Well Log Interpretation Sonic Log

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Well Log InterpretationSonic Log
Earth Environmental Science University of
Texas at Arlington
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Sonic Log
The sonic log measures the time, Dt in
microseconds, it takes a compressional wave to
travel through 1 of rock. The units are msec/ft,
the inverse of velocity. The sonic velocity can
be related to seismic velocity.
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Sonic Log
The sonic transit time depends on the lithology,
porosity and fluids in the pore spaces. It also
assumes a homogeneous distribution of porosity.
Vuggy and fracture porosity give spurious results.
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Sonic Log

• To compute porosity from a sonic log, the
  following information is needed
• Dtma transit time through the matrix alone
• Dtfl transit time through the fluid alone
• Dtlog the measured transit time from the log.

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Sonic Log
There are two equations commonly used to compute
sonic velocity Wyllie time averaged
Raymer-Hunt-Gardner (RHG)
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Sonic Log
Cp, a compaction factor, 1 for consolidated
sediments. For unconsolidated sediments
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Sonic Log
If hydrocarbons are present, fs must be reduced
by a factor of 0.7 (gas) or 0.9 (oil)
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Sonic Log Assignment
Using the sonic log on the left, make a
spreadsheet that computes fs for lms, dol and ss
at depths of 9300 and 9369 using both the
Wyllie and RHG equations. Label each parameter.