DE-FE0010406

Goal
The project goal is to predict, given characteristic climate induced temperature change scenarios, the conditions under which gas will be expelled from existing accumulations of gas hydrate into the shallow ocean or directly to the atmosphere. When those conditions are met, the fraction of the gas accumulation that escapes and the rate of escape shall be quantified. The predictions shall be applicable in Arctic regions and in gas hydrate systems at the up dip limit of the stability zone on continental margins. The behavior shall be explored in response to two warming scenarios: longer term change due to sea level rise (e.g., twenty-thousand years) and shorter term due to atmospheric warming by anthropogenic forcing (decadal time scale).

Performers
University of Texas at Austin, Austin, TX 73713-7726

Background
The central hypothesis proposed is that hydrate melting (dissociation) due to climate change generates free gas that can, under certain conditions, propagate through the gas hydrate stability zone and vent at the seafloor. Gas venting through the regional hydrate stability zone is accomplished by alteration of the regional equilibrium conditions (creation of three phase conditions) by increased salinity and heat due to hydrate formation, gas fracturing, or a combination of both. This research will explore the controls on whether methane reaches the seafloor (or atmosphere) as the original hydrate deposit dissociates and what the magnitude of these fluxes are. Previous efforts in simulating hydrate formation and disassociation have shown that coupling all physical processes is critical to understanding the macro-scale process of hydrate melting.

Impact
Equilibrium thermodynamics will be coupled with conservation of mass (for methane, water, salt) and conservation of energy (accounting for the latent heat of formation of hydrate), with multiphase transport models in geologically heterogeneous sediments to simulate macro-scale behavior. Based on previous efforts, these models will illustrate important behaviors that have important first order controls on how degassing occurs during warming. This project includes laboratory experiments explicitly designed to (in)validate the models, which will illustrate how much confidence is warranted in the model predictions, greatly increasing their impact. Thus the technology to be developed in this project could provide an essential component of the portfolio of technologies and knowledge needed to understand the impact of climate change on hydrate degassing.

Accomplishments
New project awarded October 1, 2012

Current Status (January 2013)
Researchers are modifying and integrating existing dynamic models of hydrate formation based on phase stability and transport of mass and energy (Behseresht and Bryant, 2011a; Behseresht and Bryant, 2011b; Behseresht et al., 2008a; Behseresht et al., 2008b; Liu and Flemings, 2006, 2007) to be applicable to hydrate melting. In the coming months the project team will modify their existing 1-D code to enable input of initial conditions that reflect realistic hydrate concentrations, pore water salinities, etc. The code will be modified by applying boundary conditions to allow for the ability to supply changes in surface temperature and pressure through time. After completion of the code, the project team will apply the modified codes to laboratory-scale experiments and natural hydrate systems (such as sub-oceanic and Arctic sub-permafrost systems) for comparison.

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

Project Cost Information:
DOE Contribution: $1,170,806
Performer Contribution: $311,000

Contact Information:
NETL ? John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
University of Texas at Austin ? Peter Flemings (pflemings@jsg.utexas.edu or 512-475-9520)