SRS - Seismic Reference Survey
The seismic reference tool carries a sensitive geophone to detect an acoustic pulse travelling from a seismic source at ground level. A powerful motor-driven caliper arm ensures that the sonde is locked securely against the borehole wall while the measurement is taking place.The seismic source is normally a high pressure airgun placed in a fluid filled pit for efficient acoustic coupling. This can be replaced by conventional explosive seismic sources or by the client's own wave propagating device.
Wireline logs of Gamma, Density, Sonic Velocity, Acoustic Impedance and Caliper
The time taken for the energy to travel from surface to geophone is recorded for each depth station in the borehole. These times are used to calibrate integrated times from P-wave sonic logs as part of the Synthetic Seismogram generation process.
As well as the SRS Check-shot, Wireline Alliance offers a VSP logging service based on the Avalon data capture system. This can employ either an airgun or a Vibroseis truck arranged by the client.
The data capture process is similar to the SRS operation but stations are usually only 5 metres apart.The sonde offers 3D propagation measurement.
VSP Vertical Seismic Profile
The VSP log requires multiple shots to be stacked at each station so, at 5 metre station separation, hundreds of shots are fired.
If an airgun is used, the water pit needs to be much bigger and better supported than the one employed in the SRS operation.
A suspended airgun is fired in a 2 metre deep lined pit.