Description
Acoustic waveforms are acquired while drilling with the Schlumberger Drilling and Measurement sonicVISION tool (LWD-SWD6). One transmitter and four receivers are positioned
within a drill collar just above the bit to collect compressional
transit times just seconds after the rock has been cut. As with
all Logging-While-Drilling tools, formation data are collected
before the borehole alteration or invasion occurs. The data are
stored in memory and dumped upon collar retrieval, or they are
pulsed in real time if an MWD tool is in
use. Sonic data are then utilized in the traditional manner for
sonic velocity, synthetic seismogram and correlation with wireline
logs.
Applications
Porosity and "pseudodensity"
log
The sonic transit time can be used to compute porosity by using
the appropriate transform and to estimate fracture porosity
in carbonate rocks. In addition, it can be used to compute a "pseudodensity"
log over sections where this log has not been recorded or the
response was not satisfactory.
Seismic impedance
The product of compressional velocity and density is useful in
computing synthetic seismograms for time-depth ties of seismic
reflectors.
Sonic waveform
analysis
If a refracted shear arrival is present, its velocity can be
computed from the full waveforms, and the frequency content
and energy of both compressional and shear arrivals can also
be determined.
Fracture porosity
Variations in energy and frequency content are indicative of
changes in fracture density, porosity, and in the material
filling the pores. In some cases compressional-wave attenuation
can also be computed from the full waveforms.
Log Presentation
Tool Specifications
| Tool make-up length: |
26 ft (7.9 m) |
| Tool weight: |
2,600 lbs (1,180.4 kg) |
| API nominal collar outside diameter: |
6.75 in (17 cm) |
| Maximum outside diameter: |
7.5 to 9.875 in (19 to 25 cm) |
| Minimum bit size: |
8.5 in (21.6 cm) |
| Maximum bit size: |
14 in (35.6 cm) |
| Maximum Temperature: |
300° F (149° C) |
| Maximum pressure: |
25 kpsi (17.3 kPa) |
| Flow range: |
0-800 gpm |
| Pressure drop coeffecient (C)*: |
256,000 |
| Maximum curvature - sliding: |
16 deg/100 ft (16 deg/31 m) |
| Maximum rotary torque: |
16,000 ft-lbf (4.877 m-lbf) |
| Minimum operating RPM: |
0 rpm |
| Uphole connection: |
5-1/2 FH box |
| Downhole connection: |
5-1/2 FH box |
| (*) pressure drop = [mudweight in ppg] x [flow in gpm]²/C |
Measurement Specifications
| Measurement range: |
40 to Δtmud -20 microsec/ft |
| Accuracy: |
±2 microsec/ft |
| Vertical resolution: |
24 in (61 cm) |
Major Outputs
| CHRA: |
Coherence at compression peak, from receiver array |
| CHTA: |
Coherence at compression peak, from transmitter array |
| DTBC: |
Compressional slowness, borehole compensated (μsec/ft) |
| DTRA |
Compressional slowness, from receiver array (μsec/ft) |
| DTTA: |
Compressional slowness, from transmitter array (μsec/ft) |
| DTCO: |
Compressional slowness, computed downhole (μsec/ft) |
| CHCO: |
Coherence at compression peak, computed downhole |
| ISTB: |
Sonic Time after bit (s) |
Deployment Notes
The LWD-SWD6 is combinable with all other Logging-While-Drilling
tools with no reduction in the drilling rate.
* ®trademark of Schlumberger
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