Solving the Methane Hydrate Gas Bubble Mystery

Replacement Solving The Methane Hydrate Gas Bubble Mystery
A CORE SAMPLE CONTAINING METHANE HYDRATE (WHITE).

New research has explained an important mystery about natural gas hydrate formations and, in doing so, advanced 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 common phenomenon in nature that, according to existing models, should not be possible. The new model helps explain how some deposits grow into massive natural gas hydrate reservoirs such as those found beneath the Gulf of Mexico. A paper describing the research was published Jan. 15, 2020, in the journal Geophysical Research Letters.

Gas hydrates are an icy substance in which gas molecules, typically methane, become trapped in water-ice cages under high pressure and low temperature. They are found widely in nature, house a substantial fraction of the world’s organic carbon and could become a future energy resource. However, many questions remain about how hydrate deposits form and evolve.

One such question was raised by observations in the field that spotted methane flowing freely as a gas through hydrate deposits in the subsurface. What puzzled scientists is that under conditions where hydrates occur, methane should exist only as a hydrate, not as a free gas. To solve the mystery of the free-flowing gas, a team of researchers led by Dylan Meyer, a graduate student at the Jackson School of Geosciences, re-created in the lab what they saw in the field.

Using this data, they hypothesized that as hydrate forms in a deposit, it also acts as a barrier between gas and water, restricting the speed at which new hydrate forms and allowing much of the gas to bubble through the deposit. They developed this idea into a computer model and found that the model matched experimental results. When scaled up, they also matched evidence from field studies, making it the first model of the phenomena to successfully do both. Crucially, the model suggests that gas flowing through the subsurface can accumulate into large, concentrated hydrate reservoirs, which could be suitable targets for future energy sources.

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