The goal of this project is to develop observational and experimental data that can provide a better understanding of the basic mechanisms at work in a methane hydrate reservoir that is under production. To this end, a thorough physical understanding of underlying phenomena associated with methane hydrate production will be acquired through unique, multi-scale experiments and associated analyses. In addition, one or more mathematical models that account for the observed phenomena and provide insights that may help to optimize methane hydrate production methods will be developed.
Georgia Tech Research Corporation, Atlanta, Georgia 30332
Oak Ridge National Laboratory (ORNL), Oak Ridge, Tennessee 37831
Gas hydrates constitute an attractive and potentially large source of energy. A good assessment of methane production strategies and the subsequent design of production operations cannot be achieved without appropriate information on hydrate-sediment interaction and the changes in the physical properties of hydrate bearing sediments during hydrate formation and dissociation. There are many gaps in the understanding of gas hydrates that must be filled before technical and economically viable strategies for producing methane from gas hydrate reservoirs can be developed.
Methane hydrate production strategies will be affected by many factors. These include hydrate formation history within sediments (affects pore percolation and all forms of conduction), the hydrate itself within the pore space, subsequent gas production and recovery from porous networks, and the geomechanical evolution of the granular framework of the reservoir matrix during production. The prediction of gas recovery rates and the volume of gas produced for different reservoirs, as well as optimal development design, relies on understanding the phenomena taking place during hydrate formation and dissociation. While temperature-and pressure-controlled production approaches have been considered, all forms of energy mechanisms (including chemical and electromagnetic) and associated energy combinations within the reservoir should be explored as part of a broad search for optimal production strategies. The comprehensive physical understanding of ongoing processes must be properly captured in mathematical models that accurately describe the equilibrium and kinetic behavior of hydrates in sediments. These models can then be used to evaluate, design, and monitor/control gas production strategies. An accurate mathematical description is a key to providing an accurate assessment of the production potential of hydrate deposits and the economic viability of their development. The interpretation of physical model results and the development of analytical models must recognize scaling conditions, similarity laws, and the coexistence of multi-scale processes. Finally, the availability of proper information and reliable models will support the assessment of the environmental impact of production operations in order to prevent the implementation of unacceptable production strategies.
Experiments are being conducted at several scales, beginning with 1-D (pore and grain scale) focusing on single mineral substrates, extending to 2-D porous networks (granular layers and pore networks) in a single plane, and concluding with 3-D conditions using sediment columns. These experiments are examining formation stimulation using pressure, chemical, thermal, and electromagnetic sources alone as well as in combination. Different minerals are being used in 1-D experiments, different grain sizes in the 2-D experiments, and different grain sized/sediment mixtures in the 3-D experiments. The main advantage of the proposed multi-scale approach is the identification of fundamental processes that can be recognized as possibly governing the macroscale process of methane production from hydrates.
The data gathered, and the models developed, during this project may find application in other NETL methane hydrate projects, especially those involving computer reservoir simulations. This research will increase the understanding of the response of methane hydrates to production stimulation and the actions and reactions of released energy within the reservoir.
The study of formation and dissociation of hydrates in granular materials and porous networks has been completed. This research provided insight into emergent phenomena that do not develop in the 1-D mineral surface system, and introduced transport effects on hydrate dissociation in a controlled manner. Gas production is monitored during depressurization, heating, and CO2-CH4 replacement. Data from the 2-D experiments were used to facilitate the development of a coupled thermodynamic and transport model for hydrate dissociation in sediments .
Particle and pore-level observations made in the 1-D, 2-D, and long tube chambers have been up-scaled using discrete element methods and network models. Up-scaled data allows researchers to anticipate sediment response following dissociation, gas production efficiency and residual gas saturation, as well as the evolution of mechanical and conduction properties.
Experiments using instrumented internal cells (IICs) for specimen containment within the SPS were completed to further refine the kinetic model. This includes studies of time-dependent hydrate formation and dissociation with both wetted and non-wetted surfaces, and experiments of contact level dissociation under different driving forces.
The 1-D and 2-D chambers and various tube chambers and associated instrumentation have been designed, built and utilized since the beginning of the project. These pressure vessels were designed and fabricated to accommodate a wide range of feed-through ports and see-through sapphire end windows. Studies involved sequential tests using various pore fluids to simulate fresh to saline water, and PT histories for formation and dissociation in wetting versus non-wetting granular media. Data gathered during hydrate formation and dissociation include pressure, temperature, both mechanical and electrical impedance, and digital photography.
Additional large-scale experiments were conducted using selected sediments subjected to both effective stress and pore fluid pressure within ORNL’s SPS system and using natural sediments in the IPTC. The large volume of the SPS and its numerous ports make it ideal for well-instrumented studies of gas recovery from hydrate-bearing sediments. Test results show the convenience of instrumented internal cells (IICs) for specimen containment within the SPS, and the complexity of emergent phenomena during gas production in hydrate-bearing sediments, including gas-driven fractures and fines migration.
Results of the use of the chambers are documented in the project’s quarterly and yearly reports listed below under "Additional Information". These studies provided detailed insight into hydrate formation, hydrate contact bonding and strength, and dissociation processes.
Georgia Tech has developed and tested its new intrinsic kinetic model, which includes an experimentally-based pressure curve as an input which better reflects regulation of gas flow during the experiments. In addition, the properties of the gas are calculated using a Peng-Robinson equation of state in order to better capture the cooling effect of the chamber during gas evacuation. Simulation and experimental results for both 3-mm and 9-mm hydrate films have been completed. The new model does a better job of predicting the conditions inside the pressurized chamber within the kinetically-controlled dissociation regime for thinner hydrate film. For the thicker 9-mm film dissociation occurs at equilibrium until the film is about 3-mm thick.
Project research has been completed. The final report is available below under "Additional Information".
Phase 1 - $155,320
Phase 2 - $184,260
Phase 3 - $187,670
Phase 4 - $260,336
Planned Total Funding (if project continues through all project phases):
DOE Contribution: $787,586
Phase 1 - $49,170
Phase 2 - $63,401
Phase 3 - $60,003
Phase 4 - $71,935
Planned Total Funding (if project continues through all project phases):
Performer Contribution: $244,509
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].
Final Project Report [PDF-1.73MB] - November 2011
Special Report – Pressure-Temperature Evolution During Thermal Stimulation [PDF-241KB] - December 2007
Technology Status Assessment [PDF-212KB] - May 2007
Kick-off meeting presentation [PDF-2.43MB] - January 9, 2007