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Post-combustion carbon capture and storage separates carbon dioxide from an already formed flue gas, often by absorption in a regenerable solvent. The recovered gas must be purified, dehydrated, compressed, transported and injected into a suitable geological store. Caprock integrity, trapping mechanisms, monitoring and long-term liability matter as much as capture at the chimney.

Dilute carbon dioxide mixed with nitrogen requires a large gas-processing plant. Solvent regeneration consumes heat; compression consumes power; impurities can cause solvent degradation and corrosion. Retrofitting adds equipment, cooling demand and cost, and lowers net electrical output per unit fuel. Storage capacity, injection performance, leakage risk and public acceptance must be demonstrated, while upstream fuel-cycle emissions remain.

A capture fraction is not the same as the reduction per delivered kilowatt-hour. For illustrative capture $\chi =0.9$ and a plant-efficiency decrease from $0.4$ to $0.3$, residual stack emissions per delivered unit scale as $(1-\chi )(0.4/0.3)=0.133$, corresponding to an $86.7\%$ reduction rather than $90\%$. A full life-cycle assessment includes the additional fuel and upstream emissions. These figures illustrate the accounting and are not claimed as universal plant performance.

Recommend a three-dimensional multichannel seismic reflection survey, with enough areal aperture, offsets and repeated coverage to image the reservoir top, base, structure and possible leakage faults. A two-dimensional reconnaissance line can be cheaper but cannot map a three-dimensional closure reliably and is vulnerable to out-of-plane reflections. Use seismic migration to position dipping reflectors and faults; repeatable acquisition is desirable if later carbon capture and storage monitoring is intended.

A tuned marine marine air-gun array supplies broadband low-frequency seismic wave energy that can penetrate to $1.5\mathrm{km}$. Its trade-offs include bubble oscillations, seismic source ghosts, environmental constraints and limited high-frequency resolution. Sparker seismic source and boomer seismic source sources can provide higher-frequency, high-resolution shallow imaging, but commonly lack the energy and low frequencies needed to make them the first choice for this target. Source energy, bandwidth and repeatability must be balanced against penetration and vertical seismic resolution, approximately $V/(4f)$; at $V=2000\mathrm{m}{\mathrm{s}}^{-1}$ and $f=50\mathrm{Hz}$ this is about $10\mathrm{m}$. Required resolution ultimately depends on the unknown reservoir thickness.

A towed hydrophone streamer efficiently records pressure over many channels while a vessel moves. It primarily records P-wave pressure in the water, with flow noise, tow-depth ghosts, acquisition footprint and access restrictions as limitations. Seabed multicomponent nodes use hydrophones and geophones: pressure plus three-component ground motion can separate wavefields and recover converted S-wave information, and nodes permit wide azimuths and repeat surveys. Their costs include deployment, retrieval, coupling and positioning. Direct S waves do not propagate through the water column. The roughly $50\mathrm{m}$ water depth also creates a strong short-period water-layer seismic multiple that must be treated in processing.

An aquifer containing saline rather than fresh water. A deep saline aquifer can provide pore space for carbon capture and storage, but safe retention depends on reservoir connectivity, continuous caprock and pressure management.