Geological Storage of CO2

350 PPM is the safe limit of CO2 for humans; however, we have passed 400 PPM for quite some time. Now we must be in firefighting mode to remove CO2 from atmosphere by whatsoever means available as on date. CO2 utilization if possible is better, else we should focus on storage wherever possible. Storing CO2 will provide some time till CO2 utilization technologies, with exception of EOR becomes commercially available.

In this regards underground CO2?sequestration in sedimentary formations holds potential for considering. Underground CO2?sequestration is a mature technology and has been in use for over two decades globally and is currently storing about 3.7–4.2 MtCO2/year, for a cumulative total of 30.4 MtCO2?at the end of 2017

Captured CO2 when compressed, turns into a fluid almost as dense as water and can be pumped down into a porous geological formation, likewise for:

1.?????Deep saline formations which are sealed by a caprock for permanent storage. ??

2.?????Unmineable coal Seams located at great depth or too thin to be economically mined - Substantial quantity of Methane (CH4) can be extracted by injecting pressurized CO2 to the unmineable coal seams. CO2 has great affinity for coal and in general coal can store at least twice the amount of CO2 as methane on a molecular basis.?

CO2 is injected into coalbeds to exchange CO2 with methane. CO2 binds to the coal and is stored permanently. Depending on nature of Coal from Young immature Coals to Mature Anthracite, 1 ton of CO2 will push out CH4 to the extent to 1-10 times of CO2 injected.

3.?????Matured Oilfields - Injecting CO2 to increase oil production. EOR projects have been operating safely for decades and is well proven. As more CO2 is injected per unit of Oil recovered than CO2 emitted by burning of Oil, EOR is potential Carbon Negative cycle.

4.?????Unmineable Coal seams and Unviable / Depleted oil or gas fields with established trapping characteristics along with permeability to allow spread of injected CO2 in the seams.

5.?????Carbon mineralization of mafic and ultramafic rocks: Captured CO2 is injected in porous basaltic lava rocks - This technology is at early stages of implementation/ commercialization and further investigation is required. However, these rocks have potential of sequestering up to 60,000,000 GtCO2 and as sequestered CO2 forms carbonate, the probability of CO2 coming back to atmosphere is remote. However, as the case with every emerging technology, the resource needs to be economically accessible.

The cumulative release of anthropogenic carbon dioxide (CO2) into the atmosphere has been estimated at 2,035 ± 205 GtCO2?from 1870 to 2015 and today, emissions are about 40 GtCO2/yr. Mitigation of this CO2 will require sustained investment in the years to come and with proper Policy Support.

References:

1.?????Global CCS Institute, 2019.

2.?????IPCC Special Report, 2018.