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Geophysics Lab: Reflection Raypath and NMO Equation, Exercises of Geology

Dr. B.R. Ambedkar Open UniversityGeology

Instructions for drawing reflection raypaths on a geophysics lab diagram, deriving the non-approximated reflection time equation using pythagora's theorem, and discussing the differences between two-way traveltime and nmo terms. It also covers the approximated nmo equation, calculating layer velocities from reflection hyperbolas, and the reasons why a seismic section is not a true image of the subsurface.

Typology: Exercises

2012/2013

Uploaded on 04/29/2013

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arpanay ๐Ÿ‡ฎ๐Ÿ‡ณ

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Normal๎˜ƒMove๎˜ƒOut:๎˜ƒ๎˜ƒGeophysics๎˜ƒLab๎˜ƒ๎˜ƒ
Draw๎˜ƒa๎˜ƒreflection๎˜ƒraypath๎˜ƒon๎˜ƒthe๎˜ƒfollowing๎˜ƒdiagram๎˜ƒand๎˜ƒlabel๎˜ƒthe๎˜ƒvertices๎˜ƒand๎˜ƒangles๎˜ƒof๎˜ƒthe๎˜ƒtwo๎˜ƒright๎˜ƒ
triangles๎˜ƒformed๎˜ƒby๎˜ƒthe๎˜ƒraypath.๎˜ƒDerive๎˜ƒthe๎˜ƒnonโ€approximated๎˜ƒreflection๎˜ƒtime๎˜ƒequation๎˜ƒusing๎˜ƒ
Pythagoraโ€™s๎˜ƒtheorem๎˜ƒ(Eqn.๎˜ƒ7.1).๎˜ƒAssume๎˜ƒan๎˜ƒupper๎˜ƒlayer๎˜ƒvelocity๎˜ƒand๎˜ƒthickness๎˜ƒof๎˜ƒv1๎˜ƒand๎˜ƒh1.๎˜ƒ
๎˜ƒ
๎˜ƒ
S
R
1. Multiple๎˜ƒout๎˜ƒyour๎˜ƒNMO๎˜ƒequation๎˜ƒto๎˜ƒget๎˜ƒtwo๎˜ƒterms๎˜ƒ(Eqn.๎˜ƒ7.1)๎˜ƒand๎˜ƒidentify๎˜ƒthe๎˜ƒtwoโ€way๎˜ƒtravelโ€
time๎˜ƒ(t0)๎˜ƒand๎˜ƒNMO๎˜ƒterms.๎˜ƒDefine๎˜ƒin๎˜ƒwords๎˜ƒthe๎˜ƒdifference๎˜ƒbetween๎˜ƒthese๎˜ƒtwo๎˜ƒterms๎˜ƒ(Eqn.๎˜ƒ7.2).๎˜ƒ
๎˜ƒ
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2. Use๎˜ƒthe๎˜ƒapproximated๎˜ƒNMO๎˜ƒequation๎˜ƒ(Eqn.๎˜ƒ7.3),๎˜ƒsolve๎˜ƒfor๎˜ƒthe๎˜ƒvelocity๎˜ƒof๎˜ƒlayer๎˜ƒone๎˜ƒ(v1)๎˜ƒfunction๎˜ƒ
(Eqn.๎˜ƒ7.4).๎˜ƒWhat๎˜ƒvariables๎˜ƒare๎˜ƒmeasured๎˜ƒfrom๎˜ƒthe๎˜ƒseismic๎˜ƒrecord๎˜ƒto๎˜ƒcalculate๎˜ƒthe๎˜ƒvelocity.๎˜ƒ
๎˜ƒ
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3. Derive๎˜ƒthe๎˜ƒequation๎˜ƒused๎˜ƒto๎˜ƒcalculate๎˜ƒthe๎˜ƒtwoโ€way๎˜ƒreflection๎˜ƒtravelโ€time๎˜ƒ(t0).๎˜ƒ
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4. The๎˜ƒbook๎˜ƒ(pg.๎˜ƒ84)๎˜ƒdefines๎˜ƒreasons๎˜ƒwhy๎˜ƒa๎˜ƒseismic๎˜ƒsection๎˜ƒis๎˜ƒNOT๎˜ƒa๎˜ƒtrue๎˜ƒimage๎˜ƒof๎˜ƒthe๎˜ƒsubsurface.๎˜ƒ
What๎˜ƒare๎˜ƒthey?๎˜ƒ
๎˜ƒ
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Download Geophysics Lab: Reflection Raypath and NMO Equation and more Exercises Geology in PDF only on Docsity!

Normal Move Out: Geophysics Lab Draw a reflection raypath on the following diagram and label the vertices and angles of the two right triangles formed by the raypath. Derive the nonโ€approximated reflection time equation using Pythagoraโ€™s theorem (Eqn. 7.1). Assume an upper layer velocity and thickness of v 1 and h 1. S R

  1. Multiple out your NMO equation to get two terms (Eqn. 7.1) and identify the twoโ€way travelโ€ time (t 0 ) and NMO terms. Define in words the difference between these two terms (Eqn. 7.2).
  2. Use the approximated NMO equation (Eqn. 7.3), solve for the velocity of layer one (v 1 ) function (Eqn. 7.4). What variables are measured from the seismic record to calculate the velocity.
  3. Derive the equation used to calculate the twoโ€way reflection travelโ€time (t 0 ).
  4. The book (pg. 84) defines reasons why a seismic section is NOT a true image of the subsurface. What are they?

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  1. The following graph shows three reflection hyperbolas for three different layer velocities. Using the velocity equation (Eqn. 7.4), calculate the layer velocities for the three reflection hyperbolas. Top hyperbola velocity ______ Middle Hyp. velocity _______ Bottom Hyp. velocity _________
  2. If multiple layers are analyzed, write down the equation that defines the velocity definition to be used in equation 7.2 and define the terms in words.
  3. Write down Dixโ€™s formula (Eqn. 7.7) and define the variables. Define what the layer velocity (Vlayer ) and the rootโ€meanโ€square (RMS) velocity (V (^) rms ) are used to calculate.

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