New technique to extract methane from marine sediments

Researchers from the Indian Institute of Technology in Madras have developed a new, energy-efficient technique to extract methane gas trapped in gas hydrates – ice-like cages present in shallow marine sediments¹.

The researchers say this technique will enable the indigenous supply of natural gas, reducing India’s natural gas import burden.

Natural gas hydrates are crystalline-ice-like compounds that are formed when water makes a cage-like structure around small methane molecules. Such a cage-like structure forms when water and methane molecules come into contact at low-temperature and high-pressure conditions in clayey and sandy marine sediments.

Off India’s shores, where the country could legally tap non-living and living marine resources, gas hydrates contain almost 1,900 trillion cubic meters of methane gas. This is 1,500 times the country's current gas reserve.

To devise a way to tap such a vast reserve of natural resource, the researchers, led by Jitendra Sangwai, tested the efficacy of several methods, including the combination of thermal stimulation and depressurisation. They then explored the efficacy of the combined method in extracting methane by applying it on a simulated marine clayey hydrate reservoir in the presence of seawater. In depressurisation, a gradual decrease in pressure released gas from the hydrate reservoir.

They found that the combination of the two processes is more efficient for methane production from clayey hydrate reservoir than when they are used alone.

“Besides meeting the enormous demand for energy all over the world, methane extraction from gas hydrates can also reduce the release of this greenhouse gas into the environment,” adds Sangwai.

Amiya Jana, an expert on gas hydrates from the Indian Institute of Technology in Kharagpur, is skeptical about the new methane extraction technique.

“During mass production, natural gas leakage to the atmosphere may have a devastating effect, since methane is much more damaging than carbon dioxide,” says Jana, who was not involved in this research. Methane escaping from hydrates may even damage marine ecosystems, he warns.

However, Sangwai and colleagues seem optimistic. “The depressurisation method can be easily manageable since the rate of gas release is controllable,” says lead author Vishnu Chandrasekharan Nair, adding that “besides a clayey hydrate, this method is also suitable for any hydrate reservoir”.

References

1. Nair, V. C. et al. Natural gas production from a marine clayey hydrate reservoir formed in seawater using depressurization at constant pressure, depressurization by constant rate gas release, thermal stimulation, and their implications for real field applications. Energy Fuels 33, 3108-3122 (2019)