Acoustic Logs

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Exploration Technique: Acoustic Logs

Exploration Technique Information
Exploration Group: Downhole Techniques
Exploration Sub Group: Well Log Techniques
Parent Exploration Technique: Well Log Techniques
Information Provided by Technique
Lithology: determine porosity of layers
Stratigraphic/Structural: map discontinuities to determine their orientation.
Cost Information
Low-End Estimate (USD): 1.00100 centUSD
1.0e-3 kUSD
1.0e-6 MUSD
1.0e-9 TUSD
/ foot
Median Estimate (USD): 4.62462 centUSD
0.00462 kUSD
4.62e-6 MUSD
4.62e-9 TUSD
/ foot
High-End Estimate (USD): 16.001,600 centUSD
0.016 kUSD
1.6e-5 MUSD
1.6e-8 TUSD
/ foot
Time Required
Low-End Estimate: 8.39 days0.023 years
201.36 hours
1.199 weeks
0.276 months
/ job
Median Estimate: 16.08 days0.044 years
385.92 hours
2.297 weeks
0.528 months
/ job
High-End Estimate: 32.17 days0.0881 years
772.08 hours
4.596 weeks
1.057 months
/ job
Additional Info
Cost/Time Dependency: Depth, Temp, Resolution
Acoustic Logs:
A display of traveltime of acoustic waves versus depth in a well. The term is commonly used as a synonym for a sonic log. Some acoustic logs display velocity.
Other definitions:Wikipedia Reegle

The acoustic log exploration technique includes those techniques that use a transducer to transmit an acoustic wave through the fluid in the well and surrounding elastic materials. Several different types of acoustic logs are used, based on the frequencies used, the way the signal is recorded, and the purpose of the log. All these logs require fluid in the well to couple the signal to the surrounding rocks. There are four main types: acoustic velocity, acoustic waveform, cement bond, and acoustic televiewer.
Use in Geothermal Exploration
Acoustic logs are used to determine the lithology and porosity of the rocks surrounding the well. This information can be helpful for determining future well locations and potential areas for well bore stimulation. The log when combined with other logs run provides the basis for a detailed analysis of lithologies, alteration, stratigraphy, etc.

Field Procedures
The geophysical/well logging service company conducts the down hole logging operation and produces both digital and hard copy logs. The Drilling contractor trips the drill pipe and bit and conditions the well bore for logging.

Data Access and Acquisition
Most acoustic-velocity probes employ magnetorestrictive or piezoelectric transducers that convert electrical energy to acoustic energy. Most of the transducers are pulsed from 2 to 10 or more times per second, and the acoustic energy emitted has a frequency in the range of 20 to 35 kHz. Acoustic probes are centralized with bow springs or rubber fingers so the travel path to and from the rock will be of consistent length. Some of the energy moving through the rock is refracted back to the receivers. The receivers reconvert the acoustic energy to an electrical signal, which is transmitted up the cable. At the surface, the entire signal may be recorded digitally for acoustic waveform logging, or the transit time between two receivers may be recorded for velocity logging. Amplitude of portions of the acoustic wave also may be recorded; that technique is described later under waveform logging.
Best Practices
Probes are constructed of low-velocity materials, producing the shortest travel path for the acoustic pulse through the borehole fluid and the adjacent rocks, which have a velocity faster than that of the fluid.
Potential Pitfalls
An unstable well bore (sluffing, wash outs, etc) can be of concern in any well logging operation. In extreme condition, the loss of the logging tool down hole could possibly result in the loss of the hole and would require premature abandonment or the necessity to side track to complete the well drilling operation.

NEPA Analysis
Well logging is a standard operation associated with the drilling permit approval and is included in the downhole analysis of the drilling program.

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