Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Joel E Johnson

Second Advisor

David Divins

Third Advisor

Jo Laird

Abstract

Submarine methane-hydrate reservoirs represent an ephemeral reservoir of carbon on Earth that can contain economically important concentrations of methane. Turbidite sands in deepwater marine environments have been targeted by recent research because they contain sufficient primary porosity to host high saturations of methane hydrate within the temperature and pressure window of the gas-hydrate stability zone. Silty turbidite levee deposits, however, also contain sufficient primary porosity to host high saturations of methane hydrate and they may contain more organic carbon than sand to fuel methanogenesis. In this research I used laser diffractometry to measure the full grain-size distribution of 46 bulk and 51 organic-carbon-free methane-hydrate reservoir sediment samples collected with pressure cores from a turbidite channel-levee system in the Gulf of Mexico during the 2017 UT-GOM2-1 Hydrate Pressure Coring Expedition. My results characterize the reservoir into three silt-dominated lithofacies and show that each lithofacies is characteristic of a specific sub-environment of deposition (i.e., turbidity current, waning turbidity current, and inter-event sedimentation) within the channel levee system. The results also show that organic carbon in this reservoir resides predominantly in the fine sediment fraction of all three lithofacies. The implications of these results are that silt-dominated reservoirs may accumulate methane and methane hydrate via both short-range and long-range methane migration pathways. In the Gulf of Mexico setting examined here, deformation associated with salt diapirism promotes long-range migration pathways via faults, fractures, and dipping stratigraphic horizons that may help to explain the extremely high gas-hydrate saturations (up to 93% of pore volume) recovered in these pressure cores. The results presented in this research, coupled with recovered gas hydrate in the pressure cores suggests that silt-dominated channel levee environments may accumulate a significant quantity of methane hydrate through time and have important implications for the distribution of methane hydrate in marine sediments.

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