David W. Bell

Seismic imaging of steeply dipping geologic interfaces

A method for determining the location of steeply dipping subsurfaces includes acquiring seismic reflection data, identifying select data which has characteristics indicating that the acoustic pulses which it represents have been reflected from a substantially horizontal interface and a steeply dipping interface, analyzing the select data to locate the steeply dipping interface and displaying the analyzed data.

Temperature variation of the acoustic properties of laboratory sediments

The compressional wave speed and attenuation and the shear wave speed and attenuation of unconsolidated artificial laboratory sediments have been measured as a function of temperature. No overburden or pore pressure in excess of that found at a few centimeters depth was applied. The compressional wave speed of the sediment was found to vary approximately as would water with a slight increase in the slope of the curve of the sediment over that of water. Shear wave speed appears to be independent of temperature within the accuracy of the measurement. Attenuation of both types of acoustic waves also appears to be independent of temperature. [Work supported by the Office of Naval Research.]

Common-offset depth migration as a velocity analysis tool

We imaged the Marmousi dataset using an efficient Kirchhoff prestack depth migration algorithm combined with a layer-stripping velocity analysis technique.

Shear and Compressional-Wave Surface and Downhole Tests in Southern Louisiana: ABSTRACT

Shear- and compressional-wave seismic tests using the Vibroseis system were performed near a well in south-central Louisiana to study acquisition, processing, and interpretation problems typically encountered in low-velocity, relatively uncompacted Gulf Coast sediments. The primary objectives envisioned for these tests were to improve S-wave data quality by studying surface noise patterns to optimize source and receiver arrays, provide a direct correlation of P- and S-wave seismic data by using vertical seismic profiles (VSP), and measure the decay of P- and S-wave seismic energy with depth by using a downhole geophone. To achieve these objectives, an expanding reflection profile (ERP), a walkaway noise analysis, and a VSP were recorded with both S- and P-wave sources. The S-wave ERP shows reasonable data quality although it was very band-limited (5-12 Hz). In contrast, the P-wave data quality is excellent. The difference in data quality is primarily due to strong, source-generated End_Page 465------------------------------ noise from the S-wave vibrators. Time-depth data available from the S- and P-wave VSPs were used to convert the time sections to depth, and hence provide the best visual tie of common reflecting horizons. The accuracy of the ties is mainly limited by the poor signal-to-noise ratio and narrow bandwidth of the S-wave data. Finally, energy decay measurements from first breaks on VSP data show that S waves have a higher loss than P waves in the near surface. However, below 3,000 ft (915 m), the slopes of the energy decay curves are similar, thus implying S-wave data quality will not deteriorate faster than P-wave data quality at greater depths. End_of_Article - Last_Page 466------------