NETL ORD – Methane Hydrate Research - Numerical Simulation
Last Reviewed 09/16/2010
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.
Brian Anderson, IAES Fellow (West Virginia University)
Kenneth Jordan, NETL/IAES Fellow (University of Pittsburgh)
Guozhen Gao (University of Pittsburgh, Graduate research assistant)
Eugene Myshakin, NETL/URS
Yong Liu, NETL/URS
Isaac Gamwo, NETL Office of Research and Development
Robert Warzinski, Research Scientist – NETL Office of Research and Development
Pittsburgh, PA, and Morgantown, WV
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.
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.
Reservoir-Scale Modeling - Hydrate saturation of a fully heterogeneous reservoir in the Mt. Elbert C Unit after 180 days of depressurization at 2.8 MPa (see Anderson et al., 2010b).
Researchers have studied a geologic system based on the Mount Elbert, Milne Point, Alaska’s North Slope sub-permafrost hydrate deposit. In 2007 the U.S. Department of Energy, BP Exploration (Alaska), and the U.S. Geological Survey collected open-hole formation pressure response data at the “Mount Elbert” stratigraphic test well. Analysis of the wireline log data has confirmed that two (the “D”- and “C”-sand) hydrate-bearing sand reservoirs exist within the Sagavanirktok formation in the Mount Elbert Site. The test well obtained core, log, and fluid measurements. The measurements and samples collected during coring and drilling of the well has resulted in an extensive dataset which characterizes the reservoir and non-reservoir facies. Data such as, hydrate saturations, water content, porosity, density, permeability, and others were used to prepare a refined geologic model for the numerical simulation of the deposit.
The schematic of the Mt. Elbert hydrate deposit
The goal of this study was to investigate production scenarios which would result in high gas production rates sustained over tens of year periods. In particular our simulations take advantage of the close proximity of Unit D and C hydrate reservoirs in the Mount Elbert-01 Well. In addition, the simulations evaluated the effect of decreasing bottomhole pressure below the quadruple point on key characteristics of the reservoir during the late stage of production.
Hydrate saturation depicted in a cross-section of the deposit after 5 years of production. The wellbore is completed along the left side of the image
Uncertainty analysis of the gas production from a down-dip Prudhoe Bay hydrate reservoir depiction (Problem 7c) as described in Anderson, et. al, ICGH, 2008.
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.
- 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.
Molecular Dynamics Simulations - Electron density plot for an H2O - CO2 complex. Intermolecular potentials for this complex have been calculated via ab initio methods and accurate occupancy values have been determined. These potentials are being used in MD simulations to evaluate the mechanism of CO2 and CH4dissolution from hydrates into undersaturated water.
Snapshot at 13 nanoseconds of a methane hydrate dissolution simulation.
- 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
Presented at a number of national meetings including the Methane Hydrate Symposium at the 2009 ACS National Meeting in Salt Lake City, UT, the 2009 Fall AIChE Meeting in Nashville, TN, and the TOUGH Symposium in 2009.
Participating in the 2010 Gordon Research Conference on Natural Gas Hydrate Systems as discussion lead for Models Across Spatial Scales.
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)
The project is currently funded through end of FY2010.
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].
Anderson, B., Hancock, S., Wilson, S., Enger, C., Collett, T., Boswell, R., Hunter, R., 2010. “Formation pressure testing at the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Operational summary, history matching, and interpretations,” Marine and Petroleum Geology, Vol. 28, Iss. 2, Thematic Set on Scientific results of the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope, Pages 478-492, ISSN 0264-8172, doi: 10.1016/j.marpetgeo.2010.02.012.
Anderson, B.J., Kurhiara, M., Wilson, S.J., Pooladi-Darvish, M., White, M., Moridis, G., r Gaddipati, M., Masuda, Y., Collett, T.S., Hunter, R.B., Narita, H., Rose, K., Boswell, R., 2010. “Regional long-term production modeling from a single well test, Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope,” Marine and Petroleum Geology, Vol. 28, Iss. 2, Thematic Set on Scientific results of the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope, Pages 493-501, ISSN 0264-8172, doi: 10.1016/j.marpetgeo.2010.01.015.
Gamwo, I.K., Liu, Y, 2010. “Mathematical Modeling and Numerical Simulation of Methane Production in a Hydrate Reservoir,” Industrial Engineering & Chemical Research, 49 (11), pp 5231–5245.
Hunter, R.B., Collett, T.S., Boswell, R., Anderson, B.J., Digert, S.A., Pospisil, G., Baker, R., Weeks, M., 2010. “Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Overview of scientific and technical program,” Marine and Petroleum Geology, Vol. 28, Iss. 2, Thematic Set on Scientific results of the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope, Pages 295-310, ISSN 0264-8172, doi: 10.1016/j.marpetgeo.2010.02.015.
Wilson, S.J., Hunter, R.B., Collett, T.S., Hancock, S., Boswell, R., Anderson, B.J., 2010. “Alaska North Slope regional gas hydrate production modeling forecasts,” Marine and Petroleum Geology, Vol. 28, Iss. 2, Thematic Set on Scientific results of the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope, Pages 460-477, ISSN 0264-8172, doi: 10.1016/j.marpetgeo.2010.03.007.
Boswell, R., T. Collett, B. Anderson, and C. Ruppel, 2010. “Relative gas volumes for free gas and gas hydrate accumulations.” U.S. DOE-NETL Fire in the Ice Newsletter, Summer 2010. pp. 9-11.
Anderson, B., 2010. “Models of gas hydrates from the cage to the reservoir: insights from modeling at many scales,” Gordon Research Conference on Natural Gas Hydrate Systems, Colby College, Waterville, ME, June 6-11, 2010.
Anderson, B.J., “The Role of Molecular Level Modeling in Gas Hydrate Studies,” Centre Europée de Calcul Atomique et Moléculaire/Atlantic Centre for Atomistic Modelling, Dublin, Ireland, May 6-8, 2010.
Anderson, B.J., “Hydrate Reservoir Simulator Code Comparison Project: 7 problems from simple 1-D to complex 2-D simulations,” WV Regional Society of Petroleum Engineers Meeting, Morgantown, WV, April 21, 2010.
Anderson, B.J., “Multiscale Modeling: Molecular, Thermodynamic, Reservoir, and Economic Modeling of Energy Systems,” West Virginia Academy of Science 85th Annual Meeting, Morgantown, WV , April 10, 2010.
Anderson, B.J., “The Role of Molecular Level Modeling in Gas Hydrate Studies,” AIChE Annual Meeting, Nashville, TN, November, 2009.
Gaddipati, M., Anderson, B.J., 2010. “Methane production from complex gas hydrate reservoirs: Effects of reservoir heterogeneity on gas production,” West Virginia Academy of Science 85th Annual Meeting, Morgantown, WV , April 10, 2010.
Garapati, N., Anderson, B.J., “Predictions of Phase Equilibrium Data of Mixed Hydrates Using the Cell Potential Method,” West Virginia Academy of Science 85th Annual Meeting, Morgantown, WV, April 10, 2010.
Garapati, N., Anderson, B.J., “Predictions of Mixed Hydrate Phase Equilibria and the Swapping of CH4 Hydrate with CO2 and CO2+N2 Mixtures,” AIChE Annual Meeting, Nashville, TN, November, 2009.
Myshakin, E. M., Anderson, B. J., Rose, K., Boswell, R., 2010. "Simulation of long-term depressurization-induced gas production from C & D unit reservoirs, Mount Elbert-01, Milne Point Unit, North Slope Alaska, Hydrate Deposit," National Gas Hydrates Research and Development Program Review, Georgia Institute of Technology, Atlanta, GA, January, 2010.
Myshakin, E. M., Gamwo, I. K., Warzinski, R. R., 2009. “Experimental Design Applied to Simulation of Gas Productivity Performance at Reservoir and Laboratory Scales Utilizing Factorial ANOVA Methodology,” TOUGH Symposium, Berkeley, CA.
Velaga, S., Anderson, B.J., 2010. "Calculation of N2 hydrate reference parameters and cell potential parameters to analyze the N2-CO2 and N2-CH4 three-phase equilibrium and structural transitions", West Virginia Academy of Science 85th Annual Meeting, Morgantown, WV, April 10, 2010.