Glossary

The process of geological sequestration consists of CO₂ capture from anthropogenic sources prior to its potential release into the atmosphere, and subsequent storage in geological media.

Acid Gas
A mixture of H₂S and CO₂. To bring produced sour gas to pipeline and market specifications, the acid gas needs to be removed from the gas stream. The acid gas component is usually removed by amine extraction processes and then injected into subsurface formations and/or desulphurized at surface.

Capture
The process of extracting CO₂ from a flue or waste gas stream that is the result of energy production or industrial activity.

Storage
The process of injecting CO₂ deep into geological formations for removal of CO₂ from the atmosphere and biosphere, and retention into the geosphere either permanently or for geologically significant periods of time.

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Sedimentary Basin
A geologically depressed area with thick sediments (sedimentary rocks) in the interior and thinner sediments at the edges. Sedimentary basins are commonly classified in terms of

• the type of crust on which the basin rests;
• the position of the basin with respect to plate margins; and
• the type of plate interactions occurring during sedimentation for basins lying close to a plate margin.

Source: Mitchell, A.H.C. and Reading, H.G. (1986): Sedimentation and tectonics; in Sedimentary environments and facies, 2nd ed., Blackwell, H.G. Reading (ed.), p. 471-519.

Western Canada Sedimentary Basin
The Western Canada Sedimentary Basin comprises the Alberta Basin and the Canadian part of the Williston Basin, the two being separated by the Sweetgrass/Bow Island Arch, which is a Precambrian structural high that crosses the Alberta-Saskatchewan border in the south. The Western Canada Sedimentary Basin is an interior basin and its general name is given to the wedge of sedimentary rocks that thickens westward from a zero-edge on the Canadian Shield to more than 6000 metres at the fold and thrust belt of the Rocky Mountains.

Source: Price, R.A. (1994): Cordilleran tectonics and the evolution of the Western Canada Sedimentary Basin; in Geologic Atlas of the Western Canada Sedimentary Basin; G.D. Mossop and I. Shetsen (comps.), Canadian Society of Petroleum Geologists and Alberta Research Council, p. 13-24.

Alberta Basin
The Alberta Basin constitutes the foreland basin of the Rocky Mountains and covers most of Alberta, northeastern British Columbia and southern Northwest Territories. The Alberta basin is separated from the Williston Basin by the Sweetgrass/Bow Island Arch.

Williston Basin
The Williston Basin is the archetypal intra-cratonic basin. The term 'Williston Basin' is generally applied to the sedimentary succession in Manitoba, Saskatchewan, the Dakotas and eastern Montana, but in a structural context it denotes an ellipsoidal depression centred in North Dakota. The basin is bordered to the east by the Sioux Arch of the Dakotas and southeastern Manitoba, and to the north by the Punnichy Arch fronting the Saskatchewan monocline. The western limit is the Sweetgrass/Bow Island Arch of northern Montana and southeastern Alberta that separates it from the Alberta Basin.

Source: Kent, D.M. and Christopher, J.E. (1994): Geological history of the Williston Basin and Sweetgrass Arch; in Geological Atlas of the Western Canada Sedimentary Basin, G. Mossop and I Shetsen (eds.), p. 421- 429.

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Stratigraphic Nomenclature

Group
Consists of assemblages of formations, but groups need to be composed entirely of named formations.

Formation
A body of rock, identified by lithic characteristics and stratigraphic position, that is usually but not necessarily tabular and is mappable on the Earth's surface and traceable in the subsurface. It must be of sufficient areal extent to be mappable at the scale of mapping commonly used in the region where it occurs.

Member
The formal lithostratigraphic unit next in rank below a formation and always part of a formation. A formation need not be divided entirely into members. A member may extend laterally from one formation to another.

Source: North American Commission on Stratigraphic Nomenclature (1983): North American Stratigraphic Code; American Association of Petroleum Geologists Bulletin, v. 67.

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Hydrostratigraphic Nomenclature

Aquifer
A layer, formation or group of formations of permeable rocks, saturated with water and with a degree of permeability that allows water to be withdrawn or injected. Sand and gravel layers, sandstone and carbonate strata usually form aquifers.

Source: de Marsily, G. (1986): Quantitative Hydrogeology; Academic Press, p. 115.

Aquitard
Less permeable beds, also saturated with water, from which water can't be produced through wells, but where the flow is significant enough to feed adjacent aquifers through vertical leakage. Till and shales form aquitards.

Source: de Marsily, G. (1986): Quantitative Hydrogeology; Academic Press, p. 131.

Aquiclude
Layers with very low permeability that can't give rise to any appreciable leakage. Examples of aquicludes are anhydrite and halite (salt) beds.

Source: de Marsily, G. (1986): Quantitative Hydrogeology; Academic Press, p. 131.

Reservoir
Permeable rock saturated with hydrocarbons (oil or gas) that can be produced through wells. Sandstone and carbonate rocks form reservoirs when saturated with oil and/or gas.

Cap Rock, Seal or Roof Rock
Less-permeable rock that confines reservoirs and prevents the migration or leakage of reservoir hydrocarbons. As the tendency of hydrocarbons in water-bearing rocks is to move upwards, the barrier rock normally lies above the reservoir rock and is called the roof rock, seal or cap rock. If the strata allow lateral movement of fluids, the lateral barrier may be called the wall rock or lateral seal. Shale, anhydrite and halite beds form reservoir cap rock.

Source: North, F.K. (1985): Petroleum Geology; Allen & Unwin (eds.); Boston, p. 607.