dc.contributor.advisor | Sen, Mrinal K. | en |
dc.contributor.advisor | Stoffa, Paul L. | en |
dc.creator | Kumar, Dhananjay | en |
dc.date.accessioned | 2008-08-28T22:08:06Z | en |
dc.date.available | 2008-08-28T22:08:06Z | en |
dc.date.issued | 2005 | en |
dc.identifier | b59923441 | en |
dc.identifier.uri | http://hdl.handle.net/2152/1598 | en |
dc.description | text | en |
dc.description.abstract | Multicomponent seismic data can be used to derive P- and S-wave
velocity structures of the subsurface, which can be used further to estimate rock
and reservoir properties. Most seismic analysis methods and algorithms assume
that the earth is isotropic. In many geologic situations, however, sedimentary
rocks exhibit anisotropic behavior, and the isotropic assumption will introduce
errors in the estimates of the elastic properties of the subsurface. With the goal of
analyzing multicomponent seismic data from complex regions (which may show
anisotropic behavior), I have developed new algorithms for 1) seismic modeling
based on a ray-Born approximation and 2) traveltime computation in tilted
transversely isotropic media based on Fermat’s principle. This new traveltime
computation algorithm is tested on prestack depth migration of a physical model
dataset. Such algorithms are essential for estimating subsurface rock properties in
complex areas such as the Hydrate Ridge area, offshore Oregon.
viii
I participated in the acquisition of multicomponent seismic data (summer
2002), at the Hydrate Ridge of the Cascadia convergent margin. The primary goal
of the experiment was to map the gas hydrates and free gas, and to understand the
mechanism of fluid migration. Gas hydrate is an ice-like substance that contains
low molecular weight gases (mostly methane) in a lattice of water molecules. Gas
hydrates and free-gas are generally detectable with seismic methods because the
seismic velocity increases in the presence of gas hydrates, and it decreases in the
presence of free-gas. My analysis results in estimates of P- and S-wave interval
velocities and anisotropic parameters with the final goal of relating these
parameters to the presence and quantification of gas hydrate and free gas. I
performed interval velocity analysis in the τ-p (intercept time - ray parameters)
domain following three main steps: 1) P-wave velocity analysis, 2) P- to S-wave
(converted PS-wave) event correlation, and 3) S-wave velocity analysis. P- to Swave
event correlation is done using synthetic seismograms and traveltime tables.
Seismic velocities are correlated to gas hydrate and free gas saturation using a
Modified Wood equation. I find that Hydrate Ridge is heterogeneous and is
weakly anisotropic (maximum of 10%) in some regions caused possibly by the
hydrate veins. The P-wave velocity is more sensitive to the saturation of gas
hydrates (maximum of 7% of rock volume) and free gas than the S-wave velocity.
The S-wave velocity does not show an anomalous increase in the hydrate-bearing
sediments. Thus, I conclude that hydrate does not cement sediment grains enough
to affect shear properties. It is more likely that the hydrates are formed within the
pore space in this region. | |
dc.format.medium | electronic | en |
dc.language.iso | eng | en |
dc.rights | Copyright is held by the author. Presentation of this material on
the Libraries' web site by University Libraries, The University of Texas at Austin was made
possible under a limited license grant from the author who has retained all copyrights in
the works. | en |
dc.subject.lcsh | Seismology--Oregon--Hydrate Ridge | en |
dc.subject.lcsh | Geology--Oregon--Hydrate Ridge | en |
dc.title | Analysis of multicomponent seismic data from the Hydrate Ridge, offshore Oregon | en |
dc.description.department | Geological Sciences | en |
dc.identifier.oclc | 61387340 | en |
dc.identifier.proqst | 3174477 | en |
dc.type.genre | Thesis | en |
thesis.degree.department | Geological Sciences | en |
thesis.degree.discipline | Geological Sciences | en |
thesis.degree.grantor | The University of Texas at Austin | en |
thesis.degree.level | Doctoral | en |
thesis.degree.name | Doctor of Philosophy | en |