Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Predicting preservation and destruction of accumulations

  | chapter = Predicting preservation and destruction of accumulations

  | frompg  = 11-1

  | frompg  = 11-15

  | topg    = 11-30

  | topg    = 11-15

  | author  = Alton A. Brown

  | author  = Alton A. Brown

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch11/ch11.htm

  | isbn    = 0-89181-602-X

  | 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]].

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==

==Ductility and capillary displacement pressure==

Most old accumulations have seals of this type.

Most old accumulations have seals of this type.

[[Claystone]]s, [[Halite|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.

[[Claystone]]s, [[Halite|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 [[Fracture|fracturing]] occurs, oil can leak through the [[fracture]]s 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 mudrock]]s, shallow-buried claystones, and [[argillaceous siltstone]]s have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point.

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 mudrock]]s, shallow-buried claystones, and [[argillaceous siltstone]]s have displacement pressures low enough to allow leakage even where the petroleum column has not filled to the structural spill point.

==Predicting leakage==

==Predicting leakage==

The failure of intact membrane seals after charging is rare because the capillary displacement pressure of mudrock seals increases with [[Reservoir_quality#Compaction|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 [[Capillary_pressure#Measuring_capillary_pressure|laboratory capillary pressure tests]]<ref name=ch11r4>Berg, R., R., 1975, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0059/0006/0900/0939.htm Capillary pressures in stratigraphic traps]: AAPG Bulletin, vol. 59, p. 939–956.</ref> in conjunction with estimates of in situ petroleum density.

The failure of intact membrane seals after [[Calculating charge volume|charging]] is rare because the capillary displacement pressure of mudrock seals increases with [[Reservoir_quality#Compaction|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 [[Capillary_pressure#Measuring_capillary_pressure|laboratory capillary pressure tests]]<ref name=ch11r4>Berg, R. R., 1975, [http://archives.datapages.com/data/bulletns/1974-76/data/pg/0059/0006/0900/0939.htm Capillary pressures in stratigraphic traps]: AAPG Bulletin, vol. 59, p. 939–956.</ref> in conjunction with estimates of in situ petroleum density.

==See also==

==See also==

* [[Micropermeable seal leakage]]

* [[Micropermeable seal leakage]]

* [[Diffusive seal leakage]]

* [[Diffusive seal leakage]]

* [[Predicting overall seal failure]]

* [[Seal failure prediction]]

==References==

==References==

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting the occurrence of oil and gas traps]]  

[[Category:Predicting preservation and destruction of accumulations]]

[[Category:Predicting preservation and destruction of accumulations]]