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Oil and gas reservoir: Difference between revisions

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<onlyinclude>An '''oil and gas reservoir''' is a formation of rock in which [[oil]] and [[natural gas]] has accumulated within. The oil and gas collect in the small, connected pore spaces of rock and are sealed below ground surface by an impermeable layer of rock.</onlyinclude><ref>ZionOil. (June 5, 2015). ''Oil Reservoir'' [Online]. Available: https://www.zionoil.com/updates/oil-formed-part-3-oil-reservoir/</ref> These reservoirs are ''not'' "puddles" or "lakes" of oil beneath the surface, as there are no vast open cavities that contain oil.  
[[Category: Rudi grade Ashley write]]  
[[File:reservoir.png|400px|framed|center|Figure 1. An oil and gas reservoir. The different components are: I. Seal rock II. Reservoir rock III. Source rock.<ref>Wikimedia Commons. (June 5, 2015). ''Structural Trap'' [Online]. Available: http://upload.wikimedia.org/wikipedia/commons/8/81/Structural_Trap_%28Anticlinal%29.svg</ref>]]
<onlyinclude>An '''oil and gas reservoir''' is a formation of rock in which [[oil]] and [[natural gas]] has accumulated. The oil and gas collected in small, connected pore spaces of rock and are trapped within the reservoir by adjacent and overlying, impermeable layers of rock.</onlyinclude><ref>ZionOil. (June 5, 2015). ''Oil Reservoir'' [Online]. Available: https://www.zionoil.com/updates/oil-formed-part-3-oil-reservoir/</ref> Typical reservoirs are ''not'' "pools" or "lakes" of oil beneath the surface, as there are no vast open cavities that contain oil. Oil and gas reservoirs can also be referred to as "hydrocarbon reservoirs".
[[File:Anticline Reservoir.jpg|400px|thumb|Figure 1. An anticline oil and gas reservoir.<ref>Source unknown. Please contact us if you know this image's source.</ref>]]


Reservoirs are made of rock known as '''reservoir rock''' - shown in Figure 1, part II - these are types of rocks that are accessible and contain considerable amounts of oil and gas. <ref>SEED. (June 5, 2015). ''The Making of Oil'' [Online]. Available:http://web.archive.org/web/20060427134445/http://www.seed.slb.com/en/scictr/watch/makingoi/birth/birth.htm</ref> In order to be a reservoir rock, it must be both [[porosity|porous]] and [[permeability|permeable]]. If both porous and permeable, there are small pockets within the rock where oil or gas can settle and small channels connecting these pockets to allow the oil or gas to flow out of this rock easily when drilled for.<ref name=geo>Stephen Marshak. (June 5, 2015). ''Earth: Portrait of a Planet'', 3rd ed. New York, NY, U.S.A:W.W. Norton & Company, 2008</ref> These spaces between grains can develop as the formation of rock occurs or afterwards, usually as a result of [[groundwater]] passing through the rock and dissolving some of the [[sediment]].
Conventional hydrocarbon reservoirs consist of three main parts: the source rock, the reservoir rock, and the cap rock (Figure 1). The source rock is the rock that contains the [[kerogen]] that the oil and gas forms from. The reservoir rock is the porous, permeable rock layer or layers that hold the oil and gas. The cap rock seals the top and sides so that the hydrocarbons are trapped in the reservoir, while water often seals the bottom.<ref>SEED. (June 5, 2015). ''The Making of Oil'' [Online]. Available: http://web.archive.org/web/20060427134445/http://www.seed.slb.com/en/scictr/watch/makingoi/birth/birth.htm</ref>


For a reservoir to exist, oil and [[gas]] from the source rock (the rock containing [[kerogen]]) - shown in Figure 1, part III -  must migrate into the [[reservoir]] rock, which takes millions of years. This migration occurs because oil and gas are less [[density|dense]] than [[water]]. This difference in density causes the oil and gas to rise towards the surface so that they are above groundwater with the gas settling above the oil because of their different densities.  Migration pathways - a set of well connected fractures - must exist for this rising to occur.<ref name=geo/>
For a reservoir to exist, oil and [[gas]] from the source rock must migrate into the [[reservoir]] rock, which takes millions of years. This migration occurs because oil and gas are less [[density|dense]] than [[water]]. This difference in density causes the oil and gas to rise towards the surface so that they are above groundwater with the gas settling above the oil because of its lighter densities.  Migration pathways - a set of well connected fractures - must exist for this rising to occur.<ref name=geo/>


Finally, there must be some rock preventing the oil and gas from escaping the reservoir rock that they can travel so easily through. For a reservoir to exist the oil and gas must be trapped underground so that they do not produce an oil seep. '''[[oil and gas traps|Traps]]''' create the top layer of the reservoir, preventing the [[fossil fuel|fossil fuels]] from exiting the reservoir rock. There are two main components to a trap: the '''seal rock''' and a '''proper arrangement'''. The seal rock - shown in Figure 1, part I - is the impermeable rock that lies above the reservoir rock, trapping the oil and gas in. Lastly, for a trap to exist there must be the proper arrangement of rocks in the reservoir to create a small, restricted area for the oil and gas to accumulate.<ref name=geo/>
Reservoir rocks need to be both [[porosity|porous]] and [[permeability|permeable]].  This means that there are small pockets of space within the rock where oil or gas can settle and small channels connecting these pockets to allow the oil or gas to flow out of this rock easily when it is drilled.<ref name=geo>Stephen Marshak. (June 5, 2015). ''Earth: Portrait of a Planet'', 3rd ed. New York, NY, U.S.A:W.W. Norton & Company, 2008</ref> These spaces between grains can develop as the formation of rock occurs or afterwards, usually as a result of [[groundwater]] passing through the rock and dissolving some of the cement between sediment grains.  


The rock formation must be formed or deformed in such a way to create a [[oil and gas traps|trap]] for the oil and gas. [[Anticline]]s are the most common formation shape for this to occur. Anticlines for a rough "A" shape, with the cap rock making the sides of the "A". The [[fossil fuel|fossil fuels]] accumulate in the peak of the "A" and the bottom is sealed (usually with water), preventing the oil and gas from seeping out and escaping. <ref name=geo/>
==For Further Reading==
*[[Gas]]
*[[Oil]]
*[[Source rock]]
*[[Cap rock]]
*[[Oil and gas traps]]
*Or explore a [[Special:Random|random page]]


==References==
==References==
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Latest revision as of 18:15, 4 January 2019

An oil and gas reservoir is a formation of rock in which oil and natural gas has accumulated. The oil and gas collected in small, connected pore spaces of rock and are trapped within the reservoir by adjacent and overlying, impermeable layers of rock.[1] Typical reservoirs are not "pools" or "lakes" of oil beneath the surface, as there are no vast open cavities that contain oil. Oil and gas reservoirs can also be referred to as "hydrocarbon reservoirs".

Figure 1. An anticline oil and gas reservoir.[2]

Conventional hydrocarbon reservoirs consist of three main parts: the source rock, the reservoir rock, and the cap rock (Figure 1). The source rock is the rock that contains the kerogen that the oil and gas forms from. The reservoir rock is the porous, permeable rock layer or layers that hold the oil and gas. The cap rock seals the top and sides so that the hydrocarbons are trapped in the reservoir, while water often seals the bottom.[3]

For a reservoir to exist, oil and gas from the source rock must migrate into the reservoir rock, which takes millions of years. This migration occurs because oil and gas are less dense than water. This difference in density causes the oil and gas to rise towards the surface so that they are above groundwater with the gas settling above the oil because of its lighter densities. Migration pathways - a set of well connected fractures - must exist for this rising to occur.[4]

Reservoir rocks need to be both porous and permeable. This means that there are small pockets of space within the rock where oil or gas can settle and small channels connecting these pockets to allow the oil or gas to flow out of this rock easily when it is drilled.[4] These spaces between grains can develop as the formation of rock occurs or afterwards, usually as a result of groundwater passing through the rock and dissolving some of the cement between sediment grains.

The rock formation must be formed or deformed in such a way to create a trap for the oil and gas. Anticlines are the most common formation shape for this to occur. Anticlines for a rough "A" shape, with the cap rock making the sides of the "A". The fossil fuels accumulate in the peak of the "A" and the bottom is sealed (usually with water), preventing the oil and gas from seeping out and escaping. [4]

For Further Reading

References

  1. ↑ ZionOil. (June 5, 2015). Oil Reservoir [Online]. Available: https://www.zionoil.com/updates/oil-formed-part-3-oil-reservoir/
  2. ↑ Source unknown. Please contact us if you know this image's source.
  3. ↑ SEED. (June 5, 2015). The Making of Oil [Online]. Available: http://web.archive.org/web/20060427134445/http://www.seed.slb.com/en/scictr/watch/makingoi/birth/birth.htm
  4. ↑ 4.0 4.1 4.2 Stephen Marshak. (June 5, 2015). Earth: Portrait of a Planet, 3rd ed. New York, NY, U.S.A:W.W. Norton & Company, 2008
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