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Recently, 3-D four‐component marine ocean‐bottom cable (OBC) data has come into broad use for a variety of applications. However, understanding how these new components and their associated acquisition and processing coordinate systems are related to the vector wavefield has become a challenging task for the exploration industry. The compressional wavefield (P-wave) is obtained from the pressure response of the hydrophone plus the particle‐motion response from the vertical geophone. A converted P-wave to shear wavefield (PS-wave) is obtained from two horizontal geophone components oriented in an acquisition coordinate system of in‐line and cross‐line particle motion.

It is well established that similar vertical wavelength ranges must be preserved in multicomponent data and that wavelengths of P- and S-waves must match in order to sample reflectivity in an equivalent manner. Conversion of a wavefield to another time or depth domain is described by transformation functions that depend on average VP/VS ratios and velocity. Although these functions align corresponding stratigraphic events of different wavefields, they distort the seismic wavelet because global average velocity properties are independent of local interval properties that define wavelength. In this study we develop a theory of velocity-based wavelet corrections for domain transformations, which are expressed as functions of interval and average VP/VS and velocity, to match wavelength of multicomponent wavefields. We examine the effects for both land and marine data examples and find that land surveys are affected more than marine, and may require spectral broadening of the wavelet. Data from the Marcellus shale in northeast Pennsylvania, USA, shows significant bandwidth improvements for C-waves when wavelet corrections based on velocity match their wavelengths with P-waves. Application of these wavelet corrections should benefit registration fidelity, joint AVO/A (offset and azimuth) inversions and attribute analyses.

In multicomponent seismic reflection surveys, surface and near‐surface effects can severely deteriorate the quality of reflection data. Such effects are more pronounced on shear‐wave than on compressional‐wave profiles. Amplitude anomalies, statics, and strong coherent source‐generated noise (i.e., surface waves) are often associated with inhomogeneous, poorly compacted near‐surface sediments of the weathering layer. The magnitude of such effects increases when sources and receivers are deployed at or near the surface in proximity to such inhomogeneities. Near‐surface effects can be investigated with respect to their depth of occurrence by burying seismic sources and/or receivers at various depths below the inhomogeneous weathering layer. In this context, an experiment was conducted to collect multicomponent seismic field data on a borehole‐controlled test site in east Texas. Data were recorded on three‐component surface and buried receivers using a full‐vector wavefield surface source. Although the geology appears simple, results of modeling one or two components of the field data with synthetics yields nonunique estimates of elastic parameters. Effects of anisotropy and heterogeneities are better identified and estimated with full‐wavefield surface and buried receiver observations. Single fold data from buried receivers yield reflection events with higher signal‐to‐noise ratio than 30‐fold CDP surface data previously acquired in the same area.

In this study we investigate methods of elastic-wavefield interferometry to obtain P- and S-wave velocity information from the 3D P-wave vibrator VSP atWamsutter Field inWyoming. Wamsutter field consists of naturally fractured tight gas sand reservoirs wh

Recently, 3-D four-component (4-C) marine ocean-bottom cable (OBC) data has come into broad use for a variety of applications.

For both marine and land data inconsistent coupling of the three geophone components can prevent a proper combination for vector wavefield processing. On the ocean bottom it is more difficult than on land to plant geophones effectively, and it is expensive to bury cables or plant them with robotic devices to ensure good coupling.

Historically, observations of shear-waves in the marine environment began with the work of oceanographic institutes in their investigations of ocean-crust velocity structure.

Shot-generated coherent noise, in the form of dispersive surface waves and trapped modes, is a significant problem corrupting seismic data.

Explicit finite-difference migration is attractive because it can be easily extended to 3-D depth migration (Blacquiere et al., 1989) and produces accurate, high-dip images in the presente of strong, lateral velocity variations using stable wavefield extrapolation filters (Holberg, 1988 ; Hale, 1991a). After Hale (1991b) introduced the application of these filters via McClellan transformations there has been much effort to improve accuracy. This paper discusses the advantages and limitations of various transformation and filter structures presented in the literature and proposes an optimal approach.

Shear-wave particle motion directions measured in vertical seismie profiles (VSP) are very sensitive to anisotropic properties of the medium; however, in the case of compressional waves this is not true (Crampin 1981). Analyzing polarization diagrams (holograms) to measure these directions can be inaccurate because individual 3-component geophones are subject to interference from ambient noise and ot her coherent signals. An alternative is to investigate polarization characteristics along wavefronts using multicomponent Radon transforms.

Near-offset vertical seismic profiling (VSP) is an established technique to obtain interval velocities for lithology characterization, time-to-depth calibrations, and seismic data processing. Unfortunately, these velocities are often insufficient to distinguish lithology types and can disagree with surface seismic stacking velocities. Multiple-source offset VSPs provide additional travel time information for calculating interval anisotropic velocities that can help discriminate lithology. In this paper, a technique is developed for computing transversely isotropic phase velocities over intervals less than the dominant seismic wavelength. Independent estimates of vertical and horizontal slowness are made for each receiver depth and source offset pair. These provide the magnitude and direction of phase velocity for calculating the in situ elastic properties of a transversely isotropic medium. This technique requires the assumption of lateral homogeneity because horizontal slowness components are related to surface properties between sources and not to rock properties between receivers at depth. Factors that violate this assumption such as source elevation differences and dipping layers are evaluated with synthetic data. Six impulsive source P wave offset VSPs in a 663-m well in east Texas are analyzed and a near offset SH wave vibrator VSP provides vertical shear wave phase velocities. Strong transversely isotropic velocity variations observed in the Tertiary and Cretaceous sediments penetrated by this well correlate with lithology types, suggesting that this technique is sensitive to local properties at the receiver. These results may not indicate exact intrinsic elastic properties and could be due in part to dipping layers, vertical heterogeneities, and unknown local surface variations. Percent “phase velocity” anisotropy appears to increase from 6 to 20% for P wave and 10 to 50% for SV wave with increasing amounts of calcareous material and shale in the rock. (Percentage anisotropy is defined as the ratio of the horizontal to vertical velocity for P waves and the ratio of velocity at 45° to vertical velocity for SV waves.) Sandstones and chalk exhibit the least amount of anisotropy, while the shales and calcareous shales exhibit the most.

A double gap of cylindrical proportional chambers has been designed and built for use with a large solid angle, modular NaI(Tl) array (The Crystal Ball). The chambers are constructed of three coaxial foam-epoxy shells, covered with an aluminum-mylar laminate. One of the high voltage cathodes in each chamber has been photo-etched to produce a pattern of stripes and precise position measurements of tracks passing transverse to the chamber axis are found by pulse height analyzing the shaped and amplified induced strip signals. Performance of the chamber using both the strip signals and the sense wire readout is presented. The design of both the signal handling electronics and the digital portions of the systems is discussed.

Relative excitation efficiencies are reported for the fluorescence at 173 nm in liquid xenon excited by 0.5 MeV electrons (β particle), 6 MeV alpha particles (α particle), and 90 MeV fission fragments (ff). Efficiencies at 173 nm are also reported for alpha particle and fission fragment excitation of high pressure xenon. Results are presented in the form of ratios which compare the fluorescent output per unit energy for excitation by the different particles. The β/α and α/ff ratios for liquid xenon are 1.25±0.5 and 3.5±1.2, respectively. For xenon at 2000, 3000, and 4000 Torr, the α/ff ratios are 0.60±0.25, 0.61±0.23, and 0.63±0.24, respectively.

We report the use of a 500 keV Van de Graaff proton accelerator to produce ?-rays in the range 4 - 18 MeV via nuclear reactions for the purpose of calibrating a large NaI(Tl) crystal array. Data analysis indicates an energy calibration to ~ 1% over this range.