In this thesis, I characterize the elastic properties, i.e., P- and S-wave velocities, of a hydrated structure present at the Blake Outer Ridge, offshore the southeast coast of the United States, using AVO analysis and modeling. I show how these properties can be related to the possible internal structure of the hydrated sediment by assuming physical rock models. Furthermore, I provide a theoretical tool for estimating the amount of hydrate present without prior well-log information.
Chapter 2 addresses the seismic data used in this study and the true-amplitude processing applied to them prior to AVO analysis. The actual AVO inversion and modeling is subsequently discussed in Chapter 3. The goal is to use AVO as an indicator of free gas underneath the hydrate and to delineate the behavior of P-wave and S-wave velocities across the BSR. A lot of the work described in Chapter 2 and 3 was originally performed with David Lumley and can be found in Ecker and Lumley (1993, 1994a,b). Subsequently, Chapter 4 provides a tool for quantifying the amount of gas hydrate and gas near the BSR, by linking physical rock models to the estimated interval velocities. Using three different possible schemes of hydrate deposition in the pore space, this results in different estimates depending on the used model. Since the use of only acoustic velocity cannot uniquely differentiate between the different models of hydrate deposition, Chapter 5 combines the rock physics models and seismic AVO analysis in order to obtain the internal hydrate structure. The work presented in Chapter 4 and 5 was performed in collaboration with Jack Dvorkin and Amos Nur from the Stanford Rock Physics Group and can be found in Ecker et al. (1997, 1998). Preliminary results are given in Ecker et al. (1996a,b).