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Intact membrane seal leakage (view source)
Revision as of 17:42, 21 January 2014
, 17:42, 21 January 2014Initial import
{{publication
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting preservation and destruction of accumulations
| frompg = 11-1
| topg = 11-30
| author = Alton A. Brown
| link = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
An intact membrane seal fails when the [[capillary pressure]] (created by the height of an underlying petroleum column) exceeds the seal capillary displacement pressure. This type of seal does not fracture during deformation.
==Ductility and capillary displacement pressure==
Fine-grained, water-wet ductile rocks will seal as long as the capillary pressure exerted on the seal (the difference between the water and the petroleum fluid pressure) is less than the capillary displacement pressure of the matrix [[porosity]] of the seal. Under these conditions, the relative [[permeability]] of the seal to petroleum is zero. The accumulation remains preserved until one of three things happens:
* The seal is ruptured or altered.
* The structure is spilled.
* The petroleum is altered.
Most old accumulations have seals of this type.
Claystones, salt, and sulfates (gypsum and anhydrite) make seals of this sort because they are ductile under most geological strain rates and confining pressures. Ductility is important; if fracturing occurs, oil can leak through the fractures without invading the matrix porosity.
Deeply buried claystones, salts, and anhydrite have capillary displacement pressures great enough to exceed the buoyancy pressure from any reasonable oil column height (hundreds to thousands of feet). Conversely, silty mudrocks, shallow-buried claystones, and argillaceous siltstones have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point.
==Predicting leakage==
The failure of intact membrane seals after charging is rare because the capillary displacement pressure of mudrock seals increases with compaction and burial. Intact seal failure usually results in failure to trap in the first place. Limitations on the height of the petroleum column due to intact membrane seal failure can be evaluated by laboratory capillary pressure tests<ref name=ch11r4>Berg, R., R., 1975, [[Capillary pressure]]s in stratigraphic traps: AAPG Bulletin, vol. 59, p. 939–956.</ref> in conjunction with estimates of in situ petroleum density.
==See also==
* [[Leakage]]
* [[Leakage mechanisms]]
* [[Fractured membrane seal leakage]]
* [[Hydrofractured seal leakage]]
* [[Micropermeable seal leakage]]
* [[Diffusive seal leakage]]
* [[Predicting overall seal failure]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting preservation and destruction of accumulations]]
| image = exploring-for-oil-and-gas-traps.png
| width = 120px
| series = Treatise in Petroleum Geology
| title = Exploring for Oil and Gas Traps
| part = Predicting the occurrence of oil and gas traps
| chapter = Predicting preservation and destruction of accumulations
| frompg = 11-1
| topg = 11-30
| author = Alton A. Brown
| link = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
An intact membrane seal fails when the [[capillary pressure]] (created by the height of an underlying petroleum column) exceeds the seal capillary displacement pressure. This type of seal does not fracture during deformation.
==Ductility and capillary displacement pressure==
Fine-grained, water-wet ductile rocks will seal as long as the capillary pressure exerted on the seal (the difference between the water and the petroleum fluid pressure) is less than the capillary displacement pressure of the matrix [[porosity]] of the seal. Under these conditions, the relative [[permeability]] of the seal to petroleum is zero. The accumulation remains preserved until one of three things happens:
* The seal is ruptured or altered.
* The structure is spilled.
* The petroleum is altered.
Most old accumulations have seals of this type.
Claystones, salt, and sulfates (gypsum and anhydrite) make seals of this sort because they are ductile under most geological strain rates and confining pressures. Ductility is important; if fracturing occurs, oil can leak through the fractures without invading the matrix porosity.
Deeply buried claystones, salts, and anhydrite have capillary displacement pressures great enough to exceed the buoyancy pressure from any reasonable oil column height (hundreds to thousands of feet). Conversely, silty mudrocks, shallow-buried claystones, and argillaceous siltstones have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point.
==Predicting leakage==
The failure of intact membrane seals after charging is rare because the capillary displacement pressure of mudrock seals increases with compaction and burial. Intact seal failure usually results in failure to trap in the first place. Limitations on the height of the petroleum column due to intact membrane seal failure can be evaluated by laboratory capillary pressure tests<ref name=ch11r4>Berg, R., R., 1975, [[Capillary pressure]]s in stratigraphic traps: AAPG Bulletin, vol. 59, p. 939–956.</ref> in conjunction with estimates of in situ petroleum density.
==See also==
* [[Leakage]]
* [[Leakage mechanisms]]
* [[Fractured membrane seal leakage]]
* [[Hydrofractured seal leakage]]
* [[Micropermeable seal leakage]]
* [[Diffusive seal leakage]]
* [[Predicting overall seal failure]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=545 Find the book in the AAPG Store]
[[Category:Predicting the occurrence of oil and gas traps]]
[[Category:Predicting preservation and destruction of accumulations]]