Carbon Dioxide Hyrdates Could Secure Sub-Sea Sequestration
18 March 2006
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| To understand their properties researchers are studying how hydrates grow in sediment pore space at the scale of individual crystals. Follow-up work will be done on full-size sediment cores. Source: EPSRC |
Capturing and storing carbon dioxide produced by the generation of power and production of synthetic fuels is a critical component in plans to reduce the rate of anthropogenic climate change. Depleted off-shore oil fields are primary targets for CO2 storage, with the accompanying prospect of enhanced oil recovery (earlier post.) Yet the concern remains: what if the CO2 leaks back out?
A team at the Center for Gas Hydrate Research at Heriot-Watt University in the UK is investigating a natural physical process that could help secure carbone dioxide captured and sequestered in the sub-seabed.
In some conditions, seawater and carbon dioxide could combine into carbon dioxide ice-like compounds—carbon dioxide hydrates—in which the water molecules form cavities that act as cages, trapping the carbon dioxide molecules. In the event of carbon dioxide starting to leak into the sea from an under-seabed disposal site (e.g., a depleted North Sea oil or gas reservoir), this process could add a second line of defense preventing the escape of the gas.
As the leaking carbon dioxide comes into contact with the seawater in the pores of seafloor sediments above it, the formation of carbon dioxide hydrates would form create a secondary seal, blocking sediment pores and cracks, and slowing or preventing leakage of the carbon dioxide.
We want to identify the type of seabed locations where sediment, temperature and pressure are conducive to the formation of carbon dioxide hydrates. This data can then be used to help identify the securest locations for carbon dioxide storage and can aid in the development of methods for monitoring potential CO2 leakage. In the future, it may even be possible to manipulate the system to promote CO2 hydrate formation, extending the number of maximum-security sites that are available.
—Professor Bahman Tohidi, project leader
The research team is examining exactly how and where hydrates form, and establishing the optimum conditions that enable this process to take place. Their work includes the use of an experimental facility to simulate conditions in different sub-seabed environments with different types of sediment, and to observe hydrate formation when carbon dioxide is introduced. They have also developed tiny 2-dimensional sediment micromodels (layers of glass etched with acid to simulate sediments) to help explore how hydrate crystals grow at pore scale in seafloor sediments.
The 3-year research project “Can CO2 Hydrate Formation Act as a Safety Factor for Subsurface Storage of CO2?” is due to run until September 2008. The UK’s Engineering and Physical Sciences Research Council EPSRC is providing funding of nearly £298,000 (US$523,000) in support of the project.
Sounds interesting, but I reckon CO2 is best sequestered in biomass, if only because this can be used to close the loop. The trick is manipulating (the energy from) sunlight such that you can achieve useful rates with moderate land resources. That means using thin plate bioreactor stacks with efficient round-the-clock artificial lighting using electricity generated from renewable sources.
Hydrates are also prone to rapid outgassing if the pressure drops - which it will, once outgassing starts! This is a major reason why the huge methane reserves trapped in natural suboceanic hydrate deposits have not yet been commercially tapped.
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