What is it?
Methane hydrate (also known as methane clathrate) is an ice-like form of concentrated methane and water found in the sediments of permafrost regions and marine continental margins at depths far shallower than conventional oil and gas.
Despite their relative accessibility and widespread occurrence, methane hydrates have rarely been tapped to meet increasing global energy demands.
With rising natural gas prices, production from these unconventional gas deposits is becoming economically viable, particularly in permafrost areas already being exploited for conventional oil and gas.
There is one example of long-term methane hydrate exploitation that demonstrates the viability of this resource as a fuel for power plants:
Deep in the Arctic Circle, in the Messoyakha gas field of western Siberia, lies a pioneer in methane hydrate extraction. Back in 1967, Russian engineers began pumping natural gas from beneath the permafrost and piping it east across the tundra to the Norilsk metal smelter, the biggest industrial enterprise in the Arctic. In 1978 they decided to wind down the operation. According to their surveys, they had sapped nearly all the methane from the deposit. But despite their estimates, the gas just kept on coming. The gas field was re-opened and continues to power Norilsk today.
- Where was this methane coming from?
- Russian geologists initially thought it was leaking from another deposit hidden beneath the first. But their experiments revealed the opposite -- the mystery methane was seeping into the well from the icy permafrost above. If unintentionally, what they had achieved was the first, and so far only, successful exploitation of methane hydrate. Made of molecules of methane trapped within ice crystals, this stuff looks like dirty ice and has the consistency of sorbet. Touch it with a lit match, though, and it bursts into flames.
- So what are methane hydrates, and where do they come from?
- As with all natural gas, the story starts with rotting plants. As these plants decay, they release methane, which permeates through porous rocks underground. If the conditions where the methane ends up are just right -- temperatures close to 0 degrees Celsius and pressures of roughly 50 atmospheres -- ice crystals form that trap the gas in place.
- In practice, these conditions mostly occur within and underneath permafrost and beneath the seabed on continental shelves, usually at ocean depths of 200 to 400 meters, although hydrates have also been known to appear on the seabed. In 2000, a 1-ton chunk of the stuff was scooped up by fishermen off Vancouver Island in British Columbia. They hastily dumped the hissing mass back into the ocean.
- Discovery Through Research
- Until recently, these deposits escaped the serious attention of most energy companies. Engineers stumbled on hydrates from time to time while drilling for conventional reserves of oil and gas, but they were mostly viewed as an irritant that caused blowouts or blocked pipelines.
- That view changed with studies showing that the gas is often present at a given site in concentrations of 50 % or more in ice's pore space -- values similar to the prevalence of natural gas in traditional sources -- in layers of hydrate hundreds of meters thick. What's more, in its constricted surroundings the gas is compressed to 160 times its density at atmospheric temperature and pressure, making for vast quantities of it when released.
- These revelations made hydrates a potential gold mine that countries and energy companies are now eagerly prospecting. In 2007, a US project found clathrate reserves in Alaska with 80 % of the ice's pore space packed with methane. Tim Collett, a clathrate specialist at the US Geological Survey who was part of the team, says there may be reserves all along the Alaska North Slope, including beneath existing oil installations at Prudhoe Bay and, alarmingly for environmentalists, the Arctic National Wildlife Refuge. Collett estimates there is between 0.7 and 4.4 tcm of methane hydrate in Alaska alone. Even the low end of that range could heat 100 mm homes for a decade.
- That's not the only reserve of interest. In 2004, a German and Chinese team found methane venting from the seabed off the coast of Taiwan in the South China Sea, and in 2006 Indian researchers found a layer of methane clathrates 130 meters thick off its east coast in an area known as the Krishna-Godavari basin. Collett calls these "one of the world's richest marine gas hydrate accumulations".
- Estimates vary, but conservative figures place global reserves at roughly 3 trillion tons of previously untapped carbon -- more than is trapped in all the other known fossil fuel reserves put together, says Klaus Wallmann of the Leibniz Institute of Marine Science in Kiel, Germany.
- That would last about 1,000 years if we continue to use natural gas at the current rate. Even if the methane from hydrates replaced all fossil fuels, and not just gas, it would still last for at least 100 years. But with this methane held in fragile ice crystals and buried deep within the Earth, can it be exploited safely and economically?
- Obtaining Methane Hydrate
- Until recently, there were two methods of extracting methane from hydrates from offshore locations that were considered feasible. One is to drill a hole into the hydrate deposit to release the pressure, allowing the methane to separate out from the clathrate and flow up the wellhead. The second is to warm the hydrate by pumping in steam or hot water, again releasing the methane from its icy matrix.
- In 2002, Canadian, American, Japanese, Indian and German researchers tested both techniques in the field, at a drill site called Mallik on the outer extremity of the Mackenzie river delta in the Canadian Arctic. Both were successful, but the energy costs of the heating method nearly outweighed the energy gained from the methane released, making depressurisation the more attractive option.
- The potential of depressurisation was confirmed in March 2008, when Canadian engineers led by Scott Dallimore of the Geological Survey of Canada used the technique to tap 20,000 cm of methane gas over six days from a deposit located 1 km beneath Mallik.
- Similarly, in 2007, South Korea exploited depressurisation to extract methane hydrate from the Ulleung basin in the Sea of Japan. Officials believe reserves there could meet the country's gas needs for up to 30 years, and they plan to begin production by 2015. Meanwhile Japan, another country with limited fossil fuel reserves, has found up to 50 trillion cubic meters of hydrate south-east of Honshu Island in the Nankai trough -- enough to supply the country with natural gas for centuries. In March 2008, the Japanese cabinet pledged to begin production by 2016.
- Risks and Solutions
- So methane hydrate extraction seems to be imminent, in Asia at least. Whether it is desirable is another matter. Some argue that the world shouldn't be tapping a new fossil fuel while governments are pledging to build a low-carbon economy. Methane might be less carbon intensive than fuels such as coal, but switching to methane would not help countries to reach ambitious targets for reducing carbon emissions of up to 80 % by 2050.
- To make matters worse, the methane itself could exacerbate global warming if it starts leaking from the reserves. Methane is, molecule for molecule, 20 times as powerful at warming the air as CO2. Rising sea temperatures could melt some undersea hydrate reserves even without extraction projects disturbing them, triggering a release of this potent greenhouse gas.
- Exploitation of hydrate reserves might exacerbate this problem, but it could also have far more immediate adverse effects. It is specifically this hazard that has led to a decision by Tundra Gas to not pursue undersea methane hydrate deposits even though they appear to be "easier" and cheaper to exploit.
- Many geologists suspect that gas hydrates play an important role in stabilizing the sea floor. Drilling in these oceanic deposits could destabilize the seabed, causing vast swaths of sediment to slide for kilometers down the continental slope. Evidence suggests that such underwater landslides have occurred in the past with devastating consequences. The movement of so much sediment would certainly trigger massive tsunamis similar to those seen in the Indian Ocean tsunami of December 2004.
- Hydrates exist in a delicate balance, and the worry is that as gas is extracted its pressure will break up neighboring hydrate crystals. The result could be an uncontrollable chain reaction -- a "methane burp" that could cascade through undersea reserves, triggering landslips and even tsunamis.
- "Extraction increases the risk of large-scale collapses, which might have catastrophic consequences," says Geir Erlsand from the University of Bergen in Norway.
- Among the evidence that such events have happened in the past is the the Storegga slide, a landslip on the seabed off western Norway about 8,000 years old. A 400-km stretch of submarine cliff on the edge of the continental shelf collapsed into the deep ocean, taking with it a staggering 3,500 cubic km of sediment that spread across an area the size of Scotland. The result would have been a tsunami comparable to the one that devastated parts of south-east Asia in 2004.
- The naval researchers who first discovered the remains of the slide in 1979 assumed it was the result of an earthquake. Perhaps it was initially, but Juergen Mienert of the University of Tromso in Norway has found that the slumped area was also a hotspot for methane clathrates. The sheer number of cracks and giant pockmarks on the seabed, carbon-dated to the time of the slide, suggest billions of tons of methane must have burst out of the cliff along with the sediment, a possible trigger for the landslip. The resulting explosions would have turned even a minor slip into a major disaster.
- The Storegga slide is not the only incident of this kind. The ocean floor from Storegga to Svalbard is full of pockmarks that might have been caused by similar clathrate-driven landslides.
- There might in fact be a safer way of tapping hydrates which, if successful, could allay the fears of most geologists. Since other gases can also form clathrates, it should be possible to pump one of these gases into the crystals to displace the methane. Carbon dioxide would be an ideal candidate - the resulting crystal is even more stable than methane clathrate/hydrate, meaning another greenhouse gas would be stored out of harm's way. This technique has already been demonstrated in the lab. In joint research with the energy company ConocoPhillips based in Houston, Texas, Geir Ersland replaced methane with CO2 in artificial clathrate crystals. The exchange was rapid and did not damage the clathrate structure, making it the safest way to extract the methane yet found (Chemical Engineering Journal, DOI: 10.1016/j.cej.2008.12.028). Substituting methane with CO2 "will increase the stability of the reservoir sediments as well as maintaining the clathrates in their solid state", Ersland says.
- The Future
- It is an intriguing possibility. Sooner rather than later, burning fossil fuels like coal and natural gas will only be acceptable if the CO2 emissions are captured and stored. Right now, there is a rush to develop a practical system for capturing and burying billions of tons of CO2 underground per year. So far, the focus has been on old oil wells, salt deposits and even old coal mines. The big problem is that the huge infrastructure required to dispose of the CO2 may quickly make burning fossil fuels uneconomic compared with alternatives like solar, wind or nuclear power. Disposing of CO2 down the same pipe used to bring up more fuel could be the answer.
- If this technology is successfully implemented i.e. if it is safe, environment-friendly and cost-effective, Tundra Gas will look again and undersea methane hydrates extraction. But as it might take more than a decade to develop a suitable system that will satisfy gas companies, environmentalists and governments, we intend to focus on methane hydrates deposits in permafrost zones in the northern hemisphere using proven recovery techniques. For more information, please visit our Business Outline page.