Preliminary Results Of A Seismic Borehole Test Using Downhgle Shaped Charges At The Doe Hanford Site

Geophysical site characterization studies can be important steps in the process of designing and<br>monitoring remediation at hazardous waste storage facilities. However, use of seismic techniques for<br>subsurface characterization at the DOE Hanford Site has been limited for several reasons. One reason<br>is the lack of borehole velocity control, which is valuable to the development of initial geologic<br>models and seismic data processing. Current drilling procedures result in steel-cased boreholes which<br>are poorly coupled to the surrounding sediments. In addition, these low-velocity sediments are highly<br>attenuative. Consequently, standard techniques to provide velocity control are not adequate. Both<br>Vertical Seismic Profiling (VSP) and reversed VSP (RVSP) surveys are currently being investigated<br>to provide velocity control and for subsurface imaging capabilities.<br>Recently a jet perforating gun was used to perforate a double-cased borehole in the 200 West Area.<br>During this operation, acoustic emissions were recorded from numerous depths to obtain velocity<br>control for a previous surface survey conducted in the same area. Both P- and S-wave data were<br>recorded simultaneously from multiple horizons using the DAS-1 seismograph and 3-component<br>geophones. The data were analyzed for a variety of uses besides velocity control. Signal attenuation<br>was studied as a function of source depth and offset distance to evaluate formation absorption while<br>vertical resolution was determined from the frequency spectrum.<br>Preliminary results indicate that adequate P-wave velocity control can be obtained even though the<br>near-surface sediments are very attenuative. However, we conclude that the perforating gun produces<br>little SH energy. Preliminary velocities indicate that reflection coefficients should be great enough to<br>use surface techniques. Results from the frequency study suggest that a swept source for both surface<br>and borehole surveys may be necessary to obtain required resolutions. Finally, signal attenuation as a<br>function of formation facies suggest that seismic techniques may be useful in mapping perched water<br>zones and for long term vadose zone monitoring.