Low-frequency P-wave logging for improved compressional velocity in slow formation gas zones

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:542814

Wu, P T; Darling, H L; Scheibner, D

The ratio of compressional to shear velocity is commonly used as a gas indicator, for seismic correlation, and for rock mechanical properties evaluation in the oil industry. However, in soft rock gas zone, it is difficult to obtain a good measure of compressional velocity. Traditional monopole sonic logging tools operate with source frequencies above 10 kHz, giving rise to large amplitude borehole fluid modes which dominate compressional wave traveling with speed slower than the fluid speed. Numerical modeling of monopole sonic waveforms in a fluid-filled borehole in porous formations confirms these observations, but also shows that at significantly lower frequencies two important changes occur: (1) the non-Stoneley fluid modes becomes extremely small, and (2) the P-wave amplitude is greatly increased. Therefore, at low frequencies, logging of these very slow P-waves in gas zones should be feasible. A field example shows the value of this low frequency technique, resulting in measurements of P-wave velocities substantially lower than the fluid speed.

• OSTI ID: 542814
• Report Number(s): CONF-951013--
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
58 GEOSCIENCES
ACOUSTIC MEASUREMENTS
EXPLORATION
NATURAL GAS DEPOSITS
NATURAL GAS WELLS
RESERVOIR ROCK
SEISMIC S WAVES
SHEAR PROPERTIES
SONIC LOGGING