Methane hydrates: the next energy revolution?
Fire ice sounds like a magic trick, but it could be the next big energy breakthrough. Rhiannon Garth Jones finds out more.
North American shale gas has transformed the global energy scene. Yet the resource itself isn't new, just the technology to make its extraction commercially viable. Its success has spurred on other countries around the globe to find their own energy silver bullets, and methane hydrates, sometimes called ‘fire ice’, could be leading the pack.
What’s the story?
‘Gas hydrate’ is the term for a solid material formed from the combination of various gases and water. They are technically clathrate compounds – unique substances with no set chemical composition in which molecules of a host material form an open solid lattice that enclose, without direct chemical bonding, molecules of a guest material. The most common host is water and the most common guest is methane – hence ‘methane hydrate’.
These hydrates have been known to exist beneath the sea floor since the 1960s. Stored mostly in broad, shallow layers on continental margins, methane hydrate could exist in immense quantities – by some estimates, it is twice as abundant as all other fossil fuels combined (although there is great uncertainty about those numbers). Despite this, it isn’t a resource that has had much attention. The consensus for a long time was that the hydrates existed in large but low-concentration accumulations and so weren’t worth exploiting
That isn’t to say methane hydrates have been ignored – the US Department of Energy has been funding a methane-hydrate research programme since 1982, and Japan began a programme in 1995. Historically, Japan has had few natural resources of its own, and for decades has been reliant on nuclear energy. However, the Fukushima disaster and the subsequent costly LNG imports have increased Japan's focus on achieving energy independence by making the extraction of methane hydrates commercially viable.
Scientists from the Japan Oil, Gas, and Metals National Corporation (JOGMEC) have focused on the Nankai Trough, 200 miles southwest of Tokyo, and an undersea earthquake zone. Since 1999, they have been digging test wells, making measurements, and obtaining samples of the hydrate deposits – 130-foot layers of sand and silt, held together by methane-rich ice. In 2013, JOGMEC demonstrated gas recovery from deep-water methane hydrate deposits offshore.
In May 2016, it was reported at the Offshore Technology Conference (OTC) in Kuala Lumpur that a successful 2015 exploratory drilling programme had been conducted in the Bay of Bengal by the Indian National Gas Hydrates Program, using gas hydrate exploration approaches that had been developed and demonstrated in a landmark 2009 drilling programme conducted in the Gulf of Mexico by the US Department of Energy's National Energy Technology Laboratory.
Dr Ray Boswell, Technology Manager for Natural Gas Technology at the US Department of Energy, believes these programmes ‘have provided critical scientific information, but they remain limited in number and limited in their duration (commonly measured in days). Longer-duration scientific tests will be needed to assess methane hydrate’s resource potential. The progression of methane hydrates toward energy recovery will depend on the pace and results of research going forward and the varying need for new energy sources globally.’
George Hirasaki, Research Professor in Chemical & Biomolecular Engineering at Rice University, USA, was given a Heritage Award at the OTC for his extensive research on reservoir simulation, enhanced oil recovery and the detection and production of methane hydrates. He believes that, ‘This is a very large energy resource going into the future. There may not be too much interest to the USA because it has abundant natural gas that it can produce more cheaply, but in places like Japan, Korea, Taiwan and India that don't have their own resources – to them, it could be very valuable.’
What’s the problem?
‘Unlike conventional oil and gas’, Boswell explains, ‘which is stored under pressure that has to be controlled to enable safe and orderly production, gas hydrates are stored in a solid state in the Earth. Energy must be expended to dissociate the hydrate into oil and gas, however, any cessation in that energy input results in the virtually immediate re-solidification of the hydrate.’
As a result, the potential for uncontrolled releases is very low – the primary challenge is to keep the gas moving. Deep-water gas hydrates reside in relatively shallow sediments that are poorly consolidated. While the industry has a wealth of experience operating in such sediments (the North Sea, for example), such settings pose additional challenges in minimising seafloor subsidence. Substantial disturbance of the sediments overlying the hydrates could create pathways for unintended gas migration toward the seafloor.
‘For these reasons,’ Boswell said, ‘the 2013 offshore test by Japan featured extensive sea-floor and environmental monitoring technologies and the primary focus in the gas hydrate numerical simulation community is in fully integrated reservoir and seal geomechanics into predictions of reservoir flow. It is only through scientifically-focused field tests, that the basic issues of reservoir response and environmental implications will be understood.’
Well designs to make production commercially viable will face a number of challenges. It will primarily be a deep-water endeavour, which carries significant logistical and operating costs. The wells will be low pressure, making artificial lift necessary. The temperatures involved will be low enough to demand low assurance measures, as well as requiring careful monitoring during the endothermic process of gas hydrate dissociation.
How will it be done?
Initially, it was believed that methane hydrate extraction would require a traditional mining-related approach. However, the discovery of sand-hosted deep water hydrates over large, low-concentration, clay-hosted deposits means that existing drilling and production technologies could be used. Methane hydrate-bearing sand reservoirs that are the most deeply buried will be favoured, because of their warmer temperatures, greater mechanical stability and isolation from sensitive near-surface environments.
According to Boswell, of the various drilling-based approaches that have been considered, including injection of chemical inhibitors, thermal stimulation and reservoir depressurisation, the latter is currently considered to be the most promising.
Using conventional oil and gas methods, a wellbore is drilled and cased to establish a production well. That well is then perforated to enable communication with the gas-hydrate-bearing strata and fluids are pumped to the surface using down-hole pumps, which lowers the pressure in the well and creates a pressure gradient between the wellbore and the reservoir.
The production of mobile fluids in the reservoir transmits the pressure change, shifting the local region out of methane hydrate stability conditions and leading to the dissociation of gas hydrate into gas and water components. The established pressure gradient then directs the released gas and water to the wellbore, where they will be pumped to the surface.
The problem with every aspect of the methane hydrates story right now is that we don’t know enough. The potential safety concerns, barriers to commercial viability and even the size of the prize all remain unknown, as Boswell made clear, ‘There is much to be learned before it can be determined what share of that estimated volume might be commercially-viable energy targets’.
And there are other considerations – after COP21, how far should we pursue new methods of extracting fossil fuels? Should national governments who have committed to reducing their emissions provide the funding required to find the answers to those questions?
For the moment, governments are among those exploring the possibilities. And, while it appears that there are many obstacles to be overcome before we could see the kind of shift in the energy market that shale gas created, much of the development of methane hydrates so far mirrors that of shale – an unconventional resource presenting technical challenges for extraction, subject to scepticism from the industry and controversy outside of it. Fire ice could be worth keeping an eye on.