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Title: Analysis of four-component seafloor seismic data for seismic anisotropy
Author: Yuan, Jianxin
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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Interest in converted waves (C-waves) has been growing significantly in recent yeas due to the advent of four-component (4C) ocean-bottom-cable (OBC) seismic recordings. This has changed the way geophysicists obtain fluid and lithology information about hydrocarbon reservoirs through joint P- and converted-wave analysis. Since 4C OBC surveys use conventional air-gun sources, which generate P-waves only, the shear-waves recorded by the 4C sensors on the ocean bottom are mode-converted shear-waves. The main focus of this thesis is to find ways to process and understand these mode-converted shear-waves in the presence of seismic anisotropy which is common in marine sediments. To this end, I examine and model the data characteristics of 4C seismic data, review the basic theory of converted-wave processing, develop new kinematic theories for converted-waves propagating in anisotropic, inhomogeneous media, and apply these new methods to field 4C data. I focus on two types of anisotropy: transverse isotropy with either a vertical (TIV) or horizontal (TIH) axis of symmetry. As an emerging technology, the characteristics of 4C seismic data have not been fully understood, and there are many acquisition related problems yet to be solved. The characteristics of 4C seafloor data have been studied by field data analysis and by synthetic modelling. I have found: 1) the water-column reverberations in the vertical geophone are much weaker than those in the hydrophone, because of the different sensor responses to the source- and receiver-side multiples; 2) the presence of a low shear-wave velocity gradient in the seabed prohibits P-to-S conversion, and this implies that most shear-waves recorded in 4C data are converted at deep reflector; 3) due to current sensor design, there is a shear-wave energy leakage from the inline horizontal geophone to the vertical geophone, resulting in geophone coupling problem. I have also studied the problem of sensor orientation and presented geophone orientation algorithms for both gimballed and non-gimballed geophone systems.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available