Hydrocarbon formation takes place in sedimentary basins. Sedimentary basins are caused by subsidence of the Earth’s crust. In an ocean setting, where oil and gas can form, this is usually caused by crustal thinning related to tectonic processes.
Crustal thinning leads to sagging which is then filled in with sediments, forming a sedimentary basin. (https://en.wikipedia.org/wiki/Santos_Basin, accessed 27/05/2020)
Subsidence of the crust allows it to sink downwards. This turns into a depression in which sediments can accumulate. If the sediments accumulating in the basin contain around 2% organic material, such as dead plants and plankton, then there is a chance that oil and gas can form.
- To learn more about Oil and Gas formation read: Oil Migration
Different geological settings can trap oil to form a reservoir. (https://commons.wikimedia.org/wiki/File:Oil_traps.svg, accessed 27/5/2020)
The hydrocarbons will migrate upwards through permeable rock until they reach the surface or a geological trap. A geological trap is caused by an impermeable barrier. Frequently this a rock type such as clay, where the sediment shape and size make it very difficult for fluid to pass through. Other impermeable barriers could include a salt dome.
- To read more about permeable and impermeable rocks with a corresponding tasty experiment read this blog post: Reservoir Rock
Geological traps are not only important for the discovery of oil and gas reservoirs but are also considered potential sites for carbon dioxide storage and even nuclear waste. They are generally stable areas with low potential for leakage, which could cause possible contamination.
- For more information on Carbon Capture and Storage read this blog post: Carbon Injection
- For activities relating to storing nuclear waste try this STEM project: Burying Nuclear Waste
- Have a go at creating your own sedimentary basin and geological traps following this activity: Sedimentary Basins with a corresponding video