What Are Deep Saline Aquifers?

Deep saline aquifers are subsurface rock formations — typically sandstones or carbonates — that contain water with high dissolved salt content (brine), unsuitable for drinking, agriculture, or industrial use. These formations sit thousands of feet below the surface, separated from useful groundwater by impermeable confining layers.

Saline aquifers are the primary target for permanent geologic CO2 sequestration because they offer enormous storage capacity, reliable confinement, and minimal interference with productive zones above.

Major U.S. Saline Aquifer Storage Targets

Mt. Simon Sandstone — Cambrian-age sandstone underlying the Illinois Basin (Illinois, Indiana, Kentucky); primary CCS target for Wabash Valley and other midwestern projects

Knox Group — Ordovician carbonates underlying the Mt. Simon

Salem Limestone — Mississippian carbonate; selectively used for storage in Illinois

Frio Formation — Gulf Coast Tertiary sandstone; Louisiana and East Texas CCS projects

Broom Creek Formation — North Dakota Permian sandstone; primary North Dakota Class VI storage

Madison Formation — Wyoming Mississippian carbonate; multiple Wyoming CCS projects

Mineral Rights vs Saline Aquifer Storage

Saline aquifers are typically not productive of oil or gas — they contain brine, not hydrocarbons. The legal question is who owns the void space (pore space) in the formation: the mineral owner or the surface owner?

Most U.S. states allocate pore space to the surface owner, particularly in jurisdictions with explicit statutory frameworks (Indiana, North Dakota, Wyoming). This means CCS lease payments and 45Q-related revenue typically go to the surface owner, not the mineral owner.

Mineral owners may still benefit indirectly: CCS projects must respect existing mineral rights and cannot interfere with current or reasonably anticipated future oil and gas operations. Mineral owner consent or non-objection may be required during Class VI permitting.