Inverse vertical seismic profiling using a measurement while drilling tool as a seismic source
US5901113A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 12, 1996 |
| Grant date | May 4, 1999 |
| Priority date | — |
| Expiry date | Mar 12, 2016 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V2210/161
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A reverse VSP system is provided and uses a frequency-controllable modulator of an MWD tool as a downhole seismic source. The modulator has a rotor and stator arranged to provide substantially sinusoidal outputs, and is controlled to provide a "Vibroseis"-type frequency sweep (preferably from 1 Hz to 50 Hz). With the bit of the MWD tool in contact with the bottom of the borehole, the force generated by the frequency-controllable modulator will generate measurable axial compressional (P-) waves. These waves which move through the formation are detected by an array of geophones on the formation surface, and a reference signal is obtained by a kelly-mounted accelerometer or strain gauge. The reference signal and signals obtained by the geophones are processed using known signal processing techniques. The disclosed downhole frequency-controllable seismic source provides many advantages including: good resolution due to the ability to output a sinusoidal wave at desired frequencies and the fact that the location of the source signal is well-defined (at the bit), the ability to image formations ahead of the bit, and the ability to conduct reverse VSP processing without adding downhole ha…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.