Acoustic waveforms are acquired while drilling with the Schlumberger Logging-While-Drilling-sonicVISION tool (LWD-sonicVISION). 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 a MWD tool is in use. Sonic data are then utilized in the traditional manner for sonic velocity, synthetic seismograms and correlation with wireline logs.
Porosity and “pseudodensity”. 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.
|Temperature rating:||300° F (149° C)|
|Pressure rating:||25 kpsi (17.2 MPa)|
|Tool make-up length:||23.8 ft (7.3 m)|
|Tool weight:||2,600 lbs (1,180.4 kg)|
|API nominal collar outside diameter:||6.75 in (17 cm)|
|Maximum outside diameter:||6.9 in (17.5 cm)|
|Minimum bit size:||8.5 in (21.6 cm)|
|Maximum bit size:||14 in (35.6 cm)|
|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|
|Vertical resolution:||24 in (61 cm)|
|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, computed downhole (μsec/ft)|
|DTCO:||Compressional slowness, computed downhole (μsec/ft)|
|CHCO:||Coherence at compression peak, computed downhole|
|ISTB:||Sonic Time after bit (s)|
The LWD-sonicVISION is combinable with all other Logging-While-Drilling tools with no reduction in the drilling rate.
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