VSP acquisition with high spatial sampling in the same operational time as a checkshot: 10 minutes
Instead of deploying a conventional borehole seismic tool, Schlumberger proposed using the hDVS distributed acoustic sensing (DAS) system to avoid the 15 hours that would be required for the dedicated logging runs. The system’s optical interrogator unit at surface would be connected to the optical fiber of the hybrid wireline heptacable to collect seismic data along the entire length of the cable used to convey other wireline tools.
No time is required for rigging up and down and conducting a separate seismic tool deployment; the seismic survey is acquired when the cable is stationary during the normal operation sequence of the other logging services, such as pressure measurement and fluid sampling stations, coring points, calibration of nuclear magnetic resonance (NMR) tools, and plug setting. Whether the objective of the survey is first-time arrivals for basic velocity calculation and sonic corrections (checkshot) or full waveforms to extract a reflectivity series for well-tie analysis (VSP), the acquisition time is essentially the same: minimal.
Dual portable airgun tanks (PATs) were used for this operation to facilitate the deployment of airguns for a land operation. Excellent hDVS data can be efficiently acquired with the full range of Schlumberger seismic sources, including airguns and vibroseis units.