Mystery solved: How gas bubbles form large methane hydrate deposits

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New research findings from the University of Texas at Austin have unravelled an important mystery about natural gas hydrate formations, advancing scientists’ understanding of how gas hydrates could contribute to climate change and energy security.

The research used a computer model of gas bubbles flowing through hydrate deposits, a widespread phenomenon that is unlikely to be possible under existing models due to the physics involved. The new model helps explain how some deposits grow into massive gas hydrate deposits, such as those found under the Gulf of Mexico.

A paper describing the research was published in the journal Geophysical Research Letters on 16 February 2020.

Gas hydrates are an icy substance in which gas molecules, typically methane, are trapped in water ice cages under high pressure and low temperature. They are abundant in nature, host a significant amount of the world’s organic carbon and could become a future energy resource. However, many questions remain unanswered as to how hydrate deposits are created and develop.

One of these questions has been raised by field observations that have discovered methane flowing freely as a gas through underground hydrate deposits. What puzzled the scientists is that under the conditions in which hydrates occur, methane should only exist as hydrate, not as a free gas. To solve the mystery of the free flowing gas, a team of geoscientists led by Dylan Meyer, a PhD student at UT Jackson School of Geosciences, recreated in the laboratory what they had seen in the field.

Using this data, they hypothesized that the hydrate that forms in a deposit also acts as a barrier between gas and water, limiting the rate at which new hydrate is formed and allowing much of the gas to bubble through the deposit. They developed this idea into a computer model and found that the model corresponded to the experimental results. After scaling, they also agreed with evidence from field studies, making it the first model of the phenomena to successfully perform both. Importantly, the model suggests that gas flowing through the subsurface can accumulate in large, concentrated hydrate reservoirs, which could be suitable targets for future energy sources.

“The model convincingly reproduces a series of independent experimental results that strongly support the basic concepts behind it,” said Meyer. “We believe that this model will be an essential tool for future studies investigating the development of large, highly concentrated hydrate reservoirs that experience relatively rapid gas flow through porous media.

The study is the first time that this type of model has been created using data from experiments designed to mimic the gas flow process. The team produced its own hydrate deposit in the laboratory using a mixture of sand, water and gas, and recreated the extreme conditions found in nature. Their efforts provided them with realistic and relevant data from which to develop their model.

Co-author Peter Flemings, a professor at the Jackson School, said that understanding how methane gas moves through hydrate layers underground is important for understanding the role of methane in the carbon cycle and its potential contribution to global warming.

“The paper provides an elegant and simple model to explain some very challenging experiments,” Flemings said.

The study’s experiments were conducted in specialized laboratories at the Jackson School, but the model was the result of cross-campus collaboration between two UT schools, the Jackson School and the Cockrell School of Engineering.

Meyer, Flemings and Kehua You, a researcher at the University of Texas Institute of Geophysics (UTIG), had developed the original computer code to explain their experimental results, but it was only in collaboration with David DiCarlo, an associate professor at the UT Cockrell School of Engineering, who showed them how to use analytical mathematics to represent the results, that they were able to successfully tackle the problem in a way that was similar to what they saw in nature.

The work is the culmination of Meyer’s research and builds on two previously published papers that focused on the results of his laboratory experiments. Meyer graduated from the Jackson School with a PhD in 2018 and is now a postdoctoral fellow at Academia Sinica in Taipei.

The research was funded by the US Department of Energy (DOE) and is part of a broader partnership between the DOE and the University of Texas at Austin to study methane hydrate deposits in the Gulf of Mexico.

Many of the laboratory experiments included in the current study were conducted by Meyer at the UT Pressure Core Center, a laboratory at the Jackson School that was established to store and study pressure cores from natural methane hydrate deposits in 2017 and remains the only facility of its kind at the university.

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I am The Washington Newsday correspondent. I cover general science and Nasa news. I have been in the Science Desk's Technology Beat since joining Washington Newsday in 2018. You can contact me at [email protected]

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