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Questions and Answers
What is a key advantage of EM methods over contacting electrical resistivity surveys?
What is a key advantage of EM methods over contacting electrical resistivity surveys?
- Greater penetrating depth
- Improved data quality
- Faster survey times (correct)
- No requirement for inductive coupling
What is the main difference between Active and Passive Electromagnetic methods?
What is the main difference between Active and Passive Electromagnetic methods?
- The type of measurement used
- The frequency of the signal
- The source of the electromagnetic field (correct)
- The depth range of investigation
What is one of the main applications of electromagnetic methods in terms of resource assessment and exploration?
What is one of the main applications of electromagnetic methods in terms of resource assessment and exploration?
- Mineral resource assessment and exploration (correct)
- Geothermal resource investigations
- Contaminant plume mapping
- Hydrocarbon reserve monitoring
In which type of land model do EM surveys counter survey difficulties?
In which type of land model do EM surveys counter survey difficulties?
What is the primary factor that affects the level of inquiry in TEM?
What is the primary factor that affects the level of inquiry in TEM?
What is the relationship between the distance between the transmitter and receiver coils and the depth range under investigation in FEM?
What is the relationship between the distance between the transmitter and receiver coils and the depth range under investigation in FEM?
What is the main parameter measured by Electromagnetic and Electric methods?
What is the main parameter measured by Electromagnetic and Electric methods?
What is the purpose of Electromagnetic methods?
What is the purpose of Electromagnetic methods?
Which of the following is NOT a typical use of electromagnetic methods?
Which of the following is NOT a typical use of electromagnetic methods?
What are the three types of measurements that can be conducted using Electromagnetic methods?
What are the three types of measurements that can be conducted using Electromagnetic methods?
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Study Notes
Basic Concepts
- Electromagnetic methods are categorized into two types: Active (controlled source) methods and Passive (natural field) methods.
- Controlled source methods include GBR and MagnetoMetric resistivity, while natural field methods include Magnetotelluric and Telluric Methods.
- Electromagnetic methods can be classified as frequency-domain (FEM) or time-domain (TEM) systems.
- These methods measure the electrical conductivity (resistivity) of the Earth's materials, which is the same measured parameter as Electric methods, but with different measurement methods.
- Electromagnetic methods can be used for land-based and airborne surveys, marine surveys, and borehole logging.
- Surveys can be conducted through three types of measurements: mapping, profiling, and sounding.
- Electromagnetic methods provide information about the variation in conductivity within a certain depth range.
TEM Method
- The level of inquiry is closely correlated with the loop size, recording time interval, and shut-off time in TEM.
- TEM methods have a greater penetrating depth than electric methods.
Advantages
- One of the main advantages of EM methods is that they do not require direct contact with the ground.
- EM surveys can be made faster than equivalent surveys using contacting electrical resistivity.
- EM methods counter some survey difficulties with land models having very conductive uppermost layers.
Uses
- Electromagnetic methods are applicable for:
- Mineral resource assessment and exploration
- Investigating and monitoring hydrocarbon reserves
- Surveys of groundwater
- Mapping contaminant plumes
- Geothermal resource investigations
- Contaminated land mapping
- Landfill surveys
- Finding man-made and natural cavities
- Location of geological faults
- Geological mapping and Permafrost mapping
- UneXploded Ordnance (UXO)
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