Comparison of P- and S-wave velocities and Q's from VSP and sonic log data

Journal Article · Sat Oct 01 00:00:00 EDT 1994 · Geophysics; (United States)

DOI:https://doi.org/10.1190/1.1443541· OSTI ID:6645292

De, G S; Winterstein, D F; Meadows, M A ^[1]

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1. Chevron Petroleum Technology Co., La Habra, CA (United States)

The authors compared P- and S-wave velocities and quality factors (Q's) from vertical seismic profiling (VSP) and sonic log measurements in five wells, three from the southwest San Joaquin Basin of California, one from near Laredo, Texas, and one from northern Alberta. Their purpose was to investigate the bias between sonic log and VSP velocities and to examine to what degree this bias might be a consequence of dispersion. VSPs and sonic logs were recorded in the same well in every case. Subsurface formations were predominantly clastic. The bias found was that VSP transit times were greater than sonic log times, consistent with normal dispersion. For the San Joaquin wells, differences in S-wave transit times averaged 1--2 percent, while differences in P-wave transit times averaged 6--7 percent. For the Alberta well, the situation was reversed, with differences in S-wave transit times being about 6 percent, while those for P-waves were 2.5 percent. For the Texas well, the differences averaged about 4 percent for both P- and S-waves. The authors calculated (Q's) from a velocity dispersion formula and from spectral ratios. When the two Q's agreed, they concluded that velocity dispersion resulted solely from absorption. These Q estimation methods were reliable only for Q values smaller than 20. They found that, even with data of generally outstanding quality, Q values determined by standard methods can have large uncertainties, and negative Q's may be common.

• OSTI ID: 6645292
• Journal Information: Geophysics; (United States), Vol. 59:10; ISSN 0016-8033
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
02 PETROLEUM
03 NATURAL GAS
ALBERTA
GEOLOGIC DEPOSITS
CALIFORNIA
SEISMIC SURVEYS
CORRECTIONS
DATA ANALYSIS
TEXAS
SEISMIC WAVES
SONIC LOGGING
CANADA
DEVELOPED COUNTRIES
GEOPHYSICAL SURVEYS
NORTH AMERICA
SURVEYS
USA
WELL LOGGING
580000* - Geosciences
020200 - Petroleum- Reserves
Geology
& Exploration
030200 - Natural Gas- Reserves
Geology
& Exploration