Unconventional Reservoirs

Conventional oil and gas resources are generally produced by vertical wells that target high porosity and permeability reservoir rocks and spatially defined hydrocarbon pools. Unconventional oil and gas resources are typically more challenging to extract due to being distributed throughout the pore spaces of very low porosity and permeability reservoir rocks. Because of technological advancements such as horizontal drilling and hydraulic fracturing, these previously uneconomical resources are the focus of new oil and gas exploration and development.

Unconventional resources that have contributed to Wyoming’s oil and gas industry include shale gas, tight gas and oil sands, shale oil, and coalbed natural gas. The 2011 through 2019 increase in Wyoming’s oil production can largely be attributed to the exploration and development of stacked unconventional reservoirs in the Powder River and Denver basins, such as the Teapot, Parkman, Sussex, Shannon, Turner, Wall Creek, Niobrara, and Codell.

Shale gas is natural gas locked in shale formations. In these reservoirs, the shale is both the source and the reservoir rock. An example of shale gas in Wyoming is the Hillard-Baxter system in the Greater Green River Basin.

Tight gas and oil reservoirs contain natural gas and oil trapped in the pores of siltstones and sandstones with very low permeability (<0.1 millidarcy) and very low porosity (<10%). The prolific Jonah, Pinedale, and Wamsutter fields are Wyoming’s largest tight gas reservoirs.

Shale oil is oil locked in shales and associated tight siltstones or carbonates, all of which have low permeability and porosity. Examples from Wyoming include the Niobrara Shale and Green River Formation. Note: shale oil should not be confused with oil shale. Oil shales are shales that contain kerogen. Generally, hydrocarbons cannot be produced from oil shale using wells. Mining or in-situ heating processes are necessary to extract and convert the kerogen.

Coalbed natural gas (CBNG), commonly called coalbed methane, is natural gas stored in coal beds. For more information, see the Coalbed Natural Gas tab on this page.

types of reservoirs
Schematic diagram showing different types of conventional and unconventional reservoirs. [Credit: WSGS]


Rachel Toner, rachel.toner@wyo.gov

Derek Lichtner, derek.lichtner@wyo.gov