Wave Reflection and Refraction
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Questions and Answers

What can occur when the seismic data have not been correctly interpreted?

  • The interpretor is guaranteed to pick the correct reflector
  • Seismic lines are shot on a non-intersecting grid
  • Reflectors can be mapped accurately
  • The 'bow tie' effect is produced (correct)

    • What is the primary purpose of mapping reflectors?

  • To identify the location of seismic lines
  • To create contour maps of the reflecting horizons (correct)
  • To determine the type of rock present at the reflector
  • To calculate the depth of the reflecting horizon

    • What is the term used to describe when the interpreter incorrectly jumps a reflecting horizon?

  • Leg (correct)
  • Syncline
  • Isochron
  • Bow tie

    • What type of maps are constructed from the reflectors picked on seismic lines?

    <p>Time maps</p> Signup and view all the answers

    What is the purpose of tracing reflectors from line to line in a loop?

    <p>To check that the reflector has been correctly picked</p> Signup and view all the answers

    What is the role of seismic surveying in petroleum exploration and production?

    <p>It is an essential part of the whole cycle</p> Signup and view all the answers

    What happens to some of the energy when a wave reaches a boundary between two media with different acoustic impedance?

    <p>Some of the energy is reflected back into the upper medium</p> Signup and view all the answers

    What is the relationship between velocity and density in a homogenous lithology?

    <p>Velocity and density generally increase with depth</p> Signup and view all the answers

    What is the range of possible values for a reflection coefficient?

    <p>-1 to +1</p> Signup and view all the answers

    What is the characteristic of a strong reflector in terms of its reflection coefficient?

    <p>A reflection coefficient of +0.2 or -0.2</p> Signup and view all the answers

    What is the reason for the occurrence of negative reflection coefficients?

    <p>A decrease in acoustic impedance across the reflecting interface</p> Signup and view all the answers

    What is the general tendency of the reflection coefficients at the boundary between two units?

    <p>They tend to appear with approximately equal frequency</p> Signup and view all the answers

    What is the primary purpose of 4D seismic surveys?

    <p>To monitor the movement of fluids during the life of a field</p> Signup and view all the answers

    What is seismic attribute analysis used for?

    <p>To make interpretations about reservoir characteristics</p> Signup and view all the answers

    What is the main application of seismic surveys in the petroleum industry?

    <p>To detect subsurface structures and reservoirs</p> Signup and view all the answers

    What is the term for the analysis of seismic data to identify patterns and trends?

    <p>Seismic attribute analysis</p> Signup and view all the answers

    What is the term for the use of seismic data to create a 3D model of the subsurface?

    <p>Seismic modeling</p> Signup and view all the answers

    How many geophysical methods are mentioned in the text?

    <p>8</p> Signup and view all the answers

    What is the characteristic of oil in terms of uranium and thorium content?

    <p>High uranium but low thorium content</p> Signup and view all the answers

    What type of radiation is normally detected in geophysical work?

    <p>ɤ radiation</p> Signup and view all the answers

    Why are 'metalled' roads not suitable for radioactive surveys?

    <p>Because the radioactivity of the materials in the roads vitiates the observations</p> Signup and view all the answers

    What is the main factor contributing to the background radiation?

    <p>Cosmic rays, potassium-40, and uranium and thorium in rocks</p> Signup and view all the answers

    What is the minimum threshold for a reading to be considered significant?

    <p>3-4 times the background</p> Signup and view all the answers

    How are radioactive surveys typically conducted?

    <p>By walking along pre-laid lines holding the detector some 40-50 cm above the ground</p> Signup and view all the answers

    What is the primary reason behind the development of geophysical methods employing radioactivity?

    <p>To meet the demand for uranium metal in atomic reactors</p> Signup and view all the answers

    What happens to the energy of α and ß particles when they pass through matter?

    <p>It decreases exponentially with distance</p> Signup and view all the answers

    What is the approximate range of α particles in air at 18° C?

    <p>A few centimeters</p> Signup and view all the answers

    What can be used to completely stop β particles?

    <p>A thin sheet of lead</p> Signup and view all the answers

    What is the relationship between the intensity of γ rays and distance?

    <p>The intensity decreases exponentially with distance</p> Signup and view all the answers

    What is the scope of geophysical methods employing radioactivity?

    <p>Beyond just searching for ores of radioactive metals or minerals associated with them</p> Signup and view all the answers

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