John W. Minear

Acoustic attenuator, well logging apparatus and method of well logging

Disclosed is a sonic well tool for performing acoustic investigations of subsurface geological formations penetrated by a borehole. The well tool generally includes a longitudinally extending body for positioning in said borehole. The tool also includes a transmitter supported by the body for transmitting acoustic energy, and a receiver supported by the body for receiving acoustic energy. Finally, the tool includes an acoustic attenuation section positioned on the body between the transmitter and the receiver. This section includes one or more cavities defined by the body, inertial mass members positioned inside the cavities in a suitable manner to form a gap between the wall of the cavity and the inertial mass members, and an acoustical attenuation fluid in the gap. The method for attenuating sonic waves generally includes transmitting a sonic wave from the transmitter to the tool, passing the sonic wave through the acoustic attenuation section, and receiving attenuated wave at the receivers.

Clay Models and Acoustic Velocities

Acoustic velocity, or porosity derived from the velocity, is often corrected for shale or clay effects. These corrections are largely empirical. Two-phase porous media models are applicable to sedimentary formations and provide a new approach to estimating the effects of shale and clay on clean formations. One particular model is used to calculate the effects of laminated and structural shale and dispersed clay on compressional and shear wave slowness. The calculations suggest that laminated and structural shale have about the same effect. Dispersed clay may have negligible effect. Shale and clay increase shear wave slowness more than compressional wave slowness.

Full Wave Acoustic Logging: Some Examples

Abstract More information about formation properties than is commonly utilized is available in the acoustic signal. The objective of full-wave acoustic logging is to use more of this information to determine formation properties. Full-wave acoustic tools generally have transmitter-to-receiver spacings greater than about eight feet. This provides deeper penetration and facilitates signal analysis. Full-wave acoustic signals are briefly discussed. Shear wave slowness, or Δts, is one of the most important new acoustic logging measurements. Used with Δtp, Δts provides basic log quantities for lithology identification, gas zone identification, estimation of lithology and porosity with acoustic logs only, and improved formation elastic property estimation.