Methane Hydrate – Ice on Fire
Deep in the Arctic Circle, in the Messoyakha gas field of western Siberia, lies a mystery. Back in 1970, Russian engineers began pumping natural gas from beneath the permafrost. The field continues to power Norilsk today.
Ice on fire: The next fossil fuel (2009)
By Fred Pearce: Deep in the Arctic Circle, in the Messoyakha gas field of western Siberia, lies a mystery. Back in 1970, 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. By the late 70s, they were on the brink of winding 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 field continues to power Norilsk today.
Until recently, there were two methods of extracting methane from clathrates that were considered feasible. One is to drill a hole into the clathrates deposit to release the pressure, allowing the methane to separate out from the clathrates and flow up the wellhead. The second is to warm the clathrate 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.
To make matters worse, the methane itself could exacerbate global warming if it starts leaking from the reserves. Rising sea temperatures could melt some undersea clathrate reserves even without extraction projects disturbing them, triggering a release of this potent greenhouse gas. A decade ago, Peter Brewer of the Monterey Bay Aquarium Research Institute in Moss Landing, California, showed how clathrates on the seabed just off the coast of California disappeared after an El Niño event raised ocean temperatures by 1 °C. Exploitation of clathrates reserves might exacerbate this problem, but it could also have far more immediate adverse effects. Clathrates exist in a delicate balance, and the worry is that as gas is extracted its pressure will break up neighbouring clathrate 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.
Evidence that such events have happened in the past comes from the Storegga slide, a landslip on the seabed off western Norway about 8000 years ago. A 400-kilometre stretch of submarine cliff on the edge of the continental shelf collapsed into the deep ocean, taking with it a staggering 3500 cubic kilometres 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 Jürgen Mienert of the University of Tromsø 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 tonnes 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, says Mienert. He says we will see more of these events in the future. “Global warming will cause more blowouts and more craters and more releases,” he warns. There might in fact be a safer way of tapping clathrates which, if successful, could quash the criticisms. 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, says Ersland – the resulting crystal is even more stable than methane clathrate, meaning another greenhouse gas would be stored out of harm’s way.
Ersland has already demonstrated his technique in the lab. In joint research with the energy company ConocoPhillips based in Houston, Texas, he 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).
Next major energy resource: Japan the first country to succeed in Extracting fuel from Fire Ice (2013)
Japan has become the first country in the world to succeed in extracting methane gas from a previously untapped off-shore fossil fuel resource that has been dubbed ‘fire ice’. Methane hydrate, a sherbet-like substance buried beneath continental shelves around the world, has been tipped by energy experts to be the next major energy resource.
Consisting of methane trapped in ice, it was previously believed to only exist in the outer reaches of the solar system – but now scientists are saying it could be ‘the new shale gas’. State-run Japan Oil, Gas and Metals National Corp (JOGMEC) said the gas was tapped from deposits of methane hydrate near the country’s central coast.
A Japanese study has estimated the existence of at least 40 trillion cubic feet (1.1 trillion cubic metres) of methane hydrates in the eastern Nankai Trough off the country’s Pacific coast. Source
Data from Innovative Methane Hydrate Test on Alaska’s North Slope
NETL, the research laboratory of DOE’s Office of Fossil Energy (FE), participated in gas hydrate field production trials in early 2012 in partnership with ConocoPhillips and the Japan Oil, Gas and Metals National Corp. (JOGMEC). This test well (known as Iġnik Sikumi, Inupiat for “Fire in the Ice”) represented the first test of a CO2 exchange technology that was developed by ConocoPhillips and the University of Bergen, Norway. In the test, a small volume of CO2 and nitrogen was injected into the well and then the well was produced back to demonstrate that this mixture of injected gases could promote production of natural gas.
Both the U.S. and Japan have committed to utilizing Arctic gas hydrate research opportunities as an important step in assessing the potential for gas hydrate production in deepwater marine settings, the location of the vast majority of global resources. DOE and JOGMEC have also collaborated on the development of specialized core sampling devices through the Gulf of Mexico Gas Hydrates Joint Industry Project (an industry consortium managed by Chevron) conducting research on deepwater gas hydrate characterization technology. Source
Related
Flow Test from Methane Hydrate Layers Ends: From June to July, the pressured core samples were acquired from methane hydrate layers. In this operation, a flow test through dissociation of methane hydrate was begun on March 12 after the preparatory works including drilling and installing equipments. JOGMEC has been conducting gas production until now. However, it ended the flow test today on March 18 since changes in well situation, including tentative malfunction of the pump to draw water for depressurization and simultaneous increase in sand production, have been seen and a rough weather was forecasted.
Although the detailed analysis will be conducted from now on, JOGMEC has obtained necessary data for promoting future research and development of methane hydrate until now including gas production and its continuous production from methane hydrate layers under the sea by depressurization method, confirmation of indications that dissociation of methane hydrate has reached to monitoring wells which locate approximately 20m from the production well.
Why are Gas Hydrates Important?
Centre for Gas Hydrate Research: Gas hydrates are of great importance for a variety of reasons. In offshore hydrocarbon drilling and production operations, gas hydrates cause major, and potentially hazardous flow assurance problems.
Naturally occuring methane clathrates are of great significance in their potential for as strategic energy reserve, the possibilities for CO2 disposal by sequestration, increasing awareness of the relationship between hydrates and subsea slope stability, the potential dangers posed to deepwater drilling installations, pipelines and subsea cables, and long-term considerations with respect to hydrate stability, methane (a potent greenhouse gas) release, and global climate change.
What could possibly go wrong? So is Japan caging CO2 inside the clathrates while tapping a very unstable energy source?
Hydrates in Offshore Hydrocarbon Production Operations Drilling
In drilling, record water depths are continuously being set by oil companies in the search of hydrocarbon reserves in deep waters. Due to environmental concerns and restrictions, water based drilling fluids are often more desirable than oil based fluids, especially in offshore exploration. However, a well-recognised hazard in deep water offshore drilling, using water based fluids, is the formation of gas hydrates in the event of a gas kick.
In deep-water drilling, the hydrostatic pressure of the column of drilling fluid and the relatively low seabed temperature, could provide suitable thermodynamic conditions for the formation of hydrates in the event of a gas kick. This can cause serious well safety and control problems during the containment of the kick. Hydrate formation incidents during deep-water drilling are rarely reported in the literature, partly because they are not recognised, Two cases have been reported in the literature where the losses in rig time were 70 and 50 days.
The formation of gas hydrates in water based drilling fluids could cause problems in at least two ways:
- Gas hydrates could form in the drill string, blow-out preventer (BOP) stack, choke and kill line. This could result in potentially hazardous conditions, i.e., flow blockage, hindrance to drill string movement, loss of circulation, and even abandonment of the well.
- As gas hydrates consist of more than 85 % water, their formation could remove significant amounts of water from the drilling fluids, changing the properties of the fluid. This could result in salt precipitation, an increase in fluid weight, or the formation of a solid plug.
- The hydrate formation condition of a kick depends on the composition of the kick gas as well as the pressure and temperature of the system. As a rule of thumb, the inhibition effect of a saturated saline solution would not be adequate for avoiding hydrate formation in water depth greater than 1000 m. Therefore, a combination of salts and chemical inhibitors, which could provide the required inhibition, could be used to avoid hydrate formation.
Production
The ongoing development of offshore marginal oil and gas fields increases the risks of facing operational difficulties caused by the presence of gas hydrates. A typical area of concern is multiphase transfer lines from well-head to the production platform where low seabed temperatures and high operation pressures increase the risk of blockage due to gas hydrate formation. Other facilities, such as wells and process equipment, can also be prone to hydrate formation.
Different methods are currently in use for reducing hydrate problems in hydrocarbon transferlines and process facilities. The most practical methods are:
- At fixed pressure, operating at temperatures above the hydrate formation temperature. This can be achieved by insulation or heating of the equipment.
- At fixed temperature, operating at pressures below hydrate formation pressure.
- Dehydration, i.e., reducing water concentration to an extent of avoiding hydrate formation.
- Inhibition of the hydrate formation conditions by using chemicals such as methanol and salts.
- Changing the feed composition by reducing the hydrate forming compounds or adding non hydrate forming compounds.
- Preventing, or delaying hydrate formation by adding kinetic inhibitors.
- Preventing hydrate clustering by using hydrate growth modifiers or coating of working surfaces with hydrophobic substances.
- Preventing, or delaying hydrate formation by adding kinetic inhibitors.
One interesting branch of research in this area is the possibility of CO2 sequestration. CO2 hydrate is thermodynamically more stable than methane hydrate, so the possibility exists for sequestration of CO2 into existing seafloor clathrates, whereby yielding methane. This process is particularly attractive, as it would act as both a source and a sink with respect to greenhouse gas emissions.
Hydrates as a Geohazard
The aspect of gas hydrates which has the biggest implications for human welfare at present, is their potential as a geohazard. Of particular concern is the danger posed to deepwater drilling and production operations, and the large body of evidence which now exists linking gas hydrates with seafloor stability.
With conventional oil and gas exploration extending into progressively deeper waters, the potential hazard gas hydrates pose to operations is gaining increasing recognition. Hazards can be considered as arising from two possible events: (1) the release of over-pressured gas (or fluids) trapped below the zone of hydrate stability, or (2) destabilization of in-situ hydrates.
The presence of BSRs has previously been a cause of concern, as they could be considered evidence for the existence of free gas (possibly at high-pressure) beneath the HSZ. More recent analysis suggests however, that as long as excess water is present, there should not be a build-up of gas pressure beneath the HSZ. This is because, at the base of hydrate stability, the system approximates to 3-phase equilibrium, where pressure is fixed (generally at hydrostatic), and temperature occupies the available degree of freedom. This means that any excess gas will be converted to hydrate, returning the system to its equilibrium pressure (assuming there is no major barrier to the mass transfer of salt). This case is likely to predominate in many hydrate-bearing sediments, although gas seeps and mud volcanoes, common to thermogenic hydrate areas (e.g. Gulf of Mexico, Caspian Sea), could be considered evidence for excess gas and pore-fluid pressures at shallow depths.
In the absence of gas traps, hydrates still pose a hazard due to their potential for destabilization. This danger is particularly apparent in the case of conventional oil and gas exploration, for which drilling methods contrast quite markedly to the shallow piston-coring approach used by ODP in hydrate areas.
Conventional rotary drilling operations could cause rapid pressure, temperature or chemical changes in the surrounding sediment. An increase in temperature could be caused by a hot drill bit, warm drilling fluids, or later as
high-temperature reservoir fluids rise through the well, while the addition of hydrate inhibitors to drilling muds (to prevent hydrate formation in the well-bore or drill string in the event of a gas-kick) could change sediment pore-fluid chemistry. Some, or all of these changes, could result in localized dissociation of gas hydrates in sediments surrounding wells. A similar case would apply to seafloor pipelines, where the transportation of hot fluids could cause dissociation of hydrates in proximal sediments. In a worst-case scenario, clathrate dissociation could lead to catastrophic gas release, and/or destabilization of the seafloor.
The hazards associated with drilling in gas hydrate areas are exemplified by cases from the Alaskan Arctic, where subsurface permafrost hydrate destabilization has resulted in gas kicks, blowouts, and even fires.
Hydrates and Seafloor Stability
A significant part of the gas hydrate geohazard problem is related to how they alter the physical properties of a sediment. If no hydrate is present, fluids and gas are generally free to migrate within the pore space of sediments. However, the growth of hydrates converts what was a previously a liquid phase into a solid, reducing permeability, and restricting the normal processes of sediment consolidation, fluid expulsion and cementation. These processes can be largely stalled until the BHSZ is reached, where hydrate dissociation will occur. Dissociation of hydrates at the BHSZ can arise through an increase in temperature due to increasing burial depth (assuming continued sedimentation) or an increase in sea bottom-water temperatures, and/or a decrease in pressure (e.g., lowering of sea level). Upon dissociation, what was once solid hydrate will become liquid water and gas. This could lead to increased pore-fluid pressures in under-consolidated sediments, with a reduced cohesive strength compared to overlying hydrate-bearing sediments, forming a zone of weakness. This zone of weakness could act as a site of failure in the event of increased gravitational loading or seismic activity.
The link between seafloor failure and gas hydrate destabilization is a well established phenomenon, particularly in relation to previous glacial-interglacial eustatic sea-level changes. Slope failure can be considered to pose a significant hazard to underwater installations, pipelines and cables, and, in extreme cases, to coastal populations through the generation of tsunamis.
Hydrates and Global Climate Change
Methane is a particularly strong greenhouse gas, being ten times more potent than carbon dioxide. Increasing evidence points to the periodic massive release of methane into the atmosphere over geological timescales. However, whether such enormous releases of methane are a cause or an effect with respect to global climate chnages remains the subject of much debate.
Global warming may cause hydrate destabilsation and gas release through a rise in ocean bottom water temperatures. Methane release in turn would be expected to accelerate warming, causing further dissociation, potentially resulting in run away global warming. However, coversely, sea level rise during warm periods may act to stabilise hydrates by increasing hydrostatic pressure, acting as a check on warming.
A further possiblity is that hydrate dissociaton may act as a check on glaciation, whereby reduced sea levels (due to the growth of ice sheets) may cause seafloor hydrate dissociation, releasing methane and warming the climate.
The strong link between naturally occurring gas hydrates and the Earth’s climate is an increasingly recognised phenomenon.
Background information
The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water, though this is dependent on how many methane molecules “fit” into the various cage structures of the water lattice. The observed density is around 0.9 g/cm3. One litre of methane clathrate solid would therefore contain, on average, 168 litres of methane gas (at STP). Source
About the Author: Chris Machens
