NETL-led research is offering groundbreaking insight into the mysteries of methane hydrate formation and behavior by enabling pore-scale observation in natural conditions for the first time ever. The impactful data gleaned from this research will inform future efforts to produce clean, affordable and reliable energy from these abundant natural gas resources.

Methane hydrate is a cage-like lattice of ice that forms underwater at low-temperature, high-pressure conditions, trapping molecules of methane — the chief constituent of natural gas — inside. The amount of carbon stored in gas hydrate deposits worldwide is comparable to the volume stored in all conventional fossil fuels combined, offering promising possibilities to meet global energy needs. Yet, researchers have previously only speculated as to how methane hydrates form in nature due to inadequate methods of scientific investigation.

NETL researchers, along with a collaborator from Lawrence Berkeley National Laboratory, sought to address this challenge by developing a high-resolution, X-ray computed tomography (CT) technique that provides a 3D view of hydrate-bearing sediment pores while maintaining the necessary pressure and temperature to preserve stability. Their experiments mimicked the natural conditions in which a large amount of gas leads to hydrate formation, typically under Arctic permafrost and beneath the ocean floor. Their findings are detailed in a research paper published in the June 2019 edition of the peer-reviewed journal Marine and Petroleum Geology.

Hydrate formation occurs when gas and water molecules combine in porous sediments, such as sand, under favorable conditions. Researchers focused their observation on pore habits to learn how hydrate is distributed in sediment pores and how it interacts with sediments in order to understand the potentially dynamic physical and chemical properties of hydrate-bearing sediments. Among their discoveries:

• The affinity of pore constituents to quartz sand surface follows the order of water, methane hydrate and methane gas.
• Hydrate tends to adopt round and smooth surfaces in contact with water and exhibits more angular interfaces when in contact with methane gas.
• Hydrate formation in excess-gas systems blocks or coats pores, preventing fluid flow in some cases, while hydrate formation in excess-water systems flows through pores, creating blockages only where large gas pockets exist.
• Natural brine injection can alter pore behavior.
• Evolution over time produces bigger hydrate particles that have less contact area with sand particles.
• The effects of hydrate pore habits become less important as hydrate particle size exceeds pore size.

These insights into hydrate formation and pore habits are critical for predicting the impact of possible gas production approaches. NETL’s research team is expanding its work to study the formation of high-saturation methane hydrates, which would yield greater quantities of natural gas, and investigate the potential pitfalls of thermal stimulation and depressurization methods. The ultimate goal is to identify and optimize safe, economical and effective strategies to yield high quantities of methane from gas hydrates to help meet America’s growing energy needs.

Click here to learn more about NETL’s research on gas hydrates.

Photo caption: An original CT image of methane hydrate-bearing sand is shown on the left, with a segmented and color-filled image on the right. Methane gas is represented in black.