|NETL-ORD – Experimental Analysis and Characterization of Hydrate-Bearing Sediments to Support Numerical Reservoir Simulations
||Last Reviewed 7/15/2013
The primary goals of this research are to (1) provide hydrate-relevant, experimentally measured key physical parameters—including thermal, hydrological, and geomechanical properties—as inputs to numerical simulations and (2) investigate alternative methods and scenarios for gas production to improve production efficiency and mitigate potential hazards.
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
National Energy Technology Laboratory - Morgantown, West Virginia
Research will be lab-based and focused on establishing key physical parameters for hydrate and/or hydrate-bearing sediments and investigating hydrate system behaviors in response to production-relevant stimuli. Specific activities will be focused on the following four areas:
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 of various hydrate saturations. An NETL developed thermal conductivity sensor that minimizes sample disturbance will be used to measure thermal properties in synthesized cores of various hydrate saturations. Existing NETL equipment, facilities, and pressure vessels will be used to measure 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 are being conducted to assess the impacts of hydrate formation and dissociation on the mechanical properties and stability of unconsolidated sediments and to provide information for the enhancement/ development of computational models of the mechanical stability of hydrate-bearing sediments that are subjected to gas production. An initial assessment of current constraints on geomechanical (mechanical stiffness and shear strength) geophysical (seismic velocity and attenuation) and index properties (porosity, permeability, gas saturation/distribution, and hydrate saturation/distribution) is in progress to determine which of these are most critical for the planned numerical simulation activities. On the basis of the property data obtained, a plasticity-based constitutive model is being developed to describe the experimentally-observed stress-strain behavior as a function of methane hydrate saturation All the experimental data and their relationships will be incorporated into a selected Thermal-Hydrological-Mechanical (THM) model code to simulate the impact of large-scale gas production from hydrate reservoirs on geomechanical stability of hydrate-bearing sediments and seal formation.
Experimental setup for geomechanical and acoustic property test pressure vessel mounted on the industrial CT scanner (Left), and CT scan images showing a sample under vertical compression.
Strain-stress profiles for multi-staged trained trial axial test (Left) and Mohr’ circles and failure envelop for sand sample (Right).
3) Experimental characterization of CO2-CH4 hydrate conversion
Field test results from the recently completed ConocoPhillips hydrate gas exchange test are expected to identify experimental validation and support needs that will improve interpretation and understanding of the complicated field data. Laboratory experimental support will be provided through this effort and is expected to include a study to determine the feasibility of injecting CO2 to replace CH4 in natural reservoirs and the kinetic measurements of the exchange processes. The experiments will examine (1) the effect of the presence of free water and mixed gases on CO2 or mixed gas hydrate formation, (2) kinetic mechanisms of the formation of CO2-CH4 hydrate conversion and CH4 hydrate reformation during exchange within the deep CH4 hydrate stability zone, and (3) an exchange mechanism study using Raman spectroscopy. Multiple experiments will consider the use of different materials for porous media, the composition of various 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.
Multi-vessel kinetics measurements set up with gas chromatography real time analysis (Left) and Raman spectroscopy (Right)
4) Methane production from laboratory-formed hydrate bearing sands simulating in situ gas production conditions
Laboratory core-scale gas production tests that mimic in situ (hydrate-relevant) conditions for gas production will be conducted 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 a 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.
Core-scale CO2 formation and CO2-CH4 exchange experiments will be also performed. Mixed gas injection (CO2-N2) will be performed to compare the effectiveness of individual gases on produced CH4 . The experimental activities will be performed in conjunction with numerical simulations in an effort to crosscheck and validate the mixed Hydrate Reservoir Simulation (HydrateResSim or HRS) code.
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.
The gas hydrate laboratory located in Morgantown is equipped with an experiment station within which gas hydrates 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. Various types of (CT scannable) pressure vessels can be connected to the experiment station.
Medical CT scanner (Left) and Micro CT scanner (Right) running with a pressure vessel equipped with temperature and pressure control
- NETL-developed thermal conductivity sensors have been installed on aluminum pressure vessels within which methane hydrate will be formed and thermal conductivity measured.
- Development of an X-ray transparent tri-axial pressure vessel with additional acoustic and displacement testing capability that will allow real-time visualization during acoustic and geomechanical tests has been completed.
- A reaction vessel with a viewing cell has been developed for optical observation and Raman spectra analysis.
Current Status (July 2013)
Researchers are conducting a literature review on thermal, geomechanical, and index l properties 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 and the thermal conductivity test, geomechanics test, and gas production test—are in final the fabrication stage. Each test will be linked with a CT scanner with required resolutions dependent on the 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.
Activities initiated in October 2012
DOE Contribution: FY12: ~$270,000
NETL – ORD: Yongkoo Seol (Yongkoo.Seol@netl.doe.gov or 304-285-2029)
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.