DE-FE0010141

Goal
The overall objective of the project is to investigate hydrate system dynamics beneath seafloor mounds—a structurally focused example of hydrate occurrence at the landward extreme of their stability field—in the northern Gulf of Mexico. Researchers will conduct observatory-based in situ measurements at Woolsey Mound, MC118 to:

1. Characterize (geophysically) the sub-bottom distribution of hydrate and its temporal variability and,
2. Contemporaneously record relevant environmental parameters (temperature, pressure, salinity, turbidity, bottom currents, and seafloor microseismicity) to investigate possible links to climate variation.

These objectives will be achieved through scientific studies to:

• Employ the Direct Current Resistivity (DCR) method as a geophysical indicator of hydrates
• Identify hydrate formation mechanisms in seafloor mounds
• Detect short-term changes within the hydrate system
• Illuminate relationships/impacts of local oceanographic and microseismic parameters on the hydrates system and, indirectly, the benthic fauna
• Monitor the fluid/hydrate motion and seafloor instability that these changes might produce

Performer
The University of Mississippi – Center for Marine Resources & Environmental Technology (CMRET), University, MS 38677

Collaborators
Baylor University, Waco, TX 76798
Specialty Devices, Inc., Wylie, TX 75098

Background
Seafloor mounds represent one of the most diverse and least understood settings in which hydrates are found (Ahron, et al., 1992; Roberts and Aharon, 1994). Hydrate within seafloor mounds occurs as veins, nodules, and angular clasts encased in deformed, fine-grained sediment. It has also been found as massive outcroppings on the seafloor and as slabs of hydrate exposed above the seafloor. Hydrate-bearing mounds occur in water depths greater than 330m, worldwide, in association with a variety of other seafloor features including methane seeps (Crutchley et al., 2010), cold-seeps (Barnes et al., 2010), pockmarks (Chand et al., 2008), and gas chimneys.

Currently, hydrate-bearing mounds make better candidates for study than non-mound related hydrate within deformed muds, in part because mounds stand out on industry seismic data. The U.S. Bureau of Ocean Energy Management (BOEM) has used available industry data to identify over 2,300 potential hydrate-bearing mounds in the northern Gulf of Mexico. This project will focus on hydrate within seafloor mounds because the structurally-focused methane flux at these sites likely causes hydrate formation and dissociation processes to occur at higher rates than at sites where the methane flux is less concentrated. Furthermore, because the hydrocarbon flux at hydrate-bearing mound sites is structurally focused, these mounds may represent the exceptional case in which methane (and other hydrocarbon gases) occurs in three phases: solid hydrate, free gas, and dissolved in pore fluids. This three-phases equilibrium is very sensitive to even small environmental changes and likely causes hydrate formation and dissociation to occur at higher rates than at sites where the methane flux is less concentrated (Liu and Fleming, 2007). Hence, hydrate-bearing mounds represent the best chance of observing hydrate system dynamics in action.

Impact
Hydrate within seafloor mounds, and deformed marine muds in general, is the most likely form of marine hydrate to undergo rapid dissociation—leading to the potential release of large volumes of methane into the atmosphere—when some climatic trigger point is reached. Reliable estimates of the global volumes of methane in this setting and the conditions under which dissociation occurs are needed in order to assess the potential role shallow marine hydrate may play in climate change. This project, if successful, will shed new light on these issues by tying hydrate dynamics to oceanographic parameters that derive from and impact climate change.

Accomplishments
New project awarded on October 1, 2012

Current Status (January 2013)
In the first phase of the project, existing geophysical data will be reprocessed, analyzed, and interpreted to select target locations at Woolsley Mound. Two primary and two alternate targets will be selected based on regions that are most likely to show the presence of hydrate in the shallow subsurface (<75m) and show change in hydrate volume over time. Researchers will also reconfigure the resistivity instrument for long-term deployment and autonomous operation to monitor temporal changes in the near-bottom hydrocarbon system. Reseachers will then conduct a research expedition to deploy the monitoring instuments at Woolsley Mound for the first of two six-month periods.

Project Start: October 1, 2012
Project End: June 30, 2015

Project Cost Information:
Phase 1 – DOE Contribution: $590,561, Performer Contribution: $147,648
Phase 2 – DOE Contribution: $436,853, Performer Contribution: $109,213
Phase 3 – DOE Contribution: $184,672, Performer Contribution: $62,607
Planned Total Funding – DOE Contribution: $1,212,086, Performer Contribution: $319,468

Contact Information:
NETL - Skip Pratt (skip.pratt@netl.doe.gov or 304-285-4396)
The University of Mississippi - Center for Marine Resources & Environmental Technology (CMRET) – Carol Lutken (clutken@olemiss.edu or 662-915-5598)

Additional Information

Research Performance Progress Report [PDF-872KB] January - March, 2013