Definition :
The depleted Oil & Gas CO2 storage consist in injecting pure CO2 in depleted Oil & Gas reservoirs with adapted monitoring to ensure no leaks.
For now, the guaranteed storage period is 100 years without leaks but could be guaranteed for longer time with appropriate monitoring. CO2 injection in depleted Oil & Gas reservoirs are mastered mainly by Oil & Gas companies such as Occidental Petroleum (Oxy) or Total. In most Oil & Gas geologic formation, there is few reactive rock to convert the CO2 to mineral and thus the CO2 will remain gaseous, lighter than water with a tendency to go up and thus will a risk of medium to long term release (through the injection pipe). Some accidents have already occurred causing casualties after pure CO2 release, not yet due to CO2 sequestration but the risk exists and should be considered.
The cost of storage varies from 1$ / tCO2 to 7$ / tCO2 for on shore storage. However, regulations tend to forbid on shore storage due to risks of pure CO2 leaks and thus off shore storage may be preferred but at a higher cost between 2$ / tCO2 and 14$ / tCO2.^2
Datas : Technical data was found in ^3.
^1: Scottish Centre for Carbon Storage, 2012, https://www.researchgate.net/figure/Injection-of-carbon-dioxide-into-depleted-oil-and-gas-reservoir-Image-source-Scottish_fig13_327750644 ^2: Global CCS institute, https://www.globalccsinstitute.com/archive/hub/publications/119816/costs-co2-storage-post-demonstration-ccs-eu.pdf ^3: Fasihi, M., Efimova, O. and Breyer, C., 2019. Techno-economic assessment of CO2 direct air capture plants. Journal of cleaner production, 224, pp.957-980.