Including higher order effects means including multiples.
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BG5.6 SUMMARY Shear-wave birefringence has long been associated with the presence of vertical fractures. A common method for identifying fractures in this manner has been from detection of shear-wave splitting in shear-wave VSPs. Such surveys exclude marine acquisition and are limited to regions where shear-wave sources are available. In this paper, a technique for measuring shear-wave birefringence from converted shearwaves in offset VSP data is described. Provided the propagation of the SV waves is nearly vertical, a parametric inversion method can be applied to the horizontal components from a multicomponent offset VSP survey which models the data in terms of three parameters: the fast shear polarization, and the fast and slow shear velocities.
The motivation was to investigate whether one may employ NMR, which is a fast, non-destructive analytical tool, to measure the effective porosity of lowpermeable shales. The latter porosity is relevant for possible correlations to permeability. Presently, log-derived porosities (neutron, density) tend to yield closer to the total porosity which may differ significantly from in shales. Core porosities may be determined by means of timeconsuming, destructive drying-up techniques, restricting the access to the cores. Our measured NMRporosities seem to agree with those attained by the loss of water.
BGl.2 SUMMARY Additionally, hydrophone receivers are adversely affected by receiver well tube wave phenomena and other fluid-borne noise . An essential requirement for both Vertical Seismic Profiling In contrast, previous development efforts have resulted in multi- (VSP) and Cross-Hole Seismic Profiling (CHSP) is the rapid station wall-locked receivers that are limited in their frequency acquisition of high resolution borehole seismic data. Additionally, full wave-field recording using three-component receivers enables response. Prior wall-locked systems suffer from two significant deficiencies; locking resonances around 200 Hz, and low downhole the use of both transmitted and reflected elastic wave events in the sample rates. To this end, an reported to date are better suited to applications where relatively advanced three-component multi-station borehole seismic receiver low frequency seismic energy ( 200 Hz) is propagated from system has been designed and developed by Sandia National Labs source to receiver.
SUMMARY We estimate velocity/frequency dispersion and attenuation in fully saturated rocks by employing the squirt-flow mechanism of solid/fluid interaction. In this model pore fluid is squeezed from thin soft cracks into surrounding large pores. Information about the compliance of the soft pore space at low confining pressures is extracted from high-pressure velocity data. The frequency dependence of squirt-induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space, and the characteristic squirt-flow length. These unknown parameters are combined into one expression which is assumed to be a fundamental rock property that does not depend on frequency.
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Summary Three well-known methods of wave analysis, each using rays, are considerd in order to develope a coherent whole. The goal is to help wave theorists to use the most appropriate method and even jump from one method to another conceptually. To give this paper a reasonable scope, attention has been restricted to a two layer model and to SH waves.
A realistic, reservoir-scale, 3-dimensional earth model of the lower Miocene (Fleming) sandstone reservoir sequence at Powderhorn field, Calhoun County, Texas has been constructed. We first mapped the detailed lithology of 250 m of stratigraphic section over an area of 16 by 11 km. Wireline logs from more than 110 wells provided the data for a detailed facies analysis of 14 sandy depositional units encased in 15 shale units. The average thickness of mapped sand units is 3-30 m. In six wells, porosity and shaliness were evaluated from density, neutron, and spontaneous potential (SP) logs. These parameters correlate well to acoustic and density logs values. Based on relationships from these wells, key rock properties were estimated from SP and resistivity logs in older wells with incomplete log suites. These properties were then interpolated between wells within a 13 by 9 km model area. Interpolation incorporated the facies analysis through a 2-dimensiona1, directional computer mapping algorithm.
Summary This paper analyzes tomographic crosswell reconstructions associated with 2-D and 3-D acoustic wave propagation in a steam front model. Results show a general agreement between 2-D and 3-D arrival times. Differences between 2-D and 3-D first arrival times are less than 1% on average. The velocity tomograms reconstructed from the 2-D and 3-D first arrivals are very similar and suggest that tomograms are valid even in the presence of 3-D effects in the recorded seismic data. The propagation of secondary phases show significant 3-D (out-of-the-plane) effects due to focusing by the the low velocity anomaly and suggests caution in the use of reflected and scattered arrivals in 2-D inversion.