In early May 2010, the containment vessel that BP attempted to install on the leaking Macondo well in the Gulf of Mexico failed because gas-hydrate ice crystals clogged the 100-ton concrete and steel vessel. Some experts speculated early on that gas hydrates may have contaminated the cement used when installing the casing or collected into a gas bubble as well.

The incident focused attention on gas hydrates, which form when natural gas and water combine under certain pressure and temperature conditions. Gas hydrates are natural gas, primarily methane, and water frozen together. The water solidifies around the gas molecule into an ice crystal.

The crystals have long been known as a geohazard. Midstream and downstream gas producers have dealt for years with gas hydrates clogging flow lines. When cooled or pressurized, the gas hydrate’s crystal structure can cause partial or total blockages in pipelines or processing equipment, containment vessels such as used at the Macondo well, or in drilling equipment such as BOP stacks, drill strings, kill lines and chokes. Operators generally use heaters or add glycol or methanol to prevent hydrate formation.

But, gas hydrates also have another identity: that of a tremendous energy resource.

Staggering Potential

Gas hydrates are common in many parts of the world, including Arctic permafrost regions and in relatively shallow sediments in the ocean's deep waters. They are stable in these environments.

Indeed, the resource potential of methane in gas hydrate exceeds the combined worldwide reserves of conventional oil and gas reservoirs, coal, and oil shale. A May 2010 Congressional Research Service report for Congress stated that if 1% of the estimated gas hydrate resources could be developed, it would provide enough natural gas for U.S. needs for approximately 100 years.

Although research is ongoing, the Energy Information Administration (EIA) global estimates place the gas hydrate volume in ocean deposits from 30,000 trillion cubic feet (Tcf) to 49,100,000 Tcf. For the continental U.S., gas-hydrate deposit estimates range from 5,000 to 12,000,000 Tcf. Comparatively, current worldwide natural-gas resources are about 13,000 Tcf and natural gas reserves are about 5,000 Tcf.

Most of the gas-hydrate volume in the U.S. is expected to be in Federal waters, according to U.S. Geological Survey studies. Hydrates are known to exist in both onshore and offshore Alaska, offshore Washington, Oregon, California, New Jersey, North and South Carolina and in the deepwater Gulf of Mexico. In the Gulf of Mexico, gas-hydrate resources accumulate near the margins of mini-basins and at the front of the Sigsbee Escarpment.

A 2008 U.S.G.S. assessment of Alaska’s North Slope indicates that the region may hold 25- to 158 Tcf of undiscovered, technically recoverable gas-hydrate resources.

Hunting Hydrates

Today, researchers are concentrating on the identification and quantification of gas hydrate resources. Currently, seismic surveying seems to be the most direct pre-drilling means to detect and map onshore and offshore sedimentary regions for gas hydrate resources. Looking for gas hydrate sedimentation requires higher seismic shooting frequencies and shallower depths than traditional oil and gas seismic surveys. The USGS cautions that there are still uncertainties in seismic-estimation methods.

Bathymetric mapping is an indirect measurement, but it can show seafloor anomalies such as pock marks or mud diapirs where shallow gas hydrate resources may exist. However, such surface features can only show possible or past hydrate presence on the surface of the sea floor.

Once a rig is moved to a site, logging-while-drilling (LWD) equipment and core samples provide the most encouraging and accurate results. Downhole resistivity logging can show gas hydrate presence. A resistivity log that ranges between 150-175 ohmmeters can indicate a methane-hydrate interval according to a 1998 EIA report. Drilling conditions that can indicate a gas-hydrate area include unexpected loss of circulation or reservoir or wellbore collapse.

Worldwide Wrap-up

Canada: Canada’s reserves are found extensively in onshore and offshore areas in the Mackenzie Delta, Beaufort Sea Basin and in the Arctic Islands. Gas hydrates were discovered in the 1970s at Mallik Bay in Mackenzie Delta. According to the Canadian Centre for Energy, exploration in 2002 found that there are more than 200 meters of gross gas-hydrate thickness within the rock layers, containing very high concentrations of gas – up to 90% of the lattices are filled with gas. The Mallik samples are considered the best gas-hydrate cores in the world and they are now being studied globally.

China: A 2007 Chinese investigation drilled in South China Sea found sedimentary layers between 10 and 25 meters thick that were rich in gas hydrate. In the tundra of the country’s Qinghai province, a government report estimated that a gas-hydrate reserve, equal to 35 billion tons of oil equivalent, with methane concentrations as high as 99.8%, may exist in the province.

India: A 2006 study funded by the Indian government estimated that there were 1,894 trillion cubic meters in the Konkan, Krishna Godavari Basin, Mahanadi and areas around the Andaman seas, offshore India.

Japan: In 2007, the Japanese government announced that there were 1.14 trillion cubic meters of methane hydrates in a Pacific Ocean trench, the Nankai Trough, just off the eastern coast of Honshu. A government gas-hydrate program plans to complete research and development by 2018 and start commercial production. Much of Japan’s gas hydrate is about 3,200-5,000 feet below the seafloor. A Japanese company, Japan Oil, Gas and Metals National Corp. (JOGMEC), extracted gas from reserves under the tundra of northwestern Canada from about 3,300 feet.

Russia: The first gas-hydrate reserves were found below permafrost in Russia’s Siberian region in the 1960s. In 2009, Russian Mir submarines discovered new accumulations at the 1,300-foot-deep bed of freshwater Lake Baikal in southeastern part of the country near Mongolia.

South Korea: According to E&P Daily, South Korea will explore for gas hydrate reserves offshore its eastern coast in July 2010 to determine the size and potential of the resource. The evaluation areas will be in water depths of about 6,000 feet in the Ulleung Basin near the Korea Strait. The U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (NETL) reported that during the current survey 10 prospective site will be drilled. Initial estimates from 2007 claimed that as much as 600 million tons may exist, and the country wants to commercially develop the resource by 2015.

Site-specific Geohazards

Currently there are no active, commercially producing gas hydrate wells, but work to develop new technologies and modify existing technologies for this unique resource is ongoing.

Certainly, gas hydrates pose some uncommon challenges. Whether onshore or offshore, an uncontrolled gas release caused by a heated drill bit or by the rapid pressure decrease in a penetrated zone or reservoir could be a hazard.

Offshore, gas hydrate dissociation, whether from natural causes or exploration and production operations, could potentially trigger submarine landslides. The sloping continental margins contain soft sedimentation, and subsurface disruptions below the sedimentary layers can cause the softer layers to shift and sink. Gas-hydrate dissociation is thought to be the cause of the world’s largest slides, Storegga, off the east coast of Norway. It is also considered possible, though unlikely, that a sizable, uncontrolled gas release offshore could cause floating vessels to sink by turning the ocean water to foam. Another possibility is that the seafloor could erode under a jack-up rigs’ footing, or cause problems with well equipment.

Technology to create a downhole stability zone to overcome mechanical and chemical obstacles is under development and is outlined in an EIA report. Because of the thermodynamic instability associated with gas hydrates, one possible fix would be to create a stability zone beneath a pressurized zone, where pressurized gas could flow or be contained. This could cause the hydrate at the base of the zone to decompose and allow freed gas to flow towards the well bore.

A thermal stimulation method is being researched that would use hot water, steam or other heated liquid. The heated fluid could be injected into to the hydrate stability zone which would raise the zone temperature and the hydrate would begin to decompose and the freed gas would move toward the well bore. Additionally, a chemical stimulation method would use a liquid-inhibiting chemical such as glycol.

Larger-scale Risks

On a broader scale, studies of the effects on the global carbon cycle by large-scale production of gas hydrates are not well understood at this time. According to Rice University researchers, the large amount of carbon stored in gas hydrates is likely 10 to 20 times the mass of carbon in the atmosphere. This means that a relatively small release of methane from gas-hydrate systems could have significant impact.

The role of hydrates in the global carbon cycle and the sensitivity of the deep ocean temperature to surface climate change are questions that must be answered, according to a presentation at a methane hydrates workshop held by the International Institute for Applied Systems Analysis in July 2008.

The takeaway? Research needs to continue on these fascinating crystals, which can be both a hazard and a boon to an energy-hungry world.