17. How much CO2 can be stored at different locations?

The amount of CO2 that can be injected and stored in a geological formation is different for every site. Storage capacity depends on the porosity and permeability characteristics of the individual rock formations. Porosity refers to the measurement of the number of void spaces in a rock or material. Permeability refers to the ability of the rock to allow for the injection and passing of fluids. How much carbon dioxide can be stored and how fast it can be injected are tied to these two concepts.

The amount of CO2 that can be injected also depends on the number and arrangement of the injection wells. For example, at the Weyburn and Midale oilfields, the porosity and permeability are not as high as in a saline sandstone formation. In addition, many wells are used to inject the carbon dioxide into the oilfields, because the CO2 is being used to recover oil (EOR) and not primarily for storage. In a project, however, that is solely about storing CO2 in a deep saline formation, or some other highly permeable location, fewer wells for injection would be required. This is the main difference between CO2 injection at Weyburn and Midale, which is used to recover oil, and CO2 injection in other projects that are purely for storage.

Deep saline formations that are chosen for storage sites are usually very large and therefore have a capacity to store CO2 in thetens-to-hundreds of millions of tonnes. These geological formations are made up of highly porous and permeable rocks (most often sandstone) that contain very salty water. Because these types of formations are so vast in size and are highly permeable and porous, very large volumes of CO2 can be injected and stored using far fewer injection points, and without a significant increase of pressure in the formation. Globally these types of formations have been estimated by the International Panel on Climate Change (IPCC) to have a storage capacity of up to 10,000 gigatonnes (Figure 13).

Figure 13.Estimated total storage potential for CO2, worldwide. The 104 in the chart's right hand column refers to 10,000. (From www.ipcc.ch/pdf/special-reports/srccs/srccs_chapter5.pdf)

The IPCC estimates that there is potentially enough storage space in deep saline formations to store all the manmade CO2 from large fixed sources for approximately 600 years.

The WMP did not examine the storage of CO2 in a deep saline formation, but rather in an oil reservoir. Oil and gas reservoirs are also excellent places for storing CO2 because they are like saline formations where naturally occurring gases and fluids have been trapped and stored for tens of millions of years. Their total CO2 storage volumes are dependent on the unique characteristics of each reservoir. The Weyburn field will have stored 30 million tonnes of CO2 by the end of the oil production life of the field, but it has been estimated that an additional 25 million tonnes could be injected safely into the reservoir (see Figure 14). Right now, the oil company operating the Weyburn field is injecting CO2 strictly to increase oil production. By the end of the production life of the oilfield (the point where recovery of oil will no longer be economically viable), the operator could continue to inject CO2 into the reservoir up to a total of 55 million tonnes. Figure 14 shows the point, in 2035, at which the field will no longer be producing oil. At that time, the Weyburn field could continue to receive CO2 but only for storage purposes, not for enhanced oil recovery.

Figure 14. Estimated total CO2 storage potential in just the Weyburn oilfield at the end of EOR operations. The field has the potential to hold an additional 25 MT of CO2 after the 30 MT that will have been injected at the end of EOR. The Midale field, not shown here, will hold an estimated additional 10 MT by the end of EOR. (Image courtesy of IEAGHG)