Standoff compensation for acoustic logging while drilling systems
US5726951A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Apr 28, 1995 |
| Grant date | Mar 10, 1998 |
| Priority date | — |
| Expiry date | Apr 28, 2015 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V1/44
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A standoff compensation system is disclosed for use in an acoustic LWD system. An acoustic transducer is provided to measure the standoff distance between the logging tool and the borehole wall. The present invention includes a downhole processor for determining an index value which is used to align received acoustic formation signal measurements based upon the measured standoff distance. The index value can either be calculated by the downhole processor or can be retrieved from a pre-calculated look-up table in ROM. The processor then shifts the received acoustic formation signals based upon the index value assigned to each formation signal. The aligned acoustic formation signals are stacked, so that a single acoustic formation signal can be obtained for each firing period and either stored in downhole memory, used immediately, or transmitted by telemetry to the surface. The firing of the acoustic formation transmitters occurs in a rapid firing mode, followed by a relatively long idle. The rapid firing mode further minimizes the amount of data which must be stored, while providing an idle period for aligning and stacking the received signals.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.