Shale is traditionally regarded as a potential source rock and seal/cap rock for conventional hydrocarbon reservoirs. More recently, shale has been recognized as a potential reservoir for hydrocarbons, although with lower permeability and a larger content of organic matter than conventional reservoirs. A shale reservoir is differentiated from low permeability sandstones and carbonates on the basis of a higher content of organic matter and lower permeability. In a shale reservoir, gas typically occurs in two modes: adsorbed on organic matter within the shale bed, in a similar manner to coalbed methane, and as free gas in pores within the shale matrix, similar to conventional reservoirs. The low permeability of shale reservoirs dictates that specialized completion techniques are necessary to enable production, specifically hydraulic fracturing.

A summary report 'What is Shale Gas? An Introduction to Shale-Gas Geology in Alberta' is available on the AGS website. The report discusses relevant geological and geochemical criteria required for viable shale deposits, including the type, amount and maturation of organic matter within a shale bed, gas contents and permeability.

The report also describes a few of the older shale deposits in the United States from which hydrocarbons are being produced. The selection of shale deposits is discussed in terms of potential analogues for Alberta shale. Similarities and differences, with emphasis on geological, geochemical and mineralogical components are presented to highlight the potential hydrocarbon production from Alberta shale.

Exshaw Shale

Exshaw shale exposed at Jura Creek, Alberta

During 2012 an evaluation of shale hydrocarbon potential in 8 formations was published titled ‘Summary of Alberta's Shale- and Siltstone-Hosted Hydrocarbon Resource Potential’ to provide estimates of the amount of hydrocarbons contained in each formation. Five units show immediate potential: the Duvernay Formation, the Muskwa Formation, the Montney Formation, the Nordegg Member, and the basal Banff and Exshaw formations. The study also includes a preliminary assessment of the Colorado, Wilrich, Rierdon, and Bantry shale deposits.

The shale resource evaluation provides an understanding of the volume and distribution of shale hydrocarbon resources in Alberta and may be used to assist in the planning of resource allocation and conservation, commingling and rights assignment, royalty assessment, land and water usage, and environmental stewardship.

Duvernay Formation
Duvernay Formation shale.
Details about the map can be found in the 2012 report.