Carbon Capture and Storage - Leakage

Leakage

A major concern with CCS is whether leakage of stored CO₂ will compromise CCS as a climate change mitigation option. For well-selected, designed and managed geological storage sites, IPCC estimates that risks are comparable to those associated with current hydrocarbon activity. Although some question this assumption as arbitrary citing a lack of experience in such long term storage. CO₂ could be trapped for millions of years, and although some leakage occurs upwards through the soil, well selected storage sites are likely to retain over 99% of the injected CO₂ over 1000 years. Leakage through the injection pipe is a greater risk.

Although the injection pipe is usually protected with non-return valves to prevent release on a power outage, there is still a risk that the pipe itself could tear and leak due to the pressure. The Berkel en Rodenrijs incident in December 2008 was an example, where a modest release of CO₂ from a pipeline under a bridge resulted in the deaths of some ducks sheltering there. In order to measure accidental carbon releases more accurately and decrease the risk of fatalities through this type of leakage, the implementation of CO₂ alert meters around the project perimeter has been proposed. Malfunction of a carbon dioxide industrial fire suppression system in a large warehouse released CO2 and 14 citizens collapsed on the nearby public road. A release of CO2 from a salt mine killed a person at distance 300 m

In 1986 a large leakage of naturally sequestered CO₂ rose from Lake Nyos in Cameroon and asphyxiated 1,700 people. While the carbon had been sequestered naturally, some point to the event as evidence for the potentially catastrophic effects of sequestering carbon artificially. The Lake Nyos disaster resulted from a volcanic event, which very suddenly released as much as a cubic kilometre of CO₂ gas from a pool of naturally occurring CO₂ under the lake in a deep narrow valley. The location of this pool of CO₂ is not a place where man can inject or store CO₂, and this pool was not known about nor monitored until after the occurrence of the natural disaster.

For ocean storage, the retention of CO₂ would depend on the depth. The IPCC estimates 30–85% of the sequestered carbon dioxide would be retained after 500 years for depths 1000–3000 m. Mineral storage is not regarded as having any risks of leakage. The IPCC recommends that limits be set to the amount of leakage that can take place. This might rule out deep ocean storage as an option.

It should be noted that at the conditions of the deeper oceans, (about 400 bar or 40 MPa, 280 K) water–CO₂(l) mixing is very low (where carbonate formation/acidification is the rate limiting step), but the formation of water-CO₂ hydrates, a kind of solid water cage that surrounds the CO₂, is favorable.

To further investigate the safety of CO₂ sequestration, Norway's Sleipner gas field can be studied, as it is the oldest plant that stores CO₂ on an industrial scale. According to an environmental assessment of the gas field which was conducted after ten years of operation, the author affirmed that geosequestration of CO₂ was the most definite form of permanent geological storage of CO₂:

Available geological information shows absence of major tectonic events after the deposition of the Utsira formation . This implies that the geological environment is tectonically stable and a site suitable for carbon dioxide storage. The solubility trapping the most permanent and secure form of geological storage.

In March 2009 StatoilHydro issued a study showing the slow spread of CO₂ in the formation after more than 10 years operation.

Phase I of the Weyburn-Midale Carbon Dioxide Project in Weyburn, Saskatchewan, Canada has determined that the likelihood of stored CO₂ release is less than one percent in 5,000 years. A January 2011 report, however, claimed evidence of leakage in land above that project. This report was strongly refuted by the IEAGHG Weyburn-Midale CO₂ Monitoring and Storage Project, which issued an eight page analysis of the study, claiming that it showed no evidence of leakage from the reservoir.

Detailed geological histories of basins are required and should utilize the multi-billion dollar petroleum seismic data sets to decrease the risk associated with fault stability. On injection of CO₂ into the earth, there is a major pressure front that can break the seal and make faults unstable. The Gippsland Basin in Australia has a 3D-GEO seismic megavolume that consists of 30+ 3D seismic volumes that have been merged. Such data-sets can image faults at a resolution of 15 meters over an area 62 miles (100 km) by 62 miles (100 km). By mid 2010 the first full geological study of the Gippsland Basin will become openfile by 3D-GEO, making CCS fault risk workflow available with the associated data that constrains it. In other basins around the world, such studies are not available and can only be bought at a price tag of greater than a million dollars.

The liability of potential leak(s) is one of the largest barriers to large-scale CCS.