Proven under Pressure: USGS Advances Capabilities for High-Pressure Seafloor Samples Containing Gas Hydrate

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Meet USGS' newest laboratory!

In 2015, a drilling expedition staffed by scientists from India, Japan, and the United States discovered widespread, high-saturation accumulations of natural gas hydrate in the sediments of the Bay of Bengal during the second Indian National Gas Hydrate Program (NGHP-02).  This expedition marked the first discovery of Indian Ocean methane hydrate deposits that might contain producible amounts of natural gas.  Another highlight of the expedition was the unprecedented recovery of over 500 feet of sediments in pressure cores, which are specially designed to maintain sediments and their associated gas hydrates at the original sub-seafloor pressure conditions.

Image shows two scientists moving a sample of the gas hydrate
A pressure core containing hydrate-bearing sediments recovered from beneath the seafloor during the NGHP-02 drilling expedition in the Indian Ocean in 2015 is delivered by Mike Mimitz (Geotek Ltd., blue coveralls) to the Woods Hole Coastal and Marine Science Center in March 2017 after the core’s 10,000 mile sea voyage from Japan. (Image courtesy of Geotek Ltd.)

After about 18 months in storage at the National Institute for Advanced Industrial Science and Technology (AIST) in Sapporo, Japan, five of the pressure cores were delivered to the USGS Woods Hole Coastal and Marine Science Center in March 2017.  The pressure cores will be analyzed in the newly-inaugurated USGS Hydrate Pressure Core Analysis Laboratory (HyPrCAL).  This facility is the first in the U.S. to be designed for and dedicated to the analysis of pressure cores.  USGS scientists will use HyPrCAL to conduct geotechnical, electrical, and hydraulic measurements on hydrate-bearing pressure cores and to complete benchtop testing of methane production from gas hydrates.

Gas hydrate is a naturally-occurring, ice-like substance that concentrates methane gas within cages of water molecules.  Globally, gas hydrate traps vast amounts of methane and is stable only within the range of pressure and temperature conditions found in some sea floor sediments and permafrost environments.  The large amounts of methane in the deposits and their occurrence at shallower depths than conventional gas reservoirs render gas hydrates a potential energy resource.  

Image shows several silver cylinders sitting on a building floor
Pressure core transport and storage chambers awaiting certification for shipping within the U.S.  When completed, these chambers will include pressure and temperature monitoring and an accumulator to stabilize the chamber’s pressure. (Image courtesy of Spencer Composites Corporation)

Because gas hydrate is only stable at certain pressures and temperatures, collecting and storing samples for analysis in the laboratory have been challenging. The ability to retrieve samples and analyze them in a laboratory setting has been among the most important innovations of the past 15 years for advancing understanding of the energy resource potential of gas hydrate. 

“This is an exciting time to be working on gas hydrates,” said Carolyn Ruppel, Chief Scientist for the USGS Gas Hydrates Project.  “With support from the Department of Energy, the USGS has been able to build on our existing expertise in pressure core analysis and establish the appropriate facilities and infrastructure to ensure our continued contributions to understanding gas hydrate as a potential energy resource.”

The pressure cores retrieved during the Indian Ocean expedition were delivered to the USGS using a special packing method devised by Geotek, Ltd. to meet U.S. Department of Transportation requirements.  All five cores arrived at the USGS at full pressure, meaning that the hydrate recovered in these cores 21 months ago should still be intact.  USGS researchers participated in the recovery of these pressure cores aboard the D/V Chikyu in summer 2015 under the leadership of USGS Senior Scientist Timothy Collett.  Since then, USGS scientists have collaborated with their counterparts from India and AIST to develop an analytical strategy for these rare samples.

Larger image shows a USGS scientist standing in the lab, while the inset shows the outside of the lab
USGS physical scientist Lee-Gray Boze and research engineer Junbong Jang depressurize one of the test chambers that make up the Pressure Core Characterization Tools in HyPrCAL, the new USGS pressure core analysis facility.  Inset photograph shows the new laboratory in Woods Hole, Massachusetts. Credit: USGS.

The USGS HyPrCAL facility will not only analyze NGHP-02 pressure cores, but may also receive pressure cores from an upcoming U.S.-led drilling expedition in the northern Gulf of Mexico, as well as from possible future programs on the Alaskan North Slope and in international locations. 

The standalone HyPrCAL facility is refrigerated to maintain gas hydrate within its stability zone, while the pressure core chambers and the special analytical tools sustain the required pressures during analyses.  HyPrCAL hosts the Pressure Core Characterization Tools (PCCTs) originated by J. Carlos Santamarina at Georgia Tech and transferred to the USGS in 2015.  The USGS Gas Hydrates Project is modifying the PCCTs and building new devices to enhance analytical capabilities for hydrate-bearing pressure cores. 

The laboratory tools yield crucial data that help to explain measurements made in seafloor boreholes and inferences drawn from marine seismic surveys.  The PCCTs also provide the best approach for monitoring changes in sediment properties inside the pressure chambers during controlled experiments to extract methane from the gas hydrate.  The resulting data are critical for refining reservoir models for natural gas hydrate systems.

Image shows two views of the gas hydrates in the storage container
(Top) X-ray image of hydrate-bearing pressure core collected ~168 feet below the seafloor in the Indian Ocean during the first National Gas Hydrate Program (NGHP-01).  White features are hydrate, and darker material is the surrounding sediment.  Image courtesy of Geotek, Ltd.  (Bottom) Gas hydrate (ice-like material) and sediment (dark material) in a conventional core recovered from below the sea floor during NGHP-01. Photograph by T. Collett.

As part of the USGS effort to facilitate research on pressure cores in the broader community, the USGS Gas Hydrates Project is also nearing the end of an 18-month-long process to build pressure core storage chambers that meet the requirements of the American Society of Mechanical Engineers for high-pressure vessels and those of the US Department of Transportation and the American Bureau of Shipping for overland and shipboard transport to and within the US.  Once the approvals are complete, any user will be able to order chambers of the same design under the certifications being obtained now. 

Murray Hitzman, USGS Associate Director for Energy and Minerals, said, “Through these innovations and other activities, the USGS plays a leadership role in advancing national interests related to the characterization of unconventional natural gas resources trapped in methane hydrate.  These activities are an important step along the trajectory towards possible production of methane from these widespread deposits in the future.”

Completion of the HyPrCAL facility, modifications to the PCCTs, shipment of the NGHP-02 pressure cores, and construction and certification of the new pressure core storage and shipping chambers have been funded in part through an interagency agreement between the USGS and the Department of Energy’s Methane Hydrates Research and Development. 

The USGS Gas Hydrates Project is a leading international gas hydrates research program focused on energy resource, environmental, and geohazard issues. 

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