This highly compact tool is designed specifically for geotechnical and mining applications. The probe measures high (HR) and medium (MR) resolution transit-time and full-waveform data simultaneously from three receivers. The HR measurement gives good resolution of bed boundaries while the MR provides the average formation velocity even in the presence of moderate caving. Shear-wave velocities from full-wave data may be used to calculate rock elasticity parameters.
Principles of Measurement
The piezoelectric transmitter is stimulated by a high-voltage pulse and radiates a high-frequency sonic wave through the borehole fluid and formation to a receiver. An accurate quartz clock measures the first arrival transit time.
Compensated sonic mode:
Three receivers are used. The probe measures the velocity of the first compressional arrival at each receiver. The difference in arrival times between each pair of receivers allows determination of the formation velocity independent of the borehole fluid path.
Full waveform sonic mode:
The probe records the full sonic wave-train at all three receivers simultaneously and also the velocity of the first arrival at each. The data can be displayed as a variable-density log (VDL) or as a waveform (wiggle trace). The waveform data may exported to 3rd-party packages for calculation of compressional, shear and Stoneley velocities.
Features
Short probe can be handled by single operator and easily shipped
Slim diameter for narrow boreholes
Rigid construction for effective centralisation
Down-hole digitisation of waveform data at 1cm interval
Data rate selectable up to 200kbaud for maximum logging speed Detection gain and threshold under operator control.
Detection point and wavelet visible on 'oscilloscope' display during logging
Measurements
Formation velocity (slowness)
Time of first arrival (delta-t)
Integrated transit time
Full waveform from 3 receivers simultaneously
Shear and Stoneley velocities (requires precessing software)
Applications
Geotechnical
Fracture and permeability indication in hard rock \
Mining
Rock strength and elasticity Lithology identification
Water
Correction of seismic velocity Porosity
Operating Conditions
Borehole type
Sonic: open-hole, water-filled
Centralisation: 2 essential
