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How faults control trap fill and migration pathways (view source)
Revision as of 14:06, 31 January 2014
, 14:06, 31 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 = Evaluating top and fault seal
| frompg = 10-1
| topg = 10-94
| author = Grant M. Skerlec
| link = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
A sealing fault can trap hydrocarbons but also will act as a barrier for hydrocarbon [[migration]] into traps beyond that fault. In addition, faults can act as baffles by deflecting hydrocarbons along [[migration pathways]] that may not be perpendicular to structural contours.
==Controlling trap fill==
Dry traps, or traps with limited fill, may exist because hydrocarbons have been trapped downdip along sealing faults. A fault can act as a barrier to (1) all hydrocarbons or (2) some of the hydrocarbons, allowing a limited volume to migrate. It can also act as a barrier along part of the fault plane and as a conduit along other parts of the fault plane.
==Controlling migration==
Where complex fault systems exist between a trap and a source kitchen or between two traps, migration pathways are correspondingly complex. Traps in this setting can have widely different migration/fill or charge risks, depending upon fault seal behavior.
==[[Migration]] parallel to faults==
Where the dip of carrier beds is not perpendicular to faults, even cross-leaking faults can act as barriers as long as the [[permeability]] of the carrier bed is higher than that of the fault. Hydrocarbons can then migrate parallel to a fault rather than across the fault, even though the fault cross-leaks. This baffle effect can direct hydrocarbons away from potential traps as well as toward others. [[Migration]] pathway maps are critical to prospect assessment.
==Example: Hudson field==
The Hudson field, North Sea, is an excellent example of how faults control migration pathways and charge.<ref name=ch10r36>Hardman, R., F., P., Booth, J., E., 1991, The significance of normal faults in the exploration and production of North Sea hydrocarbons, in Roberts, A., M., Yielding, G., Freeman, B., eds., The Geometry of Normal Faults: London, Geological Society of London, p. 1–16.</ref> The map and cross section in the following figure show that the first well, 210/24a-l, was located on the crest of an obvious structural high. This well encountered water-wet Brent Group sands. A second well on the flank, 210/24a-2, encountered oil shows suggestive of a local [[stratigraphic trap]]. Thirteen years after the initial well, the 210/24a-3 well discovered the Hudson field: a fault-dependent trap.
[[file:evaluating-top-and-fault-seal_fig10-30.png|thumb|{{figure number|10-30}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
The sealing fault trapped hydrocarbons in a flank fault compartment and prevented hydrocarbons from migrating into the more obvious structural high to the west. Predrill fault seal analysis and a migration pathway map would have correctly identified the sealing fault and would have placed a much greater risk on the success of the first well. In this case, new [[seismic data]] identified the sealing fault; however, numerous examples exist where the same error is made with high-quality seismic data. Hydrocarbons do not simply migrate into the crest of structural highs.
==Example: don field==
In the Don field, North Sea, sealing faults prevent hydrocarbons from migrating into fault compartments on the crest of a large structural high.<ref name=ch10r36 /> Instead, hydrocarbons are trapped in several fault compartments on the flank of the structure against cross-sealing faults that have sand/sand juxtapositions. Wells in three fault compartments (211/18-5, 10, and 16) in the crest of the structure are dry. Hydrocarbons have either been trapped downflank or have been deflected to the southwest by sealing faults.
[[file:evaluating-top-and-fault-seal_fig10-31.png|thumb|{{figure number|10-31}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
==See also==
* [[Fault seal and migration pathways]]
* [[How to construct migration pathway maps]]
* [[Effect of seal on hydrocarbon yield estimates]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.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:Evaluating top and fault seal]]
| 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 = Evaluating top and fault seal
| frompg = 10-1
| topg = 10-94
| author = Grant M. Skerlec
| link = http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=545
| isbn = 0-89181-602-X
}}
A sealing fault can trap hydrocarbons but also will act as a barrier for hydrocarbon [[migration]] into traps beyond that fault. In addition, faults can act as baffles by deflecting hydrocarbons along [[migration pathways]] that may not be perpendicular to structural contours.
==Controlling trap fill==
Dry traps, or traps with limited fill, may exist because hydrocarbons have been trapped downdip along sealing faults. A fault can act as a barrier to (1) all hydrocarbons or (2) some of the hydrocarbons, allowing a limited volume to migrate. It can also act as a barrier along part of the fault plane and as a conduit along other parts of the fault plane.
==Controlling migration==
Where complex fault systems exist between a trap and a source kitchen or between two traps, migration pathways are correspondingly complex. Traps in this setting can have widely different migration/fill or charge risks, depending upon fault seal behavior.
==[[Migration]] parallel to faults==
Where the dip of carrier beds is not perpendicular to faults, even cross-leaking faults can act as barriers as long as the [[permeability]] of the carrier bed is higher than that of the fault. Hydrocarbons can then migrate parallel to a fault rather than across the fault, even though the fault cross-leaks. This baffle effect can direct hydrocarbons away from potential traps as well as toward others. [[Migration]] pathway maps are critical to prospect assessment.
==Example: Hudson field==
The Hudson field, North Sea, is an excellent example of how faults control migration pathways and charge.<ref name=ch10r36>Hardman, R., F., P., Booth, J., E., 1991, The significance of normal faults in the exploration and production of North Sea hydrocarbons, in Roberts, A., M., Yielding, G., Freeman, B., eds., The Geometry of Normal Faults: London, Geological Society of London, p. 1–16.</ref> The map and cross section in the following figure show that the first well, 210/24a-l, was located on the crest of an obvious structural high. This well encountered water-wet Brent Group sands. A second well on the flank, 210/24a-2, encountered oil shows suggestive of a local [[stratigraphic trap]]. Thirteen years after the initial well, the 210/24a-3 well discovered the Hudson field: a fault-dependent trap.
[[file:evaluating-top-and-fault-seal_fig10-30.png|thumb|{{figure number|10-30}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
The sealing fault trapped hydrocarbons in a flank fault compartment and prevented hydrocarbons from migrating into the more obvious structural high to the west. Predrill fault seal analysis and a migration pathway map would have correctly identified the sealing fault and would have placed a much greater risk on the success of the first well. In this case, new [[seismic data]] identified the sealing fault; however, numerous examples exist where the same error is made with high-quality seismic data. Hydrocarbons do not simply migrate into the crest of structural highs.
==Example: don field==
In the Don field, North Sea, sealing faults prevent hydrocarbons from migrating into fault compartments on the crest of a large structural high.<ref name=ch10r36 /> Instead, hydrocarbons are trapped in several fault compartments on the flank of the structure against cross-sealing faults that have sand/sand juxtapositions. Wells in three fault compartments (211/18-5, 10, and 16) in the crest of the structure are dry. Hydrocarbons have either been trapped downflank or have been deflected to the southwest by sealing faults.
[[file:evaluating-top-and-fault-seal_fig10-31.png|thumb|{{figure number|10-31}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
==See also==
* [[Fault seal and migration pathways]]
* [[How to construct migration pathway maps]]
* [[Effect of seal on hydrocarbon yield estimates]]
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/beaumont/ch10/ch10.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:Evaluating top and fault seal]]