CAPTURE AND STORAGE OF CO2
If deep reductions in greenhouse gas emissions are required, (to meet the UNFCC goal of stabilisation of anthropogenic greenhouse gas emissions), then one method that could be used is CO2 capture and storage. CO2 capture and storage technology would be used in combination with the other mitigation measures (e.g. fuel switching, energy efficiency and renewable energy) to achieve the necessary deep reductions in greenhouse gas emissions.
CO2 can be captured from a variety of anthropogenic sources such as power plants and large industrial plants and then compressed and transported to a storage site. There are two potential storage options, which are;
- Storage in the oceans
- Storage in geological reservoirs
Currently, there are considerable uncertainties about the science of ocean storage. In addition, there are attendant legal issues that need to be addressed. Hence, ocean storage is less likely to be promoted as a mitigation option in the current situation.
However, geological of CO2 is a more promising storage option capable of achieving deep reductions in the foreseeable future. There are a number of potential geological formation that can be used to store captured CO2. These include;
- Depleted and disused oil and gas fields
- Deep saline aquifers
- Deep unminable coal seams
Many of these geological traps have already held hydrocarbons or liquids for many millions of years.
The global storage capacity for the main geological storage reservoirs has been estimated by the IEA Greenhouse Gas R&D Programme. In the Table below the storage capacities quoted are based on injection costs of up to 20 US $ per tonne of CO2 stored.
|Depleted gas fields
|Depleted oil fields/CO2-EOR
|Deep saline aquifers
|400 – 10 000
|Unminable coal seams
Table 1. Estimate of Storage Capacities for Different Geological Trap Types
The capacity estimates for these formations show that geological storage of CO2 can make a substantial impact on CO2 emissions reduction. From a capacity perspective, deep saline aquifers offer a very significant potential however, there is considerable uncertainty in the estimates for CO2 storage capacity in aquifers. Depleted oil and gas fields also have a significant storage potential. It must be noted that the storage potentials for oil and gas fields exclude fields that are not yet producing. Conversely, from a global perspective, storage of CO2 in deep unminable coals seams will not have a significant impact; however, there may well be some regional niche opportunities where its potential could be more significant.
The topic of CO2 capture and storage is currently the subject of a special report commissioned by the IPCC. This report will undertake a comprehensive review of the technical issues associated with CO2 capture and storage. The report is scheduled to be available in late 2005. Details can be found at: http://www.ipcc.ch/activity/sprep.htm.
The IEA Greenhouse Gas Programme is providing technical input to this report.