Borehole Seismic Techniques
Exploration Technique: Borehole Seismic Techniques
|Exploration Technique Information|
|Exploration Group:||Downhole Techniques|
|Exploration Sub Group:||Borehole Seismic Techniques|
|Parent Exploration Technique:||Downhole Techniques|
|Information Provided by Technique|
|Lithology:||Rock unit density influences elastic wave velocities|
|Stratigraphic/Structural:||Structural geology- faults, folds, grabens, horst blocks, sedimentary layering, discontinuities, etc|
|Hydrological:||Combining compressional and shear wave results can indicate the presence of fluid saturation in the formation|
|Thermal:||High temperatures and pressure impact the compressional and shear wave velocities|
Borehole Seismic Techniques are any seismic technique where either the source or receivers are lowered down a borehole. Downhole seismic surveys can be carried out in boreholes that are open or cased, and usually take place once drilling operations are completed. The main benefits of borehole seismology compared to surface seismology are higher resolution, enhanced velocity model around a well, no depth uncertainties, and less near-surface distortions.
For successful borehole seismic surveys it is important to establish the orientation of down hole geophones because they can rotate as they travel down the borehole. Once they are in position the orientation can be determined by an offset surface orientation shot. It is also very important that the geophones have a good coupling with the borehole wall.
Borehole seismic techniques can be more expensive compared to surface seismic techniques because more robust equipment is needed to handle the higher pressures, temperatures and fluids encountered downhole.
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