Overview of Borehole Seismic Methods
There are fundamental physical reasons why borehole seismic techniques can provide potentially better answers than conventional surface seismic techniques. There is a progression in both complexity and benefits from check shot and synthetic seismogram to vertical seismic profiles (VSP), three‑component VSP, offset VSP, and extrapolation and description of lithologic parameters into the geologic formations surrounding the borehole. Presently VSP's are run in wells to aid in the correlation of surface seismic data. Borehole velocity surveys, commonly called check shot surveys, are often expanded into VSP's since additional acquisition costs are relatively small.
Synthetic seismograms have traditionally been used to correlate surface seismic sections. Like all theoretical models, synthetic seismograms suffer from the simplifying assumptions that go into the model. An approximate fit to surface seismic lines is often obtainable. However, synthetic seismograms offer an important link in trying to understand the seismic tie to the well log. An example of a synthetic seismogram is shown in figure 1
Figure 1. Correlation between crosshole survey, velocity log synthetic seismogram, and surface seismic reflection section.
The pages found under Surface Methods and Borehole Methods are substantially based on a report produced by the United States Department of Transportation:
Wightman, W. E., Jalinoos, F., Sirles, P., and Hanna, K. (2003). "Application of Geophysical Methods to Highway Related Problems." Federal Highway Administration, Central Federal Lands Highway Division, Lakewood, CO, Publication No. FHWA-IF-04-021, September 2003. http://www.cflhd.gov/resources/agm/