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[[File:M91FG191.JPG|thumb|300px|{{figure number|1}}The photograph shows a shoreface profile on St. Cyrus Beach, Scotland. The beach is just over a hundred meters wide. Reservoir properties are influenced by the degree of wave reworking up the shoreface profile. Lower figure from McCubbin.<ref name=McCubbin>McCubbin, D. G., 1992, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0800/0809.htm Barrier Islands, strand-plains], in P. A. Scholle and D. R. Spearing, eds., Sandstone depositional environments: [http://store.aapg.org/detail.aspx?id=627 AAPG Memoir 31], p. 247–279.</ref> Reprinted with permission from the AAPG.]]

[[File:M91FG191.JPG|thumb|300px|{{figure number|1}}The photograph shows a shoreface profile on St. Cyrus Beach, Scotland. The beach is just over a hundred meters wide. Reservoir properties are influenced by the degree of wave reworking up the shoreface profile. Lower figure from McCubbin.<ref name=McCubbin>McCubbin, D. G., 1992, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0800/0809.htm Barrier Islands, strand-plains], in P. A. Scholle and D. R. Spearing, eds., Sandstone depositional environments: [http://store.aapg.org/detail.aspx?id=627 AAPG Memoir 31], p. 247–279.</ref>]]

Shoreface sands are deposited along shorelines, and they generally form extensive, high-quality reservoir systems ([[:File:M91FG191.JPG|Figure 1]]). Wave action and occasional storms act to deposit sand along the shoreface. The lower shoreface lies below fair-weather wave base but can be affected by storms; the sands tend to be siltier and more poorly sorted by comparison to the upper shoreface, where the sands have been subjected to wave winnowing. A shoreface deposit separated by a lagoon from the land is known as a barrier island.

Shoreface sands are deposited along shorelines, and they generally form extensive, high-quality reservoir systems ([[:File:M91FG191.JPG|Figure 1]]). Wave action and occasional storms act to deposit sand along the shoreface. The lower shoreface lies below fair-weather wave base but can be affected by storms; the sands tend to be siltier and more poorly sorted by comparison to the upper shoreface, where the sands have been subjected to wave winnowing. A shoreface deposit separated by a lagoon from the land is known as a barrier island.

==Shoreface sands form layer-cake geometries==

==Shoreface sands form layer-cake geometries==

Shoreface sands prograde by lateral accretion with a tendency to produce layer-cake tabular geometries. Depositional dead ends are rare within individual shoreface sandstones, and sweep efficiencies are generally high as a result; for example, Tyler and Ambrose<ref name=TA1986>Tyler, N., and W. A. Ambrose, 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0800/0809.htm Facies architecture and production characteristics of strand-plain reservoirs in North Markham-North Bay City field, Frio Formation, Texas]: AAPG Bulletin, v. 70, no. 7, p. 809–829.</ref> described excellent continuity and efficient simple sweep in the Carlson shoreface reservoir of the North Markham-North City Bay field of Texas. The large size and excellent lateral continuity of shoreface reservoirs give a reasonable chance that these systems will be in contact with an aquifer (Table 1):

Shoreface sands prograde by [[lateral]] accretion with a tendency to produce layer-cake tabular geometries. Depositional dead ends are rare within individual shoreface sandstones, and sweep efficiencies are generally high as a result; for example, Tyler and Ambrose<ref name=TA1986>Tyler, N., and W. A. Ambrose, 1986, [http://archives.datapages.com/data/bulletns/1986-87/data/pg/0070/0007/0800/0809.htm Facies architecture and production characteristics of strand-plain reservoirs in North Markham-North Bay City field, Frio Formation, Texas]: AAPG Bulletin, v. 70, no. 7, p. 809–829.</ref> described excellent continuity and efficient simple sweep in the Carlson shoreface reservoir of the North Markham-North City Bay field of Texas. The large size and excellent lateral continuity of shoreface reservoirs give a reasonable chance that these systems will be in contact with an aquifer (Table 1):

{| class="wikitable"

{| class="wikitable"

| Common tidal and fluvial channel fills ||  || Permeability contrast with shore face or barrier island sandstones can result in bypassed oil

| Common tidal and fluvial channel fills ||  || Permeability contrast with shore face or barrier island sandstones can result in bypassed oil

|-

|-

| Lagoonal sandstone bodies (washover fans and flood-tidal deltas) can be wholly or partially enclosed in mudstone ||  || Can form discrete hydraulic units or compartments with bypassed oil

| Lagoonal sandstone bodies (washover fans and flood-tidal deltas) can be wholly or partially enclosed in [[mudstone]] ||  || Can form discrete hydraulic units or compartments with bypassed oil

|}

|}

==Parasequences and parasequence sets==

==Parasequences and parasequence sets==

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M91Ch11FG73.JPG|{{figure number|2}}Lithofacies map for the upper Piper Sand interval of the Scott field, UK North Sea (from Guscott et al.<ref name=Guscott>Guscott, S., K. Russell, A. Thickpenny, and R. Poddubiuk, 2003, The Scott field, Blocks 15/21a, 15/22, 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. 467–481.</ref>). Reprinted with permission from the Geological Society. See also [[Lithofacies maps]]<ref>Shepherd, M., 2009, [http://archives.datapages.com/data/specpubs/memoir91/CHAPTER11/CHAPTER11.HTM Lithofacies maps], in M. Shepherd, Oil field production geology: [http://store.aapg.org/detail.aspx?id=788 AAPG Memoir 91], p. 93-98.

M91Ch11FG73.JPG|{{figure number|2}}[[Lithofacies map]] for the upper Piper Sand interval of the Scott field, UK North Sea (from Guscott et al.<ref name=Guscott>Guscott, S., K. Russell, A. Thickpenny, and R. Poddubiuk, 2003, The Scott field, Blocks 15/21a, 15/22, 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. 467–481.</ref>). Reprinted with permission from, and &copy; by, the Geological Society. See also Lithofacies maps<ref>Shepherd, M., 2009, [http://archives.datapages.com/data/specpubs/memoir91/CHAPTER11/CHAPTER11.HTM Lithofacies maps], in M. Shepherd, Oil field production geology: [http://store.aapg.org/detail.aspx?id=788 AAPG Memoir 91], p. 93-98.

M91FG102.JPG|{{figure number|3}}Vertical flow barriers can control the drainage patterns in a reservoir. The degree to which individual barriers are effective across the reservoir can be characterized by vertical flow barrier maps.

M91FG102.JPG|{{figure number|3}}Vertical flow barriers can control the drainage patterns in a reservoir. The degree to which individual barriers are effective across the reservoir can be characterized by vertical flow barrier maps.

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M91Ch6FG42.JPG|{{figure number|4}}Example of a sedimentological core log, Well d-2-C/94a-16, Peejay field, Canada (after Caplan and Moslow).<ref>Caplan, M. L., and T. F. Moslow, 1999, [http://archives.datapages.com/data/bulletns/1999/01jan/0128/0128.htm Depositional origin and facies variability of a Middle Triassic barrier island complex, Peejay field, northeastern British Columbia]: AAPG Bulletin, v. 83, no. 1, p. 128–154.</ref> From Shepherd.<ref>Shepherd, M., 2009, [http://archives.datapages.com/data/specpubs/memoir91/CHAPTER06/CHAPTER06.HTM Sources of data], in M. Shepherd, Oil field production geology: [http://store.aapg.org/detail.aspx?id=788 AAPG Memoir 91], p. 49-63.

M91Ch6FG42.JPG|{{figure number|4}}Example of a sedimentological core log, Well d-2-C/94a-16, Peejay field, Canada (after Caplan and Moslow).<ref>Caplan, M. L., and T. F. Moslow, 1999, [http://archives.datapages.com/data/bulletns/1999/01jan/0128/0128.htm Depositional origin and facies variability of a Middle Triassic barrier island complex, Peejay field, northeastern British Columbia]: AAPG Bulletin, v. 83, no. 1, p. 128–154.</ref> From Shepherd.<ref>Shepherd, M., 2009, [http://archives.datapages.com/data/specpubs/memoir91/CHAPTER06/CHAPTER06.HTM Sources of data], in M. Shepherd, Oil field production geology: [http://store.aapg.org/detail.aspx?id=788 AAPG Memoir 91], p. 49-63.

M91FG108.JPG|{{figure number|5}}The barrier bar-shoreface interval of the Brent Group reservoir in the Thistle field, UK North Sea, shows an upward-increasing permeability profile. This pattern is favorable to a high sweep efficiency (from Williams and Milne).<ref>Williams, R. R., and A. D. Milne, 1991, The Thistle field, Blocks 211/18a and 211/19, UK North Sea, in I. L. Abbots, ed., United Kingdom oil and gas fields, 25 years commemorative volume: Geological Society (London) Memoir 14, p. 199–207.</ref> Reprinted with permission from the Geological Society.

M91FG108.JPG|{{figure number|5}}The barrier bar-shoreface interval of the Brent Group reservoir in the Thistle field, UK North Sea, shows an upward-increasing permeability profile. This pattern is favorable to a high sweep efficiency (from Williams and Milne).<ref>Williams, R. R., and A. D. Milne, 1991, The Thistle field, Blocks 211/18a and 211/19, UK North Sea, in I. L. Abbots, ed., United Kingdom oil and gas fields, 25 years commemorative volume: Geological Society (London) Memoir 14, p. 199–207.</ref> Reprinted with permission from, and &copy; by, the Geological Society.

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Shoreface sandstones characteristically show upward-increasing permeability profiles. This in turn reflects increasing grain size and better sorting higher up the shoreface profile (see also [[:File:M91Ch6FG42.JPG|Figures 4]] and [[:File:M91FG108.JPG|5]]). A contrast in rock properties is characteristically seen between the lower and upper shoreface intervals. Upper shoreface beach facies associations generally show higher permeabilities than lower shoreface sediments. When a shoreface sand is subjected to a waterflood, the water tends to edge ahead through the high-permeability tops of these cycles by viscous forces. Gravity and capillary action will then draw the water down through the shoreface cycle into the lower units, displacing oil upward. Sweep efficiencies can be high as a result.

Shoreface sandstones characteristically show upward-increasing permeability profiles. This in turn reflects increasing [[grain size]] and better sorting higher up the shoreface profile (see also [[:File:M91Ch6FG42.JPG|Figures 4]] and [[:File:M91FG108.JPG|5]]). A contrast in rock properties is characteristically seen between the lower and upper shoreface intervals. Upper shoreface beach facies associations generally show higher permeabilities than lower shoreface sediments. When a shoreface sand is subjected to a waterflood, the water tends to edge ahead through the high-permeability tops of these cycles by viscous forces. [[Gravity]] and capillary action will then draw the water down through the shoreface cycle into the lower units, displacing oil upward. Sweep efficiencies can be high as a result.

The degree to which the lower part of the shoreface is swept by water will depend on the magnitude of the vertical permeability within the lower shoreface. In the Middle Jurassic Brent Province of the UK North Sea, bypassed oil is often found within the lower shoreface facies association (Rannoch Formation). The overlying upper shoreface (Etive Formation) is typically an interval of water overrun.<ref>Thomas, J. M. D., and R. Bibby, 1991, The depletion of the Rannoch-Etive sand unit in Brent sands reservoirs in the North Sea, in W. Linville, ed., Reservoir characterization III: Tulsa, PennWell Books, 1008 p.</ref> This behavior can be reinforced by a zone of mica concentration at the top of the lower shoreface, which acts as a baffle to vertical flow (Wetzelaer et al., 1996). Horizontal wells have been drilled in several Brent Province fields to target bypassed oil in the lower shore face.<ref>Braithwaite, C. I. M., J. D. Marshall, and T. C. Holland, 1989, Improving recovery from the Dunlin field, U.K. northern North Sea: Presented at the 54th Annual Technical Conference of the Society of Petroleum Engineers, San Antonio, Texas, SPE Paper 19878, 18 p.</ref><ref>Black, R. C., H. J. Poelen, M. J. Roberts, and S. E. Roddy, 1999, Tern field development: A marriage of new technologies for business benefit, in A. J. Fleet and S. A. R. Boldy, eds., Petroleum geology of northwest Europe: Proceedings of the 5th Conference, Geological Society (London), p. 1063–1073.</ref> The success of these wells depends on the presence of low vertical permeabilities at the top of the lower shoreface interval in order to prevent water coning down from the swept upper shoreface interval.

The degree to which the lower part of the shoreface is swept by water will depend on the magnitude of the vertical permeability within the lower shoreface. In the Middle Jurassic Brent Province of the UK North Sea, bypassed oil is often found within the lower shoreface facies association (Rannoch Formation). The overlying upper shoreface (Etive Formation) is typically an interval of water overrun.<ref>Thomas, J. M. D., and R. Bibby, 1991, The depletion of the Rannoch-Etive sand unit in Brent sands reservoirs in the North Sea, in W. Linville, ed., Reservoir characterization III: Tulsa, PennWell Books, 1008 p.</ref> This behavior can be reinforced by a zone of mica concentration at the top of the lower shoreface, which acts as a baffle to vertical flow (Wetzelaer et al., 1996). Horizontal wells have been drilled in several Brent Province fields to target bypassed oil in the lower shore face.<ref>Braithwaite, C. I. M., J. D. Marshall, and T. C. Holland, 1989, Improving recovery from the Dunlin field, U.K. northern North Sea: Presented at the 54th Annual Technical Conference of the Society of Petroleum Engineers, San Antonio, Texas, SPE Paper 19878, 18 p.</ref><ref>Black, R. C., H. J. Poelen, M. J. Roberts, and S. E. Roddy, 1999, Tern field development: A marriage of new technologies for business benefit, in A. J. Fleet and S. A. R. Boldy, eds., Petroleum geology of northwest Europe: Proceedings of the 5th Conference, Geological Society (London), p. 1063–1073.</ref> The success of these wells depends on the presence of low vertical permeabilities at the top of the lower shoreface interval in order to prevent water coning down from the swept upper shoreface interval.

==Beach sandstones==

==Beach sandstones==

[[File:M91FG117.JPG|thumb|300px|{{figure number|6}}Time series of water cut maps from the West Cornelius reservoir, North Markham-North Bay City field, Texas. In this strand-plain reservoir, east-northeastndashwest-southwest-oriented beach ridge macroforms are fairways for water ingress. Tidal mud flat deposits south of the field restrict water influx from this direction (from Tyler and Ambrose, reprinted with permission from the AAPG.<ref name=TA1986 />)]]

[[File:M91FG117.JPG|thumb|300px|{{figure number|6}}Time series of water cut maps from the West Cornelius reservoir, North Markham-North Bay City field, Texas. In this strand-plain reservoir, east-northeastndashwest-southwest-oriented beach ridge macroforms are fairways for water ingress. Tidal mud flat deposits south of the field restrict water influx from this direction (from Tyler and Ambrose.<ref name=TA1986 />)]]

Beach sandstones form as single belts or accrete laterally to form strand plains many kilometers long and several kilometers wide. Modern strand plains such as the Nayarit strand plain of western Mexico show a ridge and swale topography on their surfaces.<ref name=McCubbin /> Mud fills in the interridge swales can act as permeability barriers to lateral flow in the subsurface. One example in the Frio Formation of south Texas is known to have caused the compartmentalization of a beach ridge interval containing several million barrels of recoverable oil.<ref>Reistroffer, J. R., and N. Tyler, 1991, Depositional environments and reservoir compartmentalization within the Frio zone 21-B reservoir, Tijerina-Canales-Blucher field, South Texas (abs.): Transactions of the Gulf Coast Association of Geological Societies, v. 41, p. 559–560.</ref> Water ingress may preferentially occur along the low-lying swales<ref name=TA1986 /> ([[:File:M91FG117.JPG|Figure 6]]).

Beach sandstones form as single belts or accrete laterally to form strand plains many kilometers long and several kilometers wide. Modern strand plains such as the Nayarit strand plain of western Mexico show a ridge and swale topography on their surfaces.<ref name=McCubbin /> Mud fills in the interridge swales can act as permeability barriers to lateral flow in the subsurface. One example in the Frio Formation of south Texas is known to have caused the compartmentalization of a beach ridge interval containing several million barrels of recoverable oil.<ref>Reistroffer, J. R., and N. Tyler, 1991, Depositional environments and reservoir compartmentalization within the Frio zone 21-B reservoir, Tijerina-Canales-Blucher field, South Texas (abs.): Transactions of the Gulf Coast Association of Geological Societies, v. 41, p. 559–560.</ref> Water ingress may preferentially occur along the low-lying swales<ref name=TA1986 /> ([[:File:M91FG117.JPG|Figure 6]]).

Background deposition within the lagoon behind the barrier island is generally mud, but with some sand bodies present. These include washover fans and flood-tidal deltas ([[:File:M91FG192.JPG|Figure 7]]). Washover fans form when storms pitch sand over the barrier bar into the lagoonal area. Flood-tidal deltas develop as a result of the tidal movement of sand through an inlet into the lagoon. These lagoonal sand bodies are characterized by a pinch-out geometry into the lagoonal shales. The shales interfinger with the sandstones, commonly enveloping the sandstones and sometimes isolating them as discrete hydraulic units.

Background deposition within the lagoon behind the barrier island is generally mud, but with some sand bodies present. These include washover fans and flood-tidal deltas ([[:File:M91FG192.JPG|Figure 7]]). Washover fans form when storms pitch sand over the barrier bar into the lagoonal area. Flood-tidal deltas develop as a result of the tidal movement of sand through an inlet into the lagoon. These lagoonal sand bodies are characterized by a pinch-out geometry into the lagoonal shales. The shales interfinger with the sandstones, commonly enveloping the sandstones and sometimes isolating them as discrete hydraulic units.

Washover sandstone complexes may be rather patchy and laterally heterogeneous. Production from washover sandstones in the Glasscock reservoir of the West Ranch field in Texas is described by Galloway.<ref name=Galloway1986 /> Waterflooding has proceeded irregularly with injected water preferentially flowing along the washover channels. As a result, the Glasscock reservoir has the lowest projected recovery factor (38%) of all the major intervals in the West Ranch field.

Washover sandstone complexes may be rather patchy and laterally heterogeneous. Production from washover sandstones in the Glasscock reservoir of the West Ranch field in Texas is described by Galloway.<ref name=Galloway1986 /> Waterflooding has proceeded irregularly with injected water preferentially flowing along the washover channels. As a result, the Glasscock reservoir has the lowest projected recovery factor (38%) of all the major intervals in the West Ranch field.

==References==

==References==

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