Changes

  | part    = Predicting the occurrence of oil and gas traps

  | part    = Predicting the occurrence of oil and gas traps

  | chapter = Evaluating top and fault seal

  | chapter = Evaluating top and fault seal

  | frompg  = 10-1

  | frompg  = 10-23

  | topg    = 10-94

  | topg    = 10-25

  | author  = Grant M. Skerlec

  | author  = Grant M. Skerlec

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm

  | isbn    = 0-89181-602-X

  | isbn    = 0-89181-602-X

}}

}}

Fault zones in siliciclastic sequences consist of various proportions of sand and shale. There is a relationship between seal behavior and the inferred sand-shale ratio of the fault zone. Sand-rich portions of the fault zone leak; shale-rich portions of the fault zone seal. Given the complex structure and composition of fault zones and the many factors that could affect a seal, it has been surprising to find such a simple relationship, basin after basin.

[[Fault]] zones in siliciclastic sequences consist of various proportions of [[sand]] and [[shale]]. There is a relationship between seal behavior and the inferred sand-shale ratio of the fault zone. Sand-rich portions of the fault zone leak; shale-rich portions of the fault zone seal. Given the complex structure and composition of fault zones and the many factors that could affect a seal, it has been surprising to find such a simple relationship, basin after basin.

==Example: smear gouge==

==Example: smear gouge==

[[file:evaluating-top-and-fault-seal_fig10-20.jpg|300px|thumb|{{figure number|1}}Smear gouge along a normal fault found in a sequence of Permian-Carboniferous sand and shales near Lynemouth, U.K..]]

[[file:evaluating-top-and-fault-seal_fig10-20.jpg|300px|thumb|{{figure number|1}}Smear gouge along a normal fault found in a sequence of Permian-Carboniferous sand and shales near Lynemouth, U.K..]]

[[:file:evaluating-top-and-fault-seal_fig10-20.jpg|Figure 1]] is an example of smear gouge along a normal fault found in a sequence of Permian-Carboniferous sand and shales near Lynemouth, U.K. Ductile, light gray shales have been incorporated in the fault zone as a continuous layer sourced from a bed in the footwall (upper left). Similarly, a bed of coal (black) in the footwall and sandstone in the hanging wall have been incorporated as discontinuous fragments in the fault zone. The coal, however, is intensely fractured, reflecting brittle rather than ductile deformation.

[[:file:evaluating-top-and-fault-seal_fig10-20.jpg|Figure 1]] is an example of smear gouge along a [[normal fault]] found in a sequence of [[Permian]]-[[Carboniferous]] sand and shales near Lynemouth, U.K. Ductile, light gray shales have been incorporated in the fault zone as a continuous layer sourced from a bed in the [[footwall]] (upper left). Similarly, a bed of [[coal]] (black) in the [[footwall]] and sandstone in the [[hanging wall]] have been incorporated as discontinuous fragments in the fault zone. The coal, however, is intensely fractured, reflecting [[Brittleness|brittle]] rather than [[Ductility|ductile]] [[deformation]].

Shale-rich gouge zones can create impermeable barriers. The following, a normal fault in Jurassic and Triassic sediments near Lilstock, U.K., shows a gouge zone approximately [[length::5 m]] thick. The gouge consists predominantly of ductile shales and marls as well as small amounts of brittle limestones. Faults with similar shale-rich gouge in producing fields create seals.

Shale-rich [[gouge zone]]s can create impermeable barriers. The following, a normal fault in [[Jurassic]] and [[Triassic]] sediments near Lilstock, U.K., shows a gouge zone approximately [[length::5 m]] thick. The gouge consists predominantly of ductile shales and marls as well as small amounts of brittle limestones. Faults with similar shale-rich gouge in producing fields create seals.

==Example: spectrum of gouge compositions==

==Example: spectrum of gouge compositions==

* [[Quantitative fault seal analysis]]

* [[Quantitative fault seal analysis]]

* [[Limitations of quantitative fault seal analysis]]

* [[Limitations of quantitative fault seal analysis]]

* [[Example of routine fault seal analysis: gulf coast]]

* [[Fault seal analysis example: Gulf Coast]]

==External links==

==External links==

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

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

[[Category:Evaluating top and fault seal]]

[[Category:Evaluating top and fault seal]]