Vertical seismic profile
In geophysics, Vertical Seismic Profile (VSP) is a technique of seismic measurements used for correlation with surface seismic data. The defining characteristic of a VSP (of which there are many types) is that either the energy source, or the detectors (or sometimes both) are in a borehole. In the most common type of VSP, Hydrophones, or more often geophones or accelerometers, in the borehole record reflected seismic energy originating from a seismic source at the surface.
A class of borehole seismic measurements used for correlation with surface seismic data, for obtaining images of higher resolution than surface seismic images and for looking ahead of the drill bit; also called a VSP. Purely defined, VSP refers to measurements made in a vertical wellbore using geophones inside the wellbore and a source at the surface near the well. In the more general context, VSPs vary in the well configuration, the number and location of sources and geophones, and how they are deployed. Most VSPs use a surface seismic source, which is commonly a vibrator on land and an air gun in offshore or marine environments. VSPs include the zero-offset VSP, offset VSP, walkaway VSP, walk-above VSP, salt-proximity VSP, shear-wave VSP, and drill-noise or seismic-while-drilling VSP. A VSP is a much more detailed survey than a check-shot survey because the geophones are more closely spaced, typically on the order of 25 m [82 ft], whereas a check-shot survey might include measurements of intervals hundreds of meters apart. Also, a VSP uses the reflected energy contained in the recorded trace at each receiver position as well as the first direct path from source to receiver. The check-shot survey uses only the direct path traveltime. In addition to tying well data to seismic data, the vertical seismic profile also enables converting seismic data to zero-phase data and distinguishing primary reflections from multiples.
There are numerous methods for acquiring a vertical seismic profile (VSP). Zero-offset VSPs (A) have sources close to the wellbore directly above receivers. Offset VSPs (B) have sources some distance from the receivers in the wellbore. Walkaway VSPs (C) feature a source that is moved to progressively farther offset and receivers held in a fixed location. Walk-above VSPs (D) accommodate the recording geometry of a deviated well, having each receiver in a different lateral position and the source directly above the receiver. Salt-proximity VSPs (E) are reflection surveys to help define a salt-sediment interface near a wellbore by using a source on top of a salt dome away from the drilling rig. Drill-noise VSPs (F), also known as seismic-while-drilling (SWD) VSPs, use the noise of the drill bit as the source and receivers laid out along the ground. Multi-offset VSPs (G) involve a source some distance from numerous receivers in the wellbore.
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