Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Applying magnetotellurics

  | chapter = Applying magnetotellurics

  | frompg  = 16-1

  | frompg  = 16-4

  | topg    = 16-12

  | topg    = 16-4

  | author  = Arnie Ostrander

  | author  = Arnie Ostrander

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch16/ch16.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch16/ch16.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

Magnetotellurics (MT) is an electrical geophysical technique that measures the resistivity of the subsurface. Although MT cannot provide the resolution of [[Seismic data|seismic surveys]], it is less expensive and, more importantly, can be used in places where seismic data collection is impractical or gives poor results. This is the same physical parameter that is measured in a borehole resis- tivity log.

Magnetotellurics (MT) is an electrical geophysical technique that measures the [[Electrical_methods#Electrical_properties_of_materials|resistivity]] of the subsurface. Although MT cannot provide the resolution of [[Seismic data|seismic surveys]], it is less expensive and, more importantly, can be used in places where seismic data collection is impractical or gives poor results. This is the same physical parameter that is measured in a borehole [[Basic_open_hole_tools#Resistivity|resistivity log]].

==How MT differs from electric logs==

==How magnetotellurics differs from electric logs==

[[Applying-magnetotellurics fig16-1.png|thumb|{{figure number|1}} Simplified relationship between a lithologic log, an electric log, an MT sounding, and an inversion run using the MT sounding data.]]

[[File:Applying-magnetotellurics fig16-1.png|thumbnail|300px|{{figure number|1}}Simplified relationship between a lithologic log, an electric log, an MT sounding, and an inversion run using the MT sounding data.]]

MT differs from an inductive electric log in three major ways:

MT differs from an inductive electric log in three major ways:

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[[:Applying-magnetotellurics fig16-1.png|Figure 1]] shows the simplified relationship between a lithologic log, an electric log, an MT sounding, and an inversion run using the MT sounding data. We can also take electric log data and run a forward MT model to produce an MT sounding curve.

[[:file:Applying-magnetotellurics fig16-1.png|Figure 1]] shows the simplified relationship between a lithologic log, an electric log, an MT sounding, and an inversion run using the MT sounding data. We can also take electric log data and run a forward MT model to produce an MT sounding curve.

==Subsurface layers resolved==

==Subsurface layers resolved==

Subsurface layers are resolved by inverse modeling of MT data acquired across a spec- trum of frequencies, as illustrated in [[:Applying-magnetotellurics fig16-1.png|Figure 1]].

Subsurface layers are resolved by inverse modeling of MT data acquired across a spectrum of frequencies, as illustrated in [[:file:Applying-magnetotellurics fig16-1.png|Figure 1]].

==MT resolution==

==Magnetotellurics resolution==

The rule-of-thumb for MT resolution for depth of burial vs. layer thickness is 10:1. For example, to “see” a layer at a depth of 1,500 m (5,000 ft), the thickness of the layer needs to be approximately 150 m (500 ft) or more. Low-resistivity layers are more easily delineated than high-resistivity layers. It is difficult for MT to resolve more than three or four subsurface layers.

The rule of thumb for MT resolution of depth of burial vs. layer thickness is 10:1. For example, to “see” a layer at a depth of 1,500 m (5,000 ft), the thickness of the layer needs to be approximately 150 m (500 ft) or more. Low-resistivity layers are more easily delineated than high-resistivity layers. It is difficult for MT to resolve more than three or four subsurface layers.

==See also==

==See also==

* [[What is magnetotellurics (MT)?]]

* [[Magnetotellurics survey measurements]]

* [[What does an MT survey measure?]]

* [[Magnetotelluric data acquisition]]

* [[How are MT data acquired?]]

* [[Magnetotellurics case history: frontier basin analysis (Amazon Basin, Colombia)]]

* [[Case history: frontier basin analysis (Amazon Basin, Colombia)]]

* [[Magnetotellurics case history: rugged carbonate terrain (Highlands of Papua New Guinea)]]

* [[Case history: rugged carbonate terrain (Highlands of Papua New Guinea)]]

* [[Magnetotellurics case history: Precambrian overthrust (Northwestern Colorado)]]

* [[Case history: Precambrian overthrust (Northwestern Colorado)]]

* [[Magnetotellurics case history: volcanic terrain (Columbia River Plateau)]]

* [[Case history: volcanic terrain (Columbia River Plateau)]]

==External links==

==External links==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Applying magnetotellurics]]

[[Category:Applying magnetotellurics]]