Surface-to-borehole illumination of a high-velocity layer using marine VSP

Colin MacBeth, Enru Liu, Mark Boyd, Karen Sweeney

Research output: Contribution to conferencePaper

Abstract

Two marine walkaway VSP lines are recorded by three-component receivers positioned in a dolomite layer. The layer has a high seismic velocity relative to the surrounding rocks and may be fractured. The recorded wavefield is analysed to determine whether this acquisition is suitable to image details of the internal structure of the layer. The principal arrivals in the wavefield are a dominant horizontally refracted compressional wave with a smooth unbroken moveout, converted shear-waves from shallow reflectors, and reverberation of these converted shear-waves within the high velocity layer. Anisotropic analyses of the converted shear-waves estimate an overburden birefringence of 3% and a polarization direction consistent with the known NW-SE maximum compressive stress. Full-wave modelling of the recorded wavefield aids identification of the various arrivals and constrains the attenuation and anisotropic properties of the layer, which appears laterally uniform with the most satisfactory model possessing low attenuation but a birefringence of no more than 5%. If the layer is cracked, these results are diagnostic of evenly distributed cracks with a scalelength smaller than a fraction of a wavelength.

Original languageEnglish
Pages125-128
Number of pages4
DOIs
Publication statusPublished - 1994
Event1994 Society of Exploration Geophysicists Annual Meeting - Los Angeles, United States
Duration: 23 Oct 199428 Oct 1994

Conference

Conference1994 Society of Exploration Geophysicists Annual Meeting
Abbreviated titleSEG 1994
CountryUnited States
CityLos Angeles
Period23/10/9428/10/94

ASJC Scopus subject areas

  • Geophysics

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