π Industry π Planet
Can we sweep our CO2 emissions under the rug?

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

Laurent Catoire, Head of Chemistry and Processes Unit at ENSTA Paris (IP Paris)
On March 8th, 2022 |
3 min reading time
Laurent Catoire
Laurent Catoire
Head of Chemistry and Processes Unit at ENSTA Paris (IP Paris)
Key takeaways
  • Every year, approximately 270 million tons of CO2 are emitted into the atmosphere: ~0,1% of which are currently captured.
  • The storage of CO2 emissions underground is done through various physical or chemical capture mechanisms in specific geological environments.
  • Existing operations show that there is no major technological obstacle for the geological storage of CO2.
  • The main issue would be acceptability. The possibility – however small – of CO2 leakage in the short or long-term poses a potential hazard to local populations.
  • Thus, for now, projects are focused on the storage of CO2 at sea, like the Norwegian Sea.

The cap­ture and stor­age of car­bon diox­ide is a tech­nol­o­gy that could make it pos­si­ble to con­tin­ue using fos­sil fuels dur­ing much of the 21st 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!

Storing CO2 underground

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).

A complicated start

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.

More acceptable solutions

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.


Laurent Catoire

Laurent Catoire

Head of Chemistry and Processes Unit at ENSTA Paris (IP Paris)

Laurent Catoire is a professor in applied chemical kinetics, in particular in combustion and in general in all reactive systems. After a DGA thesis, he has been working for 30 years on reactive systems that are little studied, poorly known but with important or potentially important applications (hypergolic systems in space propulsion, civil and military energetic materials (explosives, propellants and gas generators), energetic ionic liquids, nanothermites, aluminium combustion, metal combustion, etc).

Our world explained with science. Every week, in your inbox.

Get the newsletter