The USGS Gas Hydrates Project: Methane Ice as Energy and Climate Risk

From a U.S. Geological Survey fact sheet, January 2018.

The USGS Gas Hydrates Project studies methane hydrates in nature: how they form and where they occur, their potential as an energy resource, and how they interact with the environment. It is a joint effort of the USGS Energy Resources and Coastal and Marine Geology Programs, working with other federal agencies, some State governments, research organisations and international partners.

The project runs field programmes and joins drilling expeditions to study hydrates at sea and on land. Its scientists collect new geophysical data, sample sediments, seawater and air where hydrates occur, analyse data from partners, and run specialised laboratories.

White chunks of gas hydrate — methane ice — mixed with grey sediment, recovered by the USGS in 2010 from a few feet below the Arctic Ocean floor, in water about 8,000 feet deep. USGS.

What gas hydrate is

Gas hydrate forms when water and gas combine at fairly high pressure and low temperature into an ice-like solid. The most common gas in natural hydrate is methane — one carbon and four hydrogen atoms — which is also the main component of natural gas. The methane usually comes from microorganisms breaking down carbon-rich organic material buried in sediments; methane rising from conventional gas reservoirs can also be trapped.

The right pressure and temperature exist mostly:

• offshore, in the sediments of continental margins;
• onshore, in and beneath continuous permafrost (permanently frozen ground).

As hydrate forms, it can concentrate methane up to 180 times compared with the same gas at surface temperature and pressure. That makes it a concentrated, shallowly buried form of natural gas — one that could be an energy resource, or could be disturbed by changing ocean or atmospheric conditions.

How much is there?

Estimates of the mobile carbon trapped in gas hydrates vary tenfold. Globally, hydrates are estimated to hold 106,000–876,000 trillion cubic feet of methane. For comparison, the United States used more than 27.49 trillion cubic feet of natural gas in 2016. Studies suggest hydrates may keep at least 10–15 percent of the world's carbon out of circulation between the ocean and the atmosphere.

Hydrates are hard to study, which is why they are not better understood: they often fill only a small part of the space between sediment grains, and they break down quickly once taken out of their natural pressure and temperature.

Hydrates as an energy resource

Project scientists have led, advised or taken part in more than a dozen drilling projects in deep-water and Arctic permafrost settings: on Alaska's North Slope, in Canada's Mackenzie Delta and the northern Gulf of Mexico, and off India, South Korea and the northern Cascadia margin. This work has greatly advanced understanding of what controls where hydrates occur and whether gas can be extracted from them.

The drilling rig used in 2007 to explore gas hydrates in onshore permafrost near Prudhoe Bay, Alaska. USGS.

• Finding deposits: the USGS treats hydrates as petroleum systems to evaluate basins that may hold concentrated deposits, often using existing seismic and borehole data to infer where hydrate is concentrated.
• Test wells: with the Department of Energy, other agencies, international partners and industry, it plans research wells to recover hydrate samples and test gas production, which helps show whether hydrates could be an economic source of gas.
• Assessment: in 2008 the USGS completed the first-ever assessment of methane recoverable from gas hydrates with existing technology, for permafrost hydrates on Alaska's North Slope, using a method that can be applied elsewhere.

USGS scientists measuring sediment cores from a drilling expedition studying the energy potential of gas hydrates. USGS.

Hydrates and the environment

Warmer ocean or air temperatures may destabilise hydrate deposits, releasing methane into the surrounding sediments and possibly the ocean or atmosphere. Methane is a potent greenhouse gas, so methane reaching the air could add to warming. In the ocean, though, most methane released at the sea floor dissolves in the water, and bacteria turn some of it into carbon dioxide; very little reaches the air if released deeper than several hundred feet.

Hydrate is most likely to break down as oceans warm in two settings:

Gas hydrate under a mussel-encrusted cap of rock on the floor of the northern Gulf of Mexico, imaged by a remotely operated vehicle run by NOAA's Office of Ocean Exploration and Research.

The USGS has:

• mapped where subsea permafrost lies, which largely decides where vulnerable hydrate persists beneath the U.S. Arctic shelf;
• run Arctic expeditions to map hydrates under the upper continental slope, measure methane release to the atmosphere at high latitudes, and measure how fast bacteria consume methane in seawater;
• helped discover hundreds of previously unknown methane seeps on the U.S. Atlantic margin from 2012 to 2014, and, with the Department of Energy, NOAA and others, continues cruises there to map hydrates, find methane plumes and sample the sea floor;
• worked with the British Geological Survey to link the timing of methane releases to past climate events.

Sea-floor stability

Hydrate formation and gas migration are unlikely to cause submarine landslides directly, but hydrates or gas bubbles in sediment may leave slopes primed to fail in an earthquake. USGS researchers were among the first to notice that hydrates and submarine slides occur together; such slides can cause tsunamis and damage pipelines and other sea-floor infrastructure. USGS surveys have produced dramatic images of slide scars on U.S. margins and of the gas and hydrate beneath them.

In the lab, the project measures how hydrate-bearing and gas-charged sediments behave under stress, for models of slope failure, and studies how sediment volume changes as hydrate breaks down — important for understanding subsidence around wells drilled through hydrate, including future wells to produce methane from it.

Laboratories

• A low-temperature scanning electron microscope shows individual hydrate crystals and sediment grains.
• A pressure laboratory measures hydrate-bearing samples kept at their original pressure from recovery through storage and analysis; with bench tests of methane production, this helps gauge reservoir properties and energy potential.
• Geochemical tools measure organic carbon in seawater and sediment and continuously track methane and carbon dioxide in surface waters and the air during ship surveys.

Gas hydrate crystals in a sediment sample under a scanning electron microscope; the scale bar is 50 micrometres, about 0.002 inches. USGS.

Sources

• U.S. Geological Survey, The U.S. Geological Survey's Gas Hydrates Project, Fact Sheet 2017–3079, January 2018. https://doi.org/10.3133/fs20173079 — text order and figures recovered from the PDF; the imported page had interleaved its two columns.
• The fact sheet's image of a methane seep off Virginia, taken by a remotely operated vehicle run by Oceaneering, Inc., is not reproduced.
• Rewritten in hubnx's own words.