What is a Checkshot?
PetroWiki. In a seismic context, a check shot survery determines formation seismic wave velocities over specific intervals. Measurement is made of travel time from surface to downhole geophones.
What is the difference between Checkshot and VSP?
The basic difference between the check shot survey and the VSP is that the VSP measures nearly all seismic waveforms in the well bore (up-going and down-going energy), whereas the check shot velocity survey measures basically only the down-going energy (Figure 1).
What is well Checkshot?
checkshot survey 1. n. [Geophysics] A type of borehole seismic data designed to measure the seismic traveltime from the surface to a known depth.
What is VSP method?
In geophysics, vertical seismic profile (VSP) is a technique of seismic measurements used for correlation with surface seismic data. 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.
What is the purpose of synthetic seismogram?
In earthquake seismology, synthetic seismograms are used either to match the predicted effects of a particular earthquake source fault model with observed seismometer records or to help constrain the Earth’s velocity structure. Synthetic seismograms are generated using specialized geophysical software.
What is VSP in oil and gas?
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. 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.
What is seismic well tie?
A seismic-to-well tie is the process through which seismic data wavelets are understood and compares seismic data at a well location with log data from the well.
Why is seismic profiling vertical?
Vertical seismic profiling has been a useful measurement to obtain rock properties (velocity, impedance, attenuation, anisotropy) in depth as well as to provide a seismic image of the subsurface.
How is synthetic seismic data generated?
Required steps to generate seismogram:
- Data Preparation (Unit conversion and Sonic / Density Logs processing)
- Time-Depth relationship construction.
- Acoustic Impedance(AI or Z) Calculation.
- Reflection Coefficient(Rc) calculation.
- Resampling to the time domain and Rc recalculation.
- Wavelet & Convolution.
What is the purpose of a checkshot survey?
Borehole surveys can be divided into checkshots surveys and vertical seismic profiles, or VSP s. Checkshot surveys are run for the purpose of obtaining the time picks from the direct arrivals from the source, shown as the orange lines in figure 2.
What should be the source of a checkshot?
The source—receiver geometry used in onshore velocity checkshots is shown in Figure 1. If possible, the energy source should be the same as that used to record the surface seismic data near the well.
Where can I find the velocity of a checkshot?
Checkshot time, depth and velocity information can be extracted from VSP surveys. Figure 3 depicts a zero offset source being used to acquire a checkshot in a straight well. The source is usually not right at the well for noise considerations and to avoid damage to the rig, but placed approximately 30 meters from the wellhead.
How is the time datum chosen for a checkshot?
Onshore, an arbitrary depth coordinate is chosen as the time datum. In Figure 1, the datum is above the shot depth, and in such a case, the vertical distance between the shot depth and the datum depth is divided by the velocity in that interval. That time adjustment is then added to the measured traveltime to each receiver.