Analysis of P and S Wave Vertical Seismic Profile Data From the Salton Sea Scientific Drilling Project

Abstract

As part of the Salton Sea Scientific Drilling Project at California State well 2–14, vertical seismic profile (VSP) data were collected from P and S wave sources at two distances from the well. Use of a three‐component geophone, along with rotation of the recorded data traces into a wave front‐based coordinate system, allows analysis of many aspects of seismic wave propagation properties around the well. Standard VSP analysis techniques were used to measure interval P and S wave velocities and to identify reflecting horizons both within and below the survey interval (from 455 to 1735 m). A reflection from below the survey interval, seen with both P and S sources, seems to be associated with a fractured reservoir near 2100 m. Indications of fracturing were observed, including vertical scattering of P waves from a zone near 915 m. Orthogonally polarized shear waves were generated at each offset to study anisotropy by travel time measurement and particle motion analysis of the shear wave arrivals. Three‐component particle motion analysis of shear wave arrivals was found to be effective for characterizing the subtleties in the S wave splitting throughout the various zones in the well. The SHt source (horizontal and transverse to the well) produced complicated, elliptical particle motion while the SV source (in‐line with the well)produced linear particle motion. The difference in linearity of particle motion from orthogonally polarized shear wave sources was unexpected and may be related to regional tectonics. Anomalous zones may be related to transition depths in the Salton Sea geothermal field. Travel time difference between SV and SH waves, while clearly observable, indicates only about 1% average anisotropy.

Microearthquake Study of the Salton Sea Geothermal Field, California: Evidence of Stress Triggering - Masters Thesis

“…This well is described by Elders and Sass (1988) and provides a significant context for analysis in this study. The primary lithologies encountered in State 2-14 are lacustrine shales and siltstones as well as bedded anhydrites.…”

Laboratory studies of the acoustic properties of samples from Salton Sea Scientific Drilling Project and their relation to microstructure and field measurements

“…A comparison of compressional wave velocities determined from the high gain full waveform acoustic log (FWAL, Paillet and Morin, this issue), vertical seismic profile (VSP, Daley et a!., 1987), and our measured core velocities is presented in Figure 10. All three velocities agree well with each other.…”

“…The two samples with velocities less than the VSP (910 and 1060) are probably due to local variations; they probably represent slower layers in the stratified column. The VSP velocities are averaged over a 60 m interval (Daley et a!., 1987) and thus failed to pick up the three thin, low velocity zones at around 1350, 1450 and 1500 m in depth. The VSP does show a decrease in velocity between 1410 and 1470 m, but as expected, does not have the depth resolution of the FWAL.…”

Monitoring underground gas storage in a fractured reservoir using time lapse vsp

“…A 40 Hz, 60 dB/octave low pass filter was applied to the data before the zero-offset time picking. The rotation angle analysis was done using P-wave particle motion eigenvalue analysis (Daley, et al, 1988). The resulting edited, correlated, rotated seismograms are shown in Appendix A.…”

“…Nine-component VSP'S (3 component sources and 3 component receivers) provide an excellent method of measuring shear-wave splitting , Daley, et al, 1988, Daley and McEvilly, 1990, Winterstein and Meadows, 1991.…”