Natural gas, crude oil and coal are all fossil fuels formed from organic materials. Millions of years ago Saskatchewan was covered by a warm sea full of marine plants and animals. As the marine life died, organic plant and animal material built up under the sea bed. This material accumulated in layers along with sea shells, sand and mud. A sedimentary basin was formed as the sediments changed from sea shells to limestone, sand to sandstone and mud to shale. As the water receded, extreme heat and pressure caused by the build up of rock changed the plant and animal remains into crude oil and natural gas.
Crude oil and natural gas is found in sedimentary rock. Natural gas and crude oil are found in pools. They occur in small spaces or pores in sedimentary rock.
Sedimentary rock is very porous, or permeable. Hydrocarbons can move through the rock very easily because of its porosity. As the hydrocarbons move through the sedimentary rock they may come to a different type of rock, such as igneous or metamorphic rock. This rock is nonporous, or impermeable., and stops further movement of the hydrocarbons. A trap or reservoir is formed. There are two types of traps common in Saskatchewan:
Once a reservoir is formed, the natural movement of the earth may cause it to shift, allowing the crude oil and natural gas to move.
Natural gas and crude oil may occur alone or may be found together in the same rock formation. If natural gas and crude oil are together, natural gas is always found above the crude oil because it is lighter and "floats" above the crude oil. Salt water may also be found with hydrocarbon deposits.