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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.

A sealing fault can trap hydrocarbons but also will act as a barrier for hydrocarbon [[migration]] into [[trap]]s beyond that fault. In addition, faults can act as baffles by deflecting [[hydrocarbon]]s along [[migration pathways]] that may not be perpendicular to structural contours.

==Controlling trap fill==

==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.

[[Dry]] traps, or traps with limited fill, may exist because hydrocarbons have been trapped [[Dip|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==

==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 [[Calculating charge volume|charge]] risks, depending upon fault seal behavior.

Where complex fault systems exist between a [[trap]] and a [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil%20kitchen source kitchen] or between two traps, [[migration pathways]] are correspondingly complex. Traps in this setting can have widely different migration/fill or [[Calculating charge volume|charge]] risks, depending upon [[fault seal behavior]].

==Migration parallel to faults==

==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.

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. [[Hydrocarbon]]s 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 map construction|Migration pathway maps]] are critical to prospect assessment.

==Example: Hudson field==

==Example: Hudson field==

[[file:evaluating-top-and-fault-seal_fig10-30.png|300px|thumb|{{figure number|1}}Well located on the crest of an obvious structural high. After Hardman & Booth.<ref name=ch10r36 /> Copyright: Geological Society of London.]]

[[file:evaluating-top-and-fault-seal_fig10-30.png|300px|thumb|{{figure number|1}}Well located on the crest of an obvious structural high. After Hardman & Booth.<ref name=ch10r36 /> Copyright: Geological Society of London.]]

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, [http://sp.lyellcollection.org/content/56/1/1.abstract 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 [[:file:evaluating-top-and-fault-seal_fig10-30.png|Figure 1]] 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.

The Hudson field, North Sea, is an excellent example of how faults control [[migration pathways]] and [[Calculating charge volume|charge]].<ref name=ch10r36>Hardman, R., F., P., Booth, J., E., 1991, [http://sp.lyellcollection.org/content/56/1/1.abstract 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 [[:file:evaluating-top-and-fault-seal_fig10-30.png|Figure 1]] show that the first well, 210/24a-l, was located on the crest of an obvious structural high. This well encountered [http://www.glossary.oilfield.slb.com/en/Terms/w/water_wet.aspx water-wet] Brent Group sandstones. 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.

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.

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 construction|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==

==Example: Don field==

[[file:evaluating-top-and-fault-seal_fig10-31.png|300px|thumb|{{figure number|2}}Don Field, North Sea. After Hardman & Booth.<ref name=ch10r36 /> Copyright: Geological Society of London.]]

[[file:evaluating-top-and-fault-seal_fig10-31.png|300px|thumb|{{figure number|2}}Don Field, North Sea. After Hardman & Booth.<ref name=ch10r36 /> Copyright: Geological Society of London.]]

In the Don field, North Sea ([[:file:evaluating-top-and-fault-seal_fig10-31.png|Figure 2]]), 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.

In the Don field, North Sea ([[:file:evaluating-top-and-fault-seal_fig10-31.png|Figure 2]]), 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.

==See also==

==See also==