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Glossary

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1. Acquifer, see also under Deep Saline Formation

Aquifer:1) Aquifer means a subsurface layer or layers of rock or other geological strata of sufficient porosity and permeability to allow either a significant flow of groundwater or the abstraction of significant quantities of groundwater. 2) Layers of rock, sand or gravel that can absorb water and allow it to flow. An aquifer acts as a groundwater reservoir when the underlying rock is impermeable.

2. Brine

Brine: Any solution of water and salt (sodium chloride), usually containing other salts also. Ocean water contains 3% salt. Brines in underground formations can contain 20% salt or more. Brine must be desalinated before it can be used for drinking, and underground formations containing brines are not regarded as drinking water supplies.
 

3. Cap rock

Cap rock: Rock of very low permeability that acts as an upper seal to prevent fluid flow out of a reservoir.

4. Closure of a CO2 storage site

Closure of a storage site: means the definitive cessation of CO2 injection into that storage site.

5. CO2

Carbon dioxide (chemical formula CO2) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state. CO2 is a trace gas comprising 0.039% of the atmosphere.
As part of the carbon cycle known as photosynthesis, plants, algae, and cyanobacteria absorb carbon dioxide, sunlight, and water to produce carbohydrate energy for themselves and oxygen as a waste product. By contrast, during respiration they emit carbon dioxide, as do all other living things that depend either directly or indirectly on plants for food. Carbon dioxide is also generated as a by-product of combustion; emitted from volcanoes, hot springs, and geysers; and freed from carbonate rocks by dissolution.
 
 

6. CO2 plume

CO2 plume: means the dispersing volume of CO2 in the geological formation.

7. Containment

Containment: Restriction of movement of a fluid (such as supercritical CO2) to a specific place or space (like a storage aquifer or an oil or gas field in disuse).

8. Deep saline formation, see also under Aquifer

Deep saline formation or Saline Aquifer: rock formations that have their pore spaces filled with very salty water, exist in most regions of the world and appear to have a very large capacity for CO2 storage.

9. Demonstration plant

Demonstration plant: The demonstration plant (demo plant) is the scale-up between the pilot plant and the commercial concept that is to be developed. The main purpose of a demo plant is to validate the commercial ability of the technology.

10. Geologic formation

Geologic Formation: A contiguous underground material which is sufficiently homogeneous to be considered a single unit. Geologic formations with a certain structure and porosity present an opportunity for underground CO2 storage, as evidenced by existing formations which have been storing CO2 for millions of years. Examples of formations with CO2 sequestration potential include depleted oil reservoirs, depleted gas reservoirs, unmineable coal seams, saline formations, and shale formations.

11. Leakage

Leakage: refers to movement of fluids (including injected CO2) outside the injection formation. This can involve movement through the upper and lower bounding seals and through wellbore pathways. Leakage includes all pertinent pathways through the geosphere. Monitoring for leakage is important as it includes all processes leading to CO2 movement towards and possibly into the biosphere.

12. Migration of CO2

Migration of CO2: The movement of CO2 through a geologic formation, driven by density or a pressure differential.

13. Permeability

Permeability: The ability of a rock to transmit fluid through the pore spaces. A key influence on the rate of flow, movement and drainage of the fluids.

14. Pore space

Pore space:The spaces within a rock body that are unoccupied by solid material. Pore spaces include spaces between grains, fractures, vesicles, and voids formed by dissolution.

15. Reservoir

Reservoir: A subsurface, porous, permeable rock body surrounded by impermeable rock and containing oil, gas, or water. Most reservoir rocks consist individually or collectively of limestone, dolomites, or sandstone.

16. Sedimentary basin

Sedimentary basin: is a low area in the Earth’s crust, of tectonic origin, in which sediments accumulate. Continued deposition can cause further depression or subsidence.  Sedimentary basins range in size from as small as hundreds of meters to large parts of ocean basins. The essential element of the concept is tectonic creation of relief, to provide both a source of sediment and a relatively low place for the deposition of that sediment.  Sedimentary basins, or simply basins, vary from bowl-shaped to elongated troughs. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, hydrocarbon generation can occur within the basin.

17. Sedimentary basin

Sedimentary basin: is a low area in the Earth’s crust, of tectonic origin, in which sediments accumulate. Continued deposition can cause further depression or subsidence. Sedimentary basins range in size from as small as hundreds of meters to large parts of ocean basins. The essential element of the concept is tectonic creation of relief, to provide both a source of sediment and a relatively low place for the deposition of that sediment. Sedimentary basins, or simply basins, vary from bowl-shaped to elongated troughs. If rich hydrocarbon source rocks occur in combination with appropriate depth and duration of burial, hydrocarbon generation can occur within the basin.

18. Storage complex (EC)

Storage complex (EC): means the storage site and surrounding geological domain which can have an effect on overall storage integrity and security; that is, secondary containment formations.

19. Storage permit (EC)

Storage permit (EC): means a written and reasoned decision or decisions authorising the geological storage of CO2 in a storage site by the operator, and specifying the conditions under which it may take place, issued by the competent authority pursuant to the requirements of this Directive.

20. Storage site (EC)

Storage site (EC): A defined volume area within a geological formation used for the geological storage of CO2 and associated surface and injection facilities.

21. Supercritical CO2

Supercritical carbon dioxide: Supercritical CO2 means that the CO2 is processed to have a temperature and pressure that is above its thermodynamic critical point. This state means that CO2 can diffuse in solids like a gas and dissolve other materials like a liquid. This also means that density is compressed, thereby occupying a much smaller amount of space than it would in its natural state.

22. Water column

Water column (EC): means the vertically continuous mass of water from the surface to the bottom sediments of a water body.

23. Well

Well: Manmade hole drilled into the earth to produce liquids or gases, or to allow the injection of fluids.