ABSTRACT: Acquisition and In-Field Processing of a Vertical Seismic Profile (VSP) to Determine Horizontal Kickoff Angle and Depth
REBEC, TONY, and MARTY HALL, Halliburton Geophysical Services, Inc., Sugarland, TX
Vertical seismic profile (VSP) data are collected in a borehole for a variety of reasons. The simplest of VSPs, a checkshot, is done to acquire actual seismic velocities at the borehole from surface to particular geologic horizons at specified depths. This profile enables the geophysicist to calibrate his sonic log and to more correctly process and interpret his synthetic seismogram and/or his seismic data in the area near his well.
A zero offset VSP can be done for a variety of reasons, the most obvious of these being a direct time-to-depth (seismic time to borehole footage) correlation of each horizon location, also resulting in a seismic character identification of each horizon, and aiding in seismic section interpretation.
Other uses of the zero offset VSP can be as follows: (1) Predicting lithology below the target depth; (2) Improving seismic processing of the surface data through the use of a deconvolution operator designed from the VSP data; (3) Detecting and locating faults or stratigraphic features in or below the borehole; (4) Determinating fracture location and orientation
A far offset VSP can gather extremely accurate seismic data laterally away from the borehole; (5) Detecting and locating structural features (faults, intrusives, etc.); (6) Tracking and locating producing zones and reservoirs for development drilling; (7) Detecting and locating stratigraphic features (pinch-outs, sand lenses, channels, etc.).
This case study illustrates the use of far offset VSP to detect and locate features laterally away from the borehole, which aids in planning further drilling.