areas. – MT imaged the sedimentary fill of the Denizli graben and underlying Menderes metamorphics. – Well locations were determined by use of MT, seismic and structural geology to reduce drilling risk. – Computational requirements for 3D inversion has been matched by recent developments on computer clusters. However, most MT surveys are designed as a grid and more MT stations are collected than ever before.