Goal
The primary goals of this research are to: 1) provide hydrate-relevant, experimentally measured key physical parameters, including thermal, hydrological and geomechanical properties, as input for numerical simulations and, 2) investigate alternative methods and scenarios for gas production to improve production efficiency and mitigate potential hazards.

Performers
Yongkoo Seol ? NETL Office of Research & Development
Eilis Rosenbaum ? NETL Office of Research & Development
Jeong Choi ? Oak Ridge Institute for Science and Education
Jongho Cha- Oak Ridge Institute for Science and Education

Location
National Energy Technology Laboratory - Morgantown, West Virginia

Description
Research will be lab-based and will focus on establishing key physical parameters for hydrate and/or hydrate bearing sediments and the investigation of hydrate system behaviors in response to production-relevant stimuli.

Specific activities will be focused around the following four areas:

1) Thermal property measurements under in-situ conditions
Thermal conductivity and diffusivity data will be measured under in situ (hydrate ?relevant) pressures and temperatures using laboratory synthesized cores that contain varied hydrate saturations. An NETL developed thermal conductivity sensor that minimizes sample disturbance will be used to measure thermal properties in synthesized cores that contain varied hydrate saturations. Existing equipment, facilities and pressure vessels at NETL will be used for measurements of laboratory prepared samples.

  
Pressure vessel with installed NETL-developed thermal conductivity sensor

2) Geomechanical strength, deformability and seismic properties of hydrate bearing sediments and numerical analysis
Laboratory experiments will be conducted to assess the impacts of hydrate formation and dissociation on the mechanical property and stability of unconsolidated sediments, and to provide information for the enhancement / development of computation models on mechanical stability of hydrate bearing sediments that are subjected to gas production. An initial assessment of current constraints on geomechanical (mechanical stiffness, shear strength, and time-dependent behavior), geophysical (seismic velocity and attenuation) and index properties (porosity, permeability, gas saturation/distribution, and hydrate saturation/distribution) will be performed to determine which are the most critical for the planned numerical simulation activities. From that assessment, an experimental plan to acquire the needed data using laboratory synthesized samples will be developed for different hydrate formation modes and for lithologies representative of sealing formations. On the basis of the property data obtained, a constitutive model will be developed to describe the experimentally-observed stress-strain behavior as a function of index properties. All the experimental data and their relationships will be incorporated into the THM model code (FEHM) to simulate the impact of large-scale gas production from hydrate reservoirs on geomechanical stability of hydrate-bearing sediments and seal formation.

Graphical representation of geomechanical and acoustic property test pressure vessel

3) Experimental characterization of CO₂-CH₄ hydrate conversion
Field test results from the recently completed ConocoPhillips hydrate gas exchange test are expected to identify needs in experimental validation and support to improve the interpretation and understanding of the complicated field data. Laboratory experimental support will be provided through this effort and is expected to include: a feasibility study of injecting CO₂ to replace CH₄ in natural reservoirs; and kinetic measurements of the exchange processes. The experiments will examine (1) the effect of the presence of free water and mixed gases on the CO₂ or mixed gas hydrate formation and (2) kinetic mechanisms of the formation of CO₂ ?CH₄ hydrate conversion and CH₄ hydrate reformation during exchange within the deep CH₄ hydrate stability zone. Multiple experiments will consider the different materials for porous media, various composition of injection gases (e.g., CH₄, CO₂, N₂), and heterogeneity in permeability and grain sizes to explore impacts of these conditions on CO₂-CH₄ exchange efficiency.

  
Optical observations of gas hydrate formation

4) Methane production from laboratory-formed hydrate bearing sands simulating in situ gas production conditions
Laboratory core-scale gas production tests will be conducted that mimic in situ (hydrate-relevant) conditions for gas production using medical and industrial CT scanners for experimental visualization. Tests will achieve in situ gas production conditions through the use of water-backed constant pressure boundary conditions and predetermined difference in pressure between two boundary conditions which will represent a depressurization-based production approach. Most experimental simulations of gas production to date have been conducted under closed boundary conditions on one end with pressure differential. Wave speed measurements taken during hydrate formation and dissociation will be analyzed and integrated with tomographic images to investigate modeling issues regarding hydrate morphology and heterogeneity.

Additionally core-scale CO₂ formation and CO₂-CH₄ exchange experiments will be also performed. Mixed gas injection (CO₂-N₂) will also be performed to compare the impact on the efficiency of CH₄ production. The experimental activities will be performed in conjunction with numerical simulations in an effort to crosscheck and validate the mixed HRS code.

Impact
Thermal and geomechanical properties are currently predominantly measured or estimated using non-hydrate bearing sediment properties. Properties obtained using actual hydrate-bearing sediments will provide important input into hydrate property databases and contribute to improvement of reservoir-scale production modeling predictions of system behavior.

Facilities
The gas hydrate laboratory located in Morgantown is equipped with a gas hydrate experiment station with which gas hydrate can be formed and dissociated under various conditions relevant to hydrate phase stability. The laboratory is situated in proximity to the X-ray CT scanner facility in Morgantown. Various types of (CT scannable) pressure vessels can be connected to the experimental station.

Medical CT scanner running with a pressure vessel equipped with temperature and pressure control

Accomplishments

• NETL developed thermal conductivity sensors have been installed on aluminum pressure vessels where methane hydrate will be formed and thermal conductivity will be measured.
• An x-ray transparent tri-axial pressure vessel, with additional acoustic and displacement testing capability, has been completed that will allow real time visualization during acoustic and geomechanical test s.
• A reaction vessel with a viewing cell has been developed for optical observation and Raman spectra analysis.

Current Status
A literature review on thermal, geomechanical and index l properties is in progress to determine which parameters are least-well constrained and most critical for the planned numerical simulation activities. Various experimental setups, including those necessary for gas exchange tests, thermal conductivity test, geomechanics test, and gas production test, are in final fabrication stage. Each test will be linked with a CT scanner with required resolutions depending on specific needs of each test. Additionally, a Raman spectrometer will be installed on the reaction vessel (optical observation) to identify gas consumption and generation during gas exchange tests.

Project Schedule
Activities initiated in October 2012

Cost Information
DOE Contribution: FY12: ~$270,000

Contact Information:
NETL ? ORD: Yongkoo Seol (Yongkoo.Seol@netl.doe.gov or 304-285-2029)

Additional Information
In addition to the information provided above, a listing of any available project related publications and presentations, as well as a listing of funded students, will be included in the Methane Hydrate Program Bibliography