Geophysical Surveys

1
Geophysical Surveys

• Chapter 2 (Part 2)

2
Geophysical Surveys

• Geophysics the study of the physics of the
  earth, its oceans, and its atmosphere.
• What are petroleum geologists looking at?
• Earths magnetism
• Gravity
• Seismic vibrations / Vibrations of the earth

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Geophysical Surveys

• Types
• Magnetic and Electromagnetic Surveys
• Gravity Surveys
• Seismic Surveys

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Magnetic and Electromagnetic

• Basement rock typically has magnetic properties
• Typically Two Types of Surveys
• Magnetometer Surveys
• Magnetollurics

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Magnetometer Survey
- Magnetometer is towed behind an airplane or
ship. - Transmits data to an onboard computer
that records the data. - Micromagnetic
Technique is used to determine micromagnetic
anomalies or deviations
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Magnetotellurics

• The theory that rocks of differing composition
  have different electrical properties.
• Geologist record and measure flow of electricity
  between rocks or across salt water.
• Analyze and interpret the data to reveal
  subsurface structures.

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Gravity Surveys

• Scientist look for slight variations in the
  earths gravitational field caused by the varying
  weight of rocks.
• Very Dense rocks (Weigh more) near the surface
  exert a higher gravitational force than those of
  lower density.
• Salt domes are associated with minimum gravity
• Ordinary Domes and Anticlines are associated with
  maximum gravity
• Tools of the trade
• Torsion Balance
• Gravimeter or Gravity Meter

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Seismic Surveys (Seismology)

• Surveys taken by small artificial seismic
  events bounce energy through the earths
  surface.
• Different layers in the earth bounce
  differently such as sand vs. rock.
• Sensors Geophones pick up the reflected seismic
  waves and send them to a recorder.
• Recorder Seismograph amplifies and records
  their characteristics called a seismogram
• Seismogram generates a two dimensional slice of
  the earth from the surface downward called a
  seismic section.

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Seismic Surveys (Seismology)
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3D Seismic Surveys

• http//www.youtube.com/watch?vf1GeNljM0T8feature
  related

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Early Methods

• Dr. L. Mintrop
• German Scientist who developed one of the first
  practical uses of seismic data.
• He invented a portable seismograph.
• Used it during World War 1
• Determined the position of the allies artillery
  by setting up three seismographs opposite the
  enemy.
• Later came to the Texas Gulf Coast and started
  the Gulf Production Company specializing in
  seismic exploration

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Explosive Methods

• http//www.youtube.com/watch?vjc38hj9JQ_4

13
Thumper Trucks (Vibroseis)
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Marine Seismic Methods

• Typically same methods as on land, but it uses
  hydrophones (marine version of the geophone)

15
Questions

• Define Geophysics.
• List and describe the three types of surveys.
• What are the two types of Magnetic Surveying?
• Is basement rock typically magnetic (yes/No)?
• What is a gravity survey?
• Define seismology.
• List three different methods of seismic
  surveying.
• How do Thumper Trucks create seismic activity
  in the earths surface?
• What is a geophone called in offshore
  applications?
• How do ships create the seismic wave in
  offshore seismic surveying?