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Line 47: − − [[file:M91Ch13FG84.JPG|thumb|300px|{{figure number|6}}This faulted top reservoir map from the Staffa field in the UK North Sea is represented by a contoured surface and fault polygons. The fault polygons show the hanging wall and footwall fault cuts for the interpreted surface. The downthrown (hanging wall) side of the fault is indicated by a blocked out symbol (from Gluyas and Underhill).<ref name=Gluyasandunderhill_2003>Gluyas, J. G., and J. R. Underhill, 2003, The Staffa field, Block 3/8b, UK North Sea, in J. G. Gluyas and H. M. Hichens, eds., United Kingdom oil and gas fields, commemorative millennium volume: Geological Society (London) Memoir 20, p. 327–333.</ref> Reprinted with permission from the Geological Society.]] Line 59:
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Line 76: − − [[file:M91Ch13FG87.JPG|thumb|300px|{{figure number|9}}Fault damage zone from Moab, Utah. The outcrop is about 15 m (49 ft) high (photo courtesy of Angus MacLellan).]] Line 87:
Line 86: + + + + + − − [[file:M91Ch13FG88.JPG|thumb|300px|{{figure number|10}}Deformation bands in the Aztec Sandstone, Valley of Fire, Nevada. Increased compaction compared to the undeformed rock causes the deformation bands to be more resistant to weathering and to stand out as ridges. Individual bands are approximately planar, showing distinct tips even where they are closely spaced (bottom left photo). Porosity loss resulting from granular rearrangement and clay accumulation in the bands results in lowered permeability (bottom right photo). DB = deformation band (from Sternlof et al.<ref name=Sternlofetal_2004>Sternlof, K. R., J. R. Chapin, D. D. Pollard, and L. J. Durlofsky, 2004, [http://archives.datapages.com/data/bulletns/2004/09sep/1315/1315.HTM Permeability effects of deformation band arrays in sandstone]: AAPG Bulletin, v. 88, no. 9, p. 1315–1329.</ref>).]]
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A fault-repeated section is sometimes seen in a well ([[:file:M91Ch13FG82.JPG|Figure 4]]). Near-vertical or gently dipping wells cutting reverse faults will show a repeated pattern. A repeat section can also occur where a highly deviated well cuts through a normal fault at a shallower angle than the dip of the fault plane ([[:file:M91Ch13FG82.JPG|Figure 4]]).<ref name=Mulvany_1992>Mulvany, P. S., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0006/0000/0895.htm A model for classifying and interpreting logs of boreholes that intersect faults in stratified rocks]: AAPG Bulletin, v. 76, no. 6, p. 895–903.</ref>
A fault-repeated section is sometimes seen in a well ([[:file:M91Ch13FG82.JPG|Figure 4]]). Near-vertical or gently dipping wells cutting reverse faults will show a repeated pattern. A repeat section can also occur where a highly deviated well cuts through a normal fault at a shallower angle than the dip of the fault plane ([[:file:M91Ch13FG82.JPG|Figure 4]]).<ref name=Mulvany_1992>Mulvany, P. S., 1992, [http://archives.datapages.com/data/bulletns/1992-93/data/pg/0076/0006/0000/0895.htm A model for classifying and interpreting logs of boreholes that intersect faults in stratified rocks]: AAPG Bulletin, v. 76, no. 6, p. 895–903.</ref>
==Well tests and faults==
==Well tests and faults==
==Mapping faults==
==Mapping faults==
[[file:M91Ch13FG84.JPG|thumb|300px|{{figure number|6}}This faulted top reservoir map from the Staffa field in the UK North Sea is represented by a contoured surface and fault polygons. The fault polygons show the hanging wall and footwall fault cuts for the interpreted surface. The downthrown (hanging wall) side of the fault is indicated by a blocked out symbol (from Gluyas and Underhill).<ref name=Gluyasandunderhill_2003>Gluyas, J. G., and J. R. Underhill, 2003, The Staffa field, Block 3/8b, UK North Sea, in J. G. Gluyas and H. M. Hichens, eds., United Kingdom oil and gas fields, commemorative millennium volume: Geological Society (London) Memoir 20, p. 327–333.</ref> Reprinted with permission from the Geological Society.]]
Structure maps show the contoured depth surface and a representation of any faults cutting the surface. The faults are drawn as fault polygons marking the hanging wall and footwall fault cuts for the interpreted surface. The hanging wall is the rock volume above the fault plane, and the footwall is the rock volume that lies beneath it ([[:file:M91Ch13FG81.JPG|Figure 3]], [[:file:M91Ch13FG82.JPG|Figure 4]], [[:file:M91Ch13FG84.JPG|Figure 6]]).
Structure maps show the contoured depth surface and a representation of any faults cutting the surface. The faults are drawn as fault polygons marking the hanging wall and footwall fault cuts for the interpreted surface. The hanging wall is the rock volume above the fault plane, and the footwall is the rock volume that lies beneath it ([[:file:M91Ch13FG81.JPG|Figure 3]], [[:file:M91Ch13FG82.JPG|Figure 4]], [[:file:M91Ch13FG84.JPG|Figure 6]]).
Fault restoration can also give insights into the structural history of an oil field. By determining the timing for episodes of faulting, uplift, and erosion, insights can be gained that allow the structural controls on reservoir development to be understood.
Fault restoration can also give insights into the structural history of an oil field. By determining the timing for episodes of faulting, uplift, and erosion, insights can be gained that allow the structural controls on reservoir development to be understood.
==Fault geometries, linked faults, and relay ramps==
==Fault geometries, linked faults, and relay ramps==
==Fault damage zone==
==Fault damage zone==
<gallery mode=packed heights=300px widths=300px>
M91Ch13FG87.JPG|{{figure number|9}}Fault damage zone from Moab, Utah. The outcrop is about 15 m (49 ft) high (photo courtesy of Angus MacLellan).
M91Ch13FG88.JPG|{{figure number|10}}Deformation bands in the Aztec Sandstone, Valley of Fire, Nevada. Increased compaction compared to the undeformed rock causes the deformation bands to be more resistant to weathering and to stand out as ridges. Individual bands are approximately planar, showing distinct tips even where they are closely spaced (bottom left photo). Porosity loss resulting from granular rearrangement and clay accumulation in the bands results in lowered permeability (bottom right photo). DB = deformation band (from Sternlof et al.<ref name=Sternlofetal_2004>Sternlof, K. R., J. R. Chapin, D. D. Pollard, and L. J. Durlofsky, 2004, [http://archives.datapages.com/data/bulletns/2004/09sep/1315/1315.HTM Permeability effects of deformation band arrays in sandstone]: AAPG Bulletin, v. 88, no. 9, p. 1315–1329.</ref>).
</gallery>
A large number of fractures, microfaults, and deformation bands can be found in a zone (up to 100 m [328 ft] or more wide) on either side of major fault planes.<ref name=Aydinandjohnson_1978>Aydin, A., and A. M. Johnson, 1978, Development of faults as zones of deformation bands and as slip surfaces in sandstones: Pure and Applied Geophysics, v. 116, p. 931–942.</ref> <ref name=Jamisonandstearns_1982>Jamison, W. R., and D. W. Stearns, 1982, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0012/2550/2584.htm Tectonic deformation of Wingate Sandstone, Colorado National Monument]: AAPG Bulletin, v. 66, no. 12, p. 2584–2608.</ref> <ref name=Antonelliniandaydin_1995>Antonellini, M., and A. Aydin, 1995, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0079/0005/0600/0642.htm Effects of faulting on fluid flow in porous sandstones: Geometry and spatial distribution]: AAPG Bulletin, v. 79, no. 5, p. 642–670.</ref> These damage zones can be observed in outcrops and in cores from wells near large faults ([[:file:M91Ch13FG87.JPG|Figure 9]]).
A large number of fractures, microfaults, and deformation bands can be found in a zone (up to 100 m [328 ft] or more wide) on either side of major fault planes.<ref name=Aydinandjohnson_1978>Aydin, A., and A. M. Johnson, 1978, Development of faults as zones of deformation bands and as slip surfaces in sandstones: Pure and Applied Geophysics, v. 116, p. 931–942.</ref> <ref name=Jamisonandstearns_1982>Jamison, W. R., and D. W. Stearns, 1982, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0012/2550/2584.htm Tectonic deformation of Wingate Sandstone, Colorado National Monument]: AAPG Bulletin, v. 66, no. 12, p. 2584–2608.</ref> <ref name=Antonelliniandaydin_1995>Antonellini, M., and A. Aydin, 1995, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0079/0005/0600/0642.htm Effects of faulting on fluid flow in porous sandstones: Geometry and spatial distribution]: AAPG Bulletin, v. 79, no. 5, p. 642–670.</ref> These damage zones can be observed in outcrops and in cores from wells near large faults ([[:file:M91Ch13FG87.JPG|Figure 9]]).
Clean, porous sandstones respond to localized strain by forming deformation bands ([[:file:M91Ch13FG88.JPG|Figure 10]]). These are tabular zones where the grains are reorganized by grain sliding, rotation, and commonly fracturing in response to deformation processes including dilation, shearing, and compaction.<ref name=Fossenetal_2007>Fossen, H., R. A. Schultz, Z. K. Shipton, and K. Mair, 2007, Deformation bands in sandstone: A review: Journal of the Geological Society (London), v. 164, p. 755–769.</ref> Deformation bands are frequently sheared with shear offsets on a millimeter to centimeter scale. By comparison to open fractures, which tend to enhance permeability, deformation bands have a much reduced permeability compared to the undeformed host sandstone.<ref name=Antonelliniandaydin_1994>Antonellini, M., and A. Aydin, 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0003/0350/0355.htm Effect of faulting on fluid flow in porous sandstones: Petrophysical properties]: AAPG Bulletin, v. 78, no. 3, p. 355–377.</ref> Given that a damage zone can contain hundreds of deformation bands, then it is clear that even sand-sand contact faults with damage zones can have significantly reduced permeability across them.
Clean, porous sandstones respond to localized strain by forming deformation bands ([[:file:M91Ch13FG88.JPG|Figure 10]]). These are tabular zones where the grains are reorganized by grain sliding, rotation, and commonly fracturing in response to deformation processes including dilation, shearing, and compaction.<ref name=Fossenetal_2007>Fossen, H., R. A. Schultz, Z. K. Shipton, and K. Mair, 2007, Deformation bands in sandstone: A review: Journal of the Geological Society (London), v. 164, p. 755–769.</ref> Deformation bands are frequently sheared with shear offsets on a millimeter to centimeter scale. By comparison to open fractures, which tend to enhance permeability, deformation bands have a much reduced permeability compared to the undeformed host sandstone.<ref name=Antonelliniandaydin_1994>Antonellini, M., and A. Aydin, 1994, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0078/0003/0350/0355.htm Effect of faulting on fluid flow in porous sandstones: Petrophysical properties]: AAPG Bulletin, v. 78, no. 3, p. 355–377.</ref> Given that a damage zone can contain hundreds of deformation bands, then it is clear that even sand-sand contact faults with damage zones can have significantly reduced permeability across them.