Date of Award

2016

Document Type

Open Access Thesis

Department

Earth and Ocean Sciences

Sub-Department

College of Arts and Sciences

First Advisor

Camelia C. Knapp

Abstract

Seismic imaging is recognized as the most cost effective method for identifying the presence of gas hydrate resources. The base of the gas hydrate stability zone is recognized by the presence of regionally extensive bottom simulating reflectors (BSR). However, in some areas such as the Gulf of Mexico, regionally extensive BSRs are not found. In such cases, an understanding of the thermobaric conditions may be used to determine the location of gas hydrates and the base of the gas hydrate stability zone. The aim of this research is to combine seismic velocity analysis and thermal modeling to predict the base of the hydrate stability zone. As a case study, we apply this modeling to the extensively documented site at Woolsey Mound, MC-118, Gulf of Mexico.

Woolsey Mound, and much of the Gulf of Mexico, has been greatly affected by salt tectonics. Multiple seismic and CHIRP surveys have been collected at Woolsey Mound, but the base of the gas hydrate stability zone has been elusive due to the complexities associated with the presence of salt. The velocity analysis and previous studies on the sedimentary environment were the basis to derive the thermal and salinity conditions. Data from the heat flow survey provide an upper boundary condition at the sea floor in order to create a more accurate thermal model; the velocity model helped accurately place the salt diapir within the mound system. Hydrate phase equilibrium models were used to estimate a thermobaric model for Woolsey Mound. Using two different salinity gradients, the base of the gas hydrate stability zone was found to be located within 70 m of the seafloor with a salt concentration up to 90% at the shallowest point of the salt diapir, and 120 m of the seafloor with a salt concentration up to standard temperature and pressure conditions of salt (of approximately 56%) at the shallowest point of the salt diapir. This study provides a preliminary look at how the temperature and salinity affect the depth at which gas hydrates are stable over a three dimensional area at Woolsey Mound, MC-118.

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