“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.