“Public opinion is a major obstacle to underground CO2 storage”

The cap­ture and stor­age of car­bon diox­ide is a tech­no­logy that could make it pos­sible to con­tin­ue using fossil fuels dur­ing much of the 21^st cen­tury. It par­tic­u­larly con­cerns coal, a cent­ral resource for many coun­tries since there are still more than 2,500 thermal power plants in the world. This energy is used for the pro­duc­tion of elec­tri­city and heat (cogen­er­a­tion) for indus­tri­al and domest­ic pur­poses. Coal-fired and gas-fired thermal power plants are rel­at­ively abund­ant, afford­able, avail­able and loc­ated all over the world. As such, they strengthen the secur­ity and sta­bil­ity of energy systems.

Eco­nomy and demo­graph­ics being what they are, the energy trans­ition will take time – sev­er­al dec­ades at least. While we wait for the green hydro­gen eco­nomy, we must non­ethe­less con­tin­ue to live, all the while bat­tling against the green­house effect caused by CO₂ emis­sions. As such, car­bon cap­ture and stor­age offers a solu­tion to help buy us some valu­able time. CO₂ emis­sions rep­res­ent approx­im­ately 270 mil­lion tons every year but today only 0.1% of indus­tri­al emis­sions are cap­tured. Need­less to say, there is work to be done!

Nor­mally, under­ground stor­age of CO₂ is achieved through vari­ous meth­ods of phys­ic­al or chem­ic­al cap­ture, and it requires strict geo­lo­gic­al con­di­tions. As such, only very pre­cise geo­lo­gic­al envir­on­ments can be used. In par­tic­u­lar, the geo­lo­gic­al form­a­tions must not only be cap­able of con­tain­ing the CO₂ but must also pre­vent lat­er­al and/or ver­tic­al migra­tion of the gas. Any leaks could con­tam­in­ate pot­able ground­wa­ter at low depths, infilt­rate the ground, or more import­antly reach the atmosphere.

The geo­lo­gic­al form­a­tions used for CO₂ stor­age are mainly oil and gas reser­voirs, as well as deep saline aquifers found in sed­i­ment­ary basins. The stor­age of gas (includ­ing CO₂) in these envir­on­ments has been proven to work on a large scale. It can even be per­formed dur­ing oil extrac­tion oper­a­tions (sec­ond­ary recov­ery), nat­ur­al gas stor­age, and acid­ic gas removal.

Some of the risks asso­ci­ated with CO₂ cap­ture and stor­age are sim­il­ar and com­par­able to those of any oth­er indus­tri­al activ­ity for which safety and reg­u­lat­ory pro­to­cols are already estab­lished. At the moment, there are only few oper­a­tions in the world where CO₂ is injec­ted and stored in the ground (USA, Aus­tralia, Canada, China and UK). Most of the time, if not exclus­ively, it is done in the con­text of an oper­a­tion motiv­ated by drivers oth­er than cli­mate change, such as oil pro­duc­tion or reg­u­lat­ory require­ments for the use of hydro­gen sulf­ide (H₂S).

Exist­ing oper­a­tions show that there is no major tech­no­lo­gic­al obstacle for the geo­lo­gic­al stor­age of CO₂. Chal­lenges and blocks thus lie else­where. They mainly stem from the high cost of the oper­a­tion, par­tic­u­larly for diluted flows, like those from power plants and indus­tri­al com­bus­tion processes.

Spe­cif­ic risks asso­ci­ated with CO₂ stor­age relate to the oper­a­tion­al phase (the injec­tion, to put it simply) and the post-oper­a­tion­al phase. The greatest con­cern is linked with the pos­sible risk of CO₂ leak­age in the short or long term. Neg­at­ive effects include the glob­al cli­mate impact of the return of CO₂ in the atmo­sphere, as well as the loc­al health and envir­on­ment­al risks, which must there­fore be cor­rectly assessed and managed.

The oth­er obstacle is thereby more media-driv­en. We are con­cerned that pub­lic opin­ion might reject this tech­no­logy and that it could affect the large-scale imple­ment­a­tion of CO₂ geo­lo­gic­al stor­age. Indeed, who will accept such a stor­age site in their town? The risks asso­ci­ated with the trans­port­a­tion and injec­tion of car­bon diox­ide are reas­on­ably well under­stood. How­ever, there exists a small pos­sib­il­ity that the CO₂ stored under­ground could leak from a reser­voir, either by an uniden­ti­fied migra­tion path­way, or because of a well defect.

The threat that it could rep­res­ent must be assessed in com­par­is­on with vol­can­ic CO₂ emis­sions, which are nat­ur­al. Dif­fuse CO₂ emis­sions from the soil or via car­bon­ated sources in vol­can­ic areas do not seem to rep­res­ent a threat, provided that the CO₂ can dis­perse in the atmo­sphere. How­ever, CO₂ is dan­ger­ous when it accu­mu­lates in closed spaces. Thus, large clouds of CO₂ linked with sud­den emis­sions com­ing from vol­can­ic vents or craters are a deadly threat. The Lake Nyos dis­aster in 1986 in Cameroon, which res­ul­ted in 1,800 deaths from CO₂ asphyxi­ation, serves as a reminder.

Even if few ana­lo­gies exist between such an event and a pos­sible CO₂ leak from a reser­voir, the risk is not null. This dis­aster is there­fore likely to come up in the media and will arouse hos­til­ity in pop­u­la­tions liv­ing in prox­im­ity of a poten­tial stor­age site. Murphy’s law will pre­vail over any oth­er consideration.

In this case, only one option remains viable: stor­ing CO₂ in the open sea. In Europe, the Nor­we­gi­an Sea is often cited. How­ever, this does not mean that there would not be any impact in the event of a release of CO₂. Leak­age of gas under the sea would res­ult in water acid­i­fic­a­tion around the stor­age site, with pos­sible dam­age for fauna and flora close by. This has been examined in eco­tox­ic­o­logy stud­ies. But in any case, this CO₂ release – even in the event of a sig­ni­fic­ant leak – would not dir­ectly affect human health since it would be under the sea. This is there­fore reas­sur­ing for the pub­lic. Social accept­ance of this altern­at­ive is there­fore the only vari­able cap­able of accel­er­at­ing the imple­ment­a­tion of tech­no­lo­gies for redu­cing anthro­po­gen­ic CO₂ emis­sions in the atmosphere.