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In recent years, researchers have also upgraded the geotechnical capabilities of the Gas Hydrates Physical Properties Laboratory.  Geotechnical measurements provide critical information about the strength, behavior, and hydraulic properties of sediments, results important for gas hydrate reservoir and geohazard studies.

Major equipment includes two load frames and cells for consolidation and triaxial testing, a standalone conventional oedometer for one-dimensional consolidation, and fall‐cone penetrometer.  Whenever possible, data acquisition and control of the geotechnical devices have been automated.

USGS scientisit using oedometer laboratory equipment
Sediment consolidation in an oedometer provides constraints on how much the reservoir sediment is likely to compact while methane from the reservoir’s gas hydrate is extracted as an energy resource.  Compaction data helps engineers optimize the construction and operation of wells that target gas hydrate reservoirs.

Research conducted by the USGS Gas Hydrates Project sometimes requires the synthesis of gas hydrate as a pure phase or within sediments.  The group works closely with the USGS Earthquake Program in Menlo Park, California, where the ice method for synthesizing pure-phase gas hydrate was pioneered. The Physical Properties Laboratory built upon that pure-phase work and began synthesizing gas hydrate from aqueous phase (dissolved) methane, a mechanism that is likely widespread in natural systems.

water circulating in a fume hood between a low temperature cylinder with high pressure methane gas
Gas hydrate can be formed in sediment in several ways, but forming hydrate from methane that has first been dissolved in water is thought to generate pore-space gas hydrate distributions that most closely mimic those in nature. Shown above, water circulates in a fume hood between a low-temperate cylinder with high-pressure methane gas in contact with water, dissolving and transporting that methane over time through the gas hydrate growth and measurement chamber, where hydrate grows in sediment and properties such as permeability can be measured.

In some experiments, the Gas Hydrates Physical Properties Laboratory uses benchtop transparent micromodels (microfluidic pore models). Micromodels are etched from non-reactive materials (e.g., glass) to have specific two- or three-dimensional morphologies that mimic sediment pores and throats. USGS Gas Hydrates Project researchers have particularly focused on how fine-grained sediments (“fines”) migrating with fluids could clog porous media. These studies have particular significance for analyzing the migration of gas and fluids to a wellbore during production testing of gas hydrate reservoirs.  The group works closely with the USGS Earthquake Program in Menlo Park, California, where expertise in scanning Electron Microscopy (SEM) allows visualization of even the fine-grained sediment particles in support of how we interpret other measurement results, such as from consolidation or flow-clogging tests.

4 images depicting glass micromodel,  fluid flow through solid cylinders, electron microscope images,
A glass micromodel (upper left) allows fluid flow through gaps between solid cylinders (gap size of 100 micrometers is shown in the upper-right image). Injecting fine-grained materials allows us to characterize the conditions in which clogs occur, as they have done in the upper- and lower-right pictures. Scanning electron microscope images (lower left) of the fine-grain sediment often reveals which sediment components are contributing to clogs and other physical property results.  In the case described in the images here, sediment from the Ulleung Basin Gas Hydrate 2 Project (UBGH2) was rich in diatoms (shown in the lower images), which are prone to clogging due to their shapes and relatively large sizes of complete and fractured diatoms. (Credit William Waite (upper left), Laura Stern (lower left) and Jang et al., 2020 (right-hand images)   

To support research on methane bubbles emitted from the seafloor as gas migrates through sediments or as gas hydrate degrades, the Physical Properties Laboratory also manages a counterflow device capable of isolating and holding stationary a single gas bubble or a gas bubble coated in hydrate.  For the hydrate former, the instrument uses the noble gas xenon, which forms hydrate at close to ambient pressures and temperatures. The counterflow device is used to estimate the rates of formation and dissolution of hydrate shells around gas bubbles and to measure the rise velocity and acoustic properties of hydrate-coated gas bubbles.

counterflow device capable of isolating and holding a single gas bubble
By circulating water downward through a clear chamber (“capture cone”), bubbles of gas can be held, imaged and studied over time.  The left image shows bubbles of xenon in the process of developing coatings of gas hydrate.  The shiny bubble indicated near the top is hydrate-free, the white/opaque bubbles have coatings of xenon hydrate.  A few bubbles are in transition, with shiny, hydrate-free tops and white, hydrate-coated bases.

 

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