Project Goal
The goal of NETL's gas hydrate numerical simulation studies is to obtain pertinent, high-quality information on the behavior of gas hydrates in their natural environment under either production (methane gas extraction) or climate change scenarios. This research is closely linked with NETL's experimental and field studies programs to ensure the validity of input datasets and scenarios.

Project Performers
Brian Anderson, IAES Fellow (West Virginia University)
Kenneth Jordan, NETL/IAES Fellow (University of Pittsburgh)
Hao Jiang (University of Pittsburgh, Post doctoral researcher)
Guozhen Gao (University of Pittsburgh, Graduate research assistant)
Revati Kumar (University of Pittsburgh, Post doctoral researcher)
Eugene Myshakin, NETL/Parsons
Isaac Gamwo, NETL Office of Research and Development
Robert Warzinski, Research Scientist – NETL Office of Research and Development

Project Locations
Pittsburgh, PA, and Morgantown, WV

Project Description
NETL ORD and the virtual Institute for Advanced Energy Studies (IAES) conduct advanced numerical simulations to better understand the response of gas hydrates to changes in environmental conditions. NETL’s numerical modeling includes studies conducted at the molecular scale (MDS, or molecular dynamics simulations, where the forces and motions of thousands of individual molecules are computed over timescales of nanoseconds); at the pore scale using thermodynamic and kinetic equations to describe gas hydrate reservoir response around a single bore-hole; to field-scale simulations that predict gas hydrate reservoir behavior over time-scales of decades. In addition, NETL-ORD will continue to lead the effort to compare numerical modeling capability within the ongoing International Code Comparison effort. Please see our web-page dedicated to that effort.

Reservoir-scale modeling: NETL has developed expertise in the operation of a variety of reservoir simulators, including the TOUGH+HYDRATE simulator, NETL's open-source code HydrateResSim, and the commercial model CMG STARS. Simulations currently focus on modeling gas hydrate reservoir response to both pressure and thermal stresses. In addition to field-scale simulation, NETL conducts laboratory scale simulation to determine how best to design experiments to validate observations made on larger scale simulations; e.g., secondary gas hydrate formation during depressurization-based production of Class 3 hydrate formations (those with no subjacent free gas or water). The simulators are also being used to evaluate the control of reservoir heterogeneity in porous medium in terms of hydrologic and thermal properties, e.g., hydrate saturation, permeability, porosity, thermal conductivity, and heat capacity, on various gas hydrate production scenarios.

In addition to model operation, NETL is providing improvements to these simulators by examining the fundamental relationships and processes within the codes. The focus of the current effort is to generalize Darcy’s law to account for accelerating and decelerating flows near the well bore and in fractures where the Reynolds number exceeds one (non creeping flows). The improved model should adequately analyze flow in porous media where the fluid moves toward a perforation in the well casing and then into the well.

In addition to production modeling, NETL is working to develop an initial economic modeling framework for methane hydrate production. Current drilling and production cost estimates derived from existing and previous well tests are being incorporated along with estimates for transportation costs and market variables. The model will include learning curves developed for new technology.

Molecular Dynamics (MD) simulations: NETL is conducting MD simulations with the goal of providing improved models and process descriptions for incorporation into pore and field-scale simulators. Several initiatives based in MD simulation are underway, including:

• Development of a new model to account for non-ideal behavior of the hydrate phase due to lattice expansion and molecular asymmetry. Simulations are being integrated into a thermodynamic model for improved prediction of hydrate phase equilibria. Simplified correlations that describe these results will be sought for incorporation into reservoir simulators.
• Improved understanding of gas hydrate metastability. This research is directed at a better understanding of hydrate induction time, self-preservation, and secondary hydrate formation and its control in hydrate production scenarios.
• Investigation of the impact and control various mineral phases present in natural sediments have on the gas hydrate formation and dissociation processes.
• Simulating the impact of small dissociation and formation driving forces on gas hydrate stability. The intent of this work is to determine the limiting factors to hydrate dissociation with respect to pressure, temperature, and dissolved gas concentration under stresses consistent with those from ongoing natural changes in the environment, including climate change.
• Study of the effect of various degrees of clathrate cage occupancy on the rate of methane hydrate lattice destruction. Current reservoir simulators utilize equilibrium models that assume destruction is instantaneous; however, initial results show that the kinetics of the methane hydrate decomposition reaction affects the mass balance across the decomposing hydrate. Changes in the mass balance might cause a shift of the thermodynamic equilibrium toward hydrate reformation owing to flow of mobile phase through areas with still dissociating hydrate and, thus, influence gas production at a well.
• Modeling the details of gas hydrate crystal growth after initial nucleation takes place. Currently it is not clear how the methane hydrate crystal build-up occurs; is it immediately converted into the sI structure or does it pass through preliminary stage(s) characterized by different unit cell configurations. Rates of hydrate formation are being determined using multiple trajectory runs at different driving forces.

Accomplishments

• Established the importance of water polarizability in the structural, spectroscopic, and thermodynamics properties of methane hydrate.
• Completed the first simulations of the thermal conductivity of methane hydrate using the non-equilibrium MD (NEMD) method:
  • Demonstrated that for T = 50 K, the methane molecules have almost no impact on the thermal conductivity
  • Demonstrated that explicit inclusion of polarization causes a ~two-fold reduction of the thermal conductivity, improving agreement with experiment
• Carried out simulations of methane hydrate decomposition
  • Provided clear-cut evidence for persistence of partial hydrate structure in the liquid phase and for reformation of the hydrate surface
• Extended our thermal conductivity simulations to Xe hydrate and CO₂ hydrate
  • Revealed that there are important differences between CO₂ hydrate and methane and Xe hydrate
• Carried out the first lattice dynamics simulations of methane hydrate
  • Showed that there are fundamental differences between ice and methane hydrate in that optical modes play a much greater role in the thermal conductivity of the latter
  • Appears to be related to the greater localization of phonons in methane hydrate

Communication and Outreach
Organized a Telluride Science Research Center (TSRC) workshop in Aug, 2008 that brought together ~25 of the world’s experts in hydrates.

Results presented by five members of our team (E. Myshakin, Hao Jiang, Brian Anderson, Robert Warsinski, Kenneth Jordan)

Current Status
The project is currently funded through end of FY2008.

DOE Fiscal Year 2008 Contribution: $839,200.

Additional Information:
In addition to the information provided here, a full listing of project related publications and presentations as well as a listing of funded students can be found in the Methane Hydrate Program Bibliography [PDF].

2008 Hydrate Peer Review [PDF-2.12MB]

Publications

Anderson, B., et al., Analysis of Modular Dynamic Formation test results from the Mt. Elbert-01 stratigraphic test well, Milne Pt., Alaska [PDF] ; Proceedings, 6th International Conference on Gas Hydrates (ICGH-2008), Vancouver, BC, July 7-11, 2008.

Wilder et al., An international effort to compare gas hydrate reservoir simulators [PDF]: Proceedings, 6th International Conference on Gas Hydrates (ICGH-2008), Vancouver, BC, July 7-11, 2008

Anderson. B., and the International Gas Hydrate Code Comparison Group, International Methane Hydrate Code Comparison Project Simulates Relevant Problems: Fire in the Ice Newsletter, U.S. DOE – Office of Fossil Energy, Winter 2007 [PDF], p. 5-7.

Anderson. B., and the International Gas Hydrate Code Comparison Group, Analysis of Pressure Test Data From the “Mount Elbert” Gas Hydrates Well: Fire in the Ice Newsletter, U.S. DOE – Office of Fossil Energy, Spring 2008 [PDF]. 10-12.

Jiang, H., Jordan, K., Taylor, C., 2007. Molecular Dynamics Simulations of Methane Hydrate using Polarizable Force Fields, J. Phys. Chem. B, 111, 6486-6492.

Jiang, H., Myshakin, E., Jordan, K., Warzinski, R., in press, Molecular Dynamics Simulations of the Thermal Conductivity of Methane Hydrate, J. Phys. Chem.

Myshakin, E., Jiang, H., Warzinski, R., Jordan, K., in review, Molecular Dynamics Simulations of Methane Hydrate Decomposition", J. Phys. Chem.

Myshakin, E., Gamwo, I., Zhang, W., Warzinski R., in review, Numerical Studies of Thermal Stimulation Effects on Methane Production Induced by Depressurization in a Reactor Containing Hydrate-bearing Porous Media, J. Petrol. Sci. Eng.