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Line 22: − + − 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_fig10-31.png|thumb|{{figure number|10-31}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
How faults control trap fill and migration pathways (view source)
Revision as of 20:56, 10 February 2014
, 20:56, 10 February 2014no edit summary
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.
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==
==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. 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==
==Example: Hudson field==
[[file:evaluating-top-and-fault-seal_fig10-30.png|thumb|{{figure number|10-30}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
[[file:evaluating-top-and-fault-seal_fig10-30.png|thumb|{{figure number|1}}After .<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, 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 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 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|thumb|{{figure number|2}}After .<ref name=ch10r36 /> Copyright: Geological Society of London.]]
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.
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.
==See also==
==See also==