1 Injecting Compressed CO pumped underground via well 2 Containment CO impermeable cap rock layer on top of the reservoir or aquifer prevents di usion to the ground 3 Trapping CO moves within store and becomes trapped by dissolving in brine or being physically absorbed in small rock pores 4 Plugging At the end of operation, a cement plug is used to seal the injection well permanently
Injection from onshore facilities
Injection from o shore facilities
Capture
Large-scale CO emission source
Pipeline transportation
Pipeline transportation
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4
1
Cap rock
1
1
2
Cap rock
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Cement plug
Minimum injection depth 800m
CO
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CO
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Onshore or o shore injection into saline aquifers or depleted oil/gas eld
Onshore aquifer
3
O shore aquifer
Figure 3 The process of storing CO 2 in onshore and offshore aquifers
Importance of the source of CO₂ The ultimate carbon balance of capturing, utilising, and storing CO₂ will depend on the source of CO₂ and the duration of its storage and/or utilisation. The capture of CO₂ from fossil fuel combustion or industrial processes can result in sector decarbonisation if the CO₂ is stored or used in long-term applications such as construction aggregates. It can increase carbon efficiency if CO₂ is used for short-term applications (for example, to produce a synthetic fuel product), but it will never result in net carbon removal. In contrast, if CO₂ is captured via photosynthesis or DAC and either stored or permanently used, it can generate net carbon removal. Any public policies that support CCUS, and all carbon accounting for CCUS, must therefore be based on a rigorous assessment of the carbon effect, combining both sources and end-of-life outcomes. Carbon storage can be safe and permanent with strict regulation Storage can be safe and permanent, provided it is well managed and strongly regulated. This is achieved through a series of manmade and natural factors, which act as barriers preventing leakage: • Artificial measures include plugging injection wells with steel and concrete seals; natural factors relate to CO₂ being injected under a
cap rock which acts as a barrier to release; over time, the CO₂ is dissolved in brine or physically absorbed into rock pores. • Although manmade storage sites have not been in operation long enough to prove their capacity to permanently trap CO₂, naturally occurring subterranean stores of CO₂ have remained trapped for thousands of years. This is further supported by real-world evidence from existing CCS facilities running since the 1990s and from academic studies of the technical feasibility. Theoretically, there is a risk that CO₂ injected underground may leak out of the reservoir through naturally occurring pathways (such as faults) or via manmade pathways (such as faulty wells). CO₂ leaks will only be minimised if strong regulation is enforced. Oil and gas companies have experience in drilling, pumping, simulation of geological behaviours, and well management, which means the expertise required to inject and store CO₂ underground is already available. Strong safety and regulatory regimes will need to be put in place to ensure the risk of accidental leaks is limited, with parties held accountable when managing large volumes of CO₂. Limited applications of carbon utilisation Utilisation of CO₂ is expected to account for around 35% of all captured CO₂ in 2050. Utilisation is typically justified under one of three cases:
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