The National Methane Hydrates R&D Program
DOE/NETL Methane Hydrate Projects
|Controls On Methane Expulsion During Melting Of Natural Gas Hydrate Systems
||Last Reviewed 6/24/2013
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 updip 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).
University of Texas at Austin, Austin, TX 73713-7726
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 determine the magnitude of these fluxes. Previous efforts to simulate hydrate formation and disassociation have shown that coupling all physical processes is critical to understanding the macro-scale process of hydrate melting.
Equilibrium thermodynamics will be coupled with conservation of mass (for methane, water, salt) and 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.
Researchers have initiated a 1-D simulation of gas hydrate dissociation in laboratory controlled conditions. A thermistor string for use in an experimental device was developed and preliminary simulations of gas flooding were performed. A 1-D simulation of gas hydrate dissociation in natural systems was performed using Buckley-Leverett equations to set the parameters to achieve the experimental goals.
Researchers examined in situ hydrate deposits with petrophysical approaches to determine the in situ salinity, pressure, and temperature and to determine the phase stability of different marine hydrate systems. High salinities in a number of locations, resulting in a stable gas phase within regions normally interpreted to lie within the hydrate stability zone, have been documented.
Current Status (June 2013)
Researchers are modifying and integrating existing dynamic models of hydrate formation based on phase stability and transport of mass and energy to be applicable to hydrate melting. The project team has modified their existing 1-D code to enable input of initial conditions that reflect realistic hydrate concentrations. The code was modified to allow for boundary conditions that apply changes in surface temperature and pressure through time, and the team is now simulating, in one dimension, the melting of in situ hydrate deposits due to temperature change.
The team will next apply the modified codes to laboratory-scale experiments. Researchers will run laboratory experiments to simulate the melting of hydrate in situ.
Project Start: October 1, 2012
Project End: September 30, 2015
Project Cost Information:
DOE Contribution: $1,170,806
Performer Contribution: $311,000
NETL – John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
University of Texas at Austin – Peter Flemings (email@example.com or 512-475-9520)
Quarterly Research Performance Progress Report [PDF-271KB] - Period ending 12-31-2012