Hydrate Formation and Dissociation via Depressurization in Simulated and Field Samples

FEAB111

Goal
The goal of this research is to characterize natural and simulated sediment samples, and to use these sediments as hosts to form methane hydrate and to investigate the kinetics of hydrate formation and dissociation.

Performer
Oak Ridge National Laboratory – Oak Ridge, TN 37831

Background
In nature, gas hydrates are observed as either disseminated small particles of hydrate within sediments (often fine grained clays), or as massive nodules or vein-like sheets within fractures or faults. From an economic viewpoint, locating and utilizing massive hydrate deposits is key to producing methane hydrates as an energy resource. However, the bulk of gas hydrate within seafloor sediments are likely to be found as disseminated particles that would be difficult to utilize economically. Therefore, if seafloor gas hydrates are to be used as a hydrocarbon resource, it is necessary to understand how massive hydrates form in the seafloor and the geologic controls on their distribution.

In this study, methane hydrate accumulation processes and controls will be examined in the laboratory through hydrate accumulation experiments using free methane gas bubbles percolated through simulated and natural sediment systems. These experiments aim to simulate hydrate accumulation processes which may be occurring within seafloor sediments, allowing observation of hydrate accumulation and growth in the laboratory.

Potential Impact
This research project, which utilizes man-made and natural core samples to produce methane hydrates, will provide fundamental insights into where to look for potentially commercial methane hydrate accumulations, assess potential fields for production scenarios, and assess stability and safety issues.

Accomplishments
The Seafloor Process Simulator (SPS) at Oak Ridge National Laboratory is a unique experimental facility, ideally suited to the determination of kinetic, thermophysical and mechanical properties of methane hydrates that are relevant to understanding their environmental significance and their effects on the mechanical stability of the seafloor. Not only can the physical conditions be controlled, but the size and design of the vessel permit direct observation of the hydrate formation processes, and investigation of how these processes are influenced by the heterogeneities that can be expected in nature.

(A) 72-liter Seafloor Process Simulator (SPS) pressure vessel used in the experiments. The SPS has >30 access ports and windows for instrumentation and observation of experiments. The sediment column (B) was suspended within the vessel and submerged in distilled water throughout the experiments. Methane gas was introduced into the column either through the bottom endcap or a capillary placed within the sediment. In some experiments methane saturated water was also circulated through the column using an external HPLC pump and collected in a secondary reservoir within the vessel (C).

Experiments have been conducted within a transparent cylinder (60 cm length, 4.8 cm diameter) using commercially available Ottawa sand and black aquarium sand (<500 micron grain size) as well as natural sediments collected by ODP Leg 204 at Hydrate Ridge and the Hot Ice I drilling project in Alaska’s North Slope permafrost gas zone. Pressure and temperature conditions were maintained for at least 12 hours prior to experiments to allow the water of the SPS to become saturated in methane.

The results of these experiments [see Topical Report June 2007] demonstrate that in systems containing free methane gas, hydrate is likely to nucleate on the surface of methane gas bubbles, forming a film of methane hydrate. This is likely due to the supersaturation of methane at the bubble/water interface as a result of sluggish methane diffusion into surrounding water. If bubbles accumulate within the sediments within void spaces or at interfaces between sediment types, massive hydrate growth is likely to occur. Therefore, bubble accumulation points are likely to control where massive hydrate nodules and deposits will form in systems with a free gas phase.

In late 2006, the Distributed Sensing System (DSS) was delivered to ORNL and by early 2007 was incorporated into the SPS. This fiber optic based temperature/strain sensing system allows for 3D monitoring of hydrate formation and dissociation processes within large volume sediment samples.

One homogeneous and two heterogeneous sediment experiments have been conducted with the integrated SPS/DSS system. In the homogeneous sediment experiment, sieved sand was placed within a 33 liter PVC container and saturated to 30% with water. The vessel headspace was then pressurized with methane, the setup was cooled to ~1 ^oC for three days before rapid depressurization. Dissociation data was collected for two days after depressurization. The two heterogeneous sediment experiments were run using sieved sand with a 3-inch layer of silt placed directly in the center of the sediment column and utilized a gas injection system that allowed methane injection at a very slow rate (3-5 mL/min) from the base of the 100% water-saturated sediment column, thus more closely simulating a natural system where gas percolates up through the hydrate stability zone from below. These experiments have generated an overwhelming amount of data which is currently being analyzed.

Temperature and pressure data collected from experiment using natural sediments from Hydrate Ridge. Time zero represents the point of initial pressurization with methane gas through the sediment column. The temperature increase during pressurization is due to hydrate formation, an exothermic process. The plateau in temperature data and change in slope in the pressure data at approximately 12 hours after pressurization are due to hydrate dissociation, an endothermic reaction.

ORNL is also conducting scattering and diffraction studies focused on determining the effect of temperature and pressure on the structural properties of relevant hydrate materials. In August 2007, Mt. Elbert core samples were received from Lawrence Berkeley National Laboratory and low temperature x-ray powder diffraction data was collected. Time/temperature dependent x-ray powder diffraction studies have also been done on some of the Gulf of Mexico Green Canyon samples supplied by Texas A&M. The phase fractions (wt% ice vs sII hydrate) and lattice parameters for both ice and sII hydrate have been plotted as a function of temperature and time for decomposition information. The results will be presented by C.J. Rawn at the 2008 International Conference on Gas Hydrates in Vancouver, Canada.

Current Status
Large volume hydrate-sediment characterization experiments will continue to be conducted to assess the effects of sediment heterogeneity and methane flux pathways on hydrate accumulation processes. Large void spaces, sand lenses, and fine grain material will be assembled within the SPS to create model sediment columns. The rate and distribution of hydrate accumulation will be monitored using the new DSS to make time-resolved 3D temperature and strain measurements on the cm scale within large sediment volumes in the SPS. These experiments will also allow for cm-scale monitoring of dissociation kinetics, sediment movement, and flow paths, as well as assessment of possible ice formation as a result of production. These experiments will provide a better understanding of the distribution of hydrate within heterogeneous sediment systems and contribute to the development of efficient production practices.

Using the DSS and a circulating warm water source studies will also be conducted to improve the understanding of the relationship of overheating and depressurization on gas production. Production scenario variables such as hydrate formation, stability, water icing, and gas evolution (production) rates from massive hydrates will be assessed. The quantitative phase analysis of ice vs. hydrate will be determined using in situ neutron and/or X-ray diffraction.

Neutron and X-ray scattering will be used to determine the thermal expansion and/or bulk modulus of relevant hydrate compounds. Time resolved neutron and X-ray diffraction studies will be used to measure hydrate lattice parameters as a function of temperature and pressure. Additional work may also include time resolved neutron scattering studies of hydrate nucleation and dissociation to observe phase transitions and measure reaction kinetics in situ.

Project Start: July 1, 2002
Project End: September 30, 2009

Project Cost Information:
All DOE Funding
FY04 - DOE Share - $125,000
FY05 - DOE Share - $200,000
FY06 - DOE Share - $300,000
FY07 - DOE Share - $250,000
FY08 - DOE Share - $186,000
Total Funding to Date - $1,061,000

Contact Information:
NETL – John Terneus (John.Terneus@netl.doe.gov or 304-285-4254)
ORNL – Tommy Joe Phelps (phelpstj@ornl.gov or 865-574-7290)

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].

Fire in the Ice article [PDF-972KB] "Oak Ridge Facilities Well Suited For Both Education and Collaborative Research" By Tommy J. Phelps and Claudia J. Rawn, Oak Ridge National Laboratory - Fall 2004 edition, pg. 4

Interim Report - Hydrate Formation and Dissociation via Depressurization in Simulated and Field Samples [PDF-846KB] - June, 2006

Topical Report - Experimental Formation of Massive Hydrate Deposits From Accumulation of CH4 Gas Bubbles Within Synthetic and Natural Sediments [PDF-1.06MB] - June, 2007

Fire in the Ice article [PDF-1.01MB] "New Sensing Technology at Oak Ridge National Lab Expands Capabilities for Meso-Scale Hydrate Research" By Megan Elwood Madden, Oak Ridge National Laboratory - Winter 2007 edition, pg. 8

2008 ICGH Paper - Application of Fiber Optic Temperature and Strain Sensing Technology to Gas Hydrates [PDF] - August, 2008

2008 ICGH Paper - Low Temperature X-Ray Diffraction Studies of Natural Gas Hydrate Samples from the Gulf of Mexico [PDF] - August, 2008

2008 Hydrate Peer Review [PDF-4.76MB]

Pertinent Publications
McCallum, S.D, Riestenberg, D.E., Rawn, C.J., and Phelps, T.J.. 2005. Meoscale research of gas hydrates. Manuscript to be submitted in 04-2005.

Zatsepina, O., D. Riestenberg, S. McCallum, M. Gborigi, C. Brandt, B.A. Buffett, and T. J. Phelps. 2004. Influence of water thermal history and overpressure on CO2-hydrate nucleation and morphology. American Mineralogist. 89:1254-1259.

Rawn, C and T, J. Phelps, 2004. Oak Ridge Facilities for Studying Natural Gas Hydrates are well suited for Graduate Education and Collaborations. Fire In The Ice Newsletter article, Fall 2004.

Colwell, F. S., T. Nunoura, M. E. Delwiche, S. Boyd, R. Bolton, D. Reed, K. Takai, R. M. Lehman, K. Horikoshi, D. A. Elias, and T.J. Phelps. 2004. Significance of Methanogenic Microorganisms in Sediments Collected from the Mallik 5L-38 Gas Hydrate Research Well. Geological Survey of Canada Bulletin.

Riestenberg, D., O. R. West, S. Lee, S. McCallum, and T. J. Phelps. 2003. Sediment Surface Effects on Methane Hydrate Formation and Dissociation. Marine Geology. 198: 181-190.

Phelps, T. J., D. J. Peters, S. L. Marshall, V. Alexiades, G. K. Jacobs, J. G. Blencoe, M. T. Naney, J. L. Heck and O. R. West. 2001. A new experimental facility for investigating the formation and properties of gas hydrates under simulated seafloor conditions. Review of Scientific Instruments, 72 1514-1521.

McCallum, S.D, Riestenberg, D.E., Rawn, C.J., and Phelps, T.J.. 2005. Meoscale research of gas hydrates. Abst. Of the Annual ACS. Meeting, 2005.

Riestenberg, D., O. Zatsepina and T. J. Phelps. 2004. Gas Hydrate Nucleation Processes. American Geophysical Union Meeting, December 8-12, 2003, San Francisco, CA.

Riestenberg, D. E., T. J. Phelps, S. Y. Lee, O. R. West, and C. Tsouris, 2002. SPS investigations of the formation and stability of gas hydrates. Presented at the Methane Hydrates Interagency R&D Conference, Washington, DC, March, 2002.

West, O., Phelps, T. J. 2002. Methane and carbon dioxide hydrate investigations using a 70-L high pressure vessel. TMS 2002 Annual meeting, Seattle, WA, February, 2002.

West, O. R., D. E. Riestenberg and T. J. Phelps. 2002. Seafloor Process Simulator for laboratory examination of natural gas hydrate sediments. Naturally Ocurring Gas Hydrates Data Collection Workshop. Houston Texas, March, 2002.

Riestenberg, D. E., O. R. West, L. Liang, and T. J. Phelps. 2000. Effects of particle size and mineralogy on methane hydrate nucleation and dissociation pressures. Abst. Am. Geophys. Union. Fall Meeting, San Francisco, CA, December, 2000.

Role for biogeoscienes in subsurface research: VaTech, 10-2004

Deep Underground Science and Engineering Program: Biogeosciences. DUSEL, Berkeley, CA. 8-2004

Biogeochemistry of deep subsurface environments. NSF-NRF-REU, UVOS, South Africa. 7-2004

Life and times of deep subsurface microorganisms. Western Carolina University. 12-2003.

Subsurface biogeochemical processes and potential applications for the 21st century. Miss. S.U., Starksville, MS. 10-2003.

Examining highly diverse sedimentary deposits of the deep biosphere. Intern.l Limnology Conference, Flagstaff, AZ . 3-2003

Studies of natural gas hydrates at in situ temperature and pressure. ODP Pressure Coring Workshop, Texas A&M, 02-2003

Biogeochemistry of Deep subsurface Environments. NESS, Washington DC, 10-2002

Life in the deep subsurface, LBNL , Berkeley, CA, 07-2002