2,803
edits
Changes
Jump to navigation
Jump to search
Created page with "{{publication | image = Methods14Cover.png | width = 120px | series = Methods in Exploration No. 14 | title = Horizontal Wells: Focus on the Reservoir | part =..."
{{publication
| image = Methods14Cover.png
| width = 120px
| series = Methods in Exploration No. 14
| title = Horizontal Wells: Focus on the Reservoir
| part =
| chapter = Results and conclusions of a horizontal-drilling program at South Pass 62 salt-dome field
| frompg = 49
| topg = 65
| author = E. P. Mason, M. J. Bastian, R. Detomo, M. N. Hashem, A. J. Hildebrandt
| link = http://archives.datapages.com/data/specpubs/method14/me14ch04/me14ch04.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=525
| isbn = 0891816658
}}
[[file:mth14ch07f01.jpg|thumb|300px|{{figure number|1}}Location of Prudhoe Bay field, Alaska. Inset maps highlight the ARCO-operated Eastern Operating Area (EOA). ARCO PBU 15-45 is located in the north-central part of the field. Details of Drill Sites 3 and 9 show where lateral MIST projects are under way.]]
[[file:Mth14ch07f02.jpg|thumb|300px|{{figure number|2}}Prudhoe Bay type log depicting formal stratigraphic nomenclature and informal, operationally based reservoir-layering schemes (SMUT Units and Equity Zones). Reservoir properties are generalized, full-field values.]]
Prudhoe Bay field lies on the Alaska coastal plain between Naval Petroleum Reserve No. 4 (NPRA) and the Arctic National Wildlife Refuge (ANWR; [[:file:Mth14ch07f01.jpg|Figure 1]]). Present-day production from Permian-Triassic sandstones and conglomerates of the Ivishak Formation ([[:file:Mth14ch07f02.jpg|Figure 2]]) is approximately 550 MSTBD.
[[file:Mth14ch07f03.jpg|thumb|300px|{{figure number|3}}Regional south-to-north cross section from the Brooks Range to the Beaufort Sea illustrates the stratigraphy and major structural features of the North Slope. Prudhoe Bay field formed where the Ivishak Formation is draped over the Barrow Arch, truncated by the Lower Cretaceous unconformity, and overlain by marine shales. Location is shown in Figure 1.]]
==Geologic overview==
Several publications relate the exploration process leading to the discovery of Prudhoe Bay field and its geologic characteristics (Morgridge and Smith,<ref name=Morgridgeandsmith_1972>Morgridge, D. L., and W. B. Smith Jr., 1972, [http://archives.datapages.com/data/specpubs/fieldst4/data/a010/a010/0001/0450/0489.htm Geology and discovery of Prudhoe Bay Field, eastern Arctic Slope, Alaska], ''in'' R. E. King, ed., Stratigraphic oil and gas field: AAPG Memoir 16, p. 489-501.</ref> Jones and Speers,<ref name=Jonesandspeers_1976>Jones,</ref> Jamison et al.<ref name=Jamisonetal_1980>Jamison,</ref>). Briefly, Prudhoe Bay field lies along the crest of the Barrow Arch, an east-west-trending, Cretaceous anticline formed by the northward thrusting of the Brooks Range ([[:file:Mth14ch07f03.jpg|Figure 3]]). The southern flank of the Barrow Arch dips gently (2°), whereas the northern flank is much steeper. Sandstones and conglomerates of the Ivishak Formation record the north-to-south advancement of shallow-marine and fluvial depositional systems. At Prudhoe Bay, the Ivishak Formation is unconformably overlain by shallow-marine mudstones, limestones, and fine-grained sandstones of the Shublik and Sag River Formations. The Jurassic Kingak Shale forms the seal.
[[file:Mth14ch07f04.jpg|thumb|300px|{{figure number|4}}Generalized structure map on the top of the Sadlerochit Group. Major northwest-southeast- and west-east-trending faults and approximate fieldwide fluid distributions are shown. The white square shows the location of Drill Site 15.]]
Prudhoe Bay field is 52 km long by 19 km wide (32 mi by 12 mi). Structurally, the field occurs between 2500 and 2800 m subsea (8200 and 9200 ft), and original oil- and gas-column thicknesses were 142 m (465 ft) and 122 m (400 ft), respectively. Numerous west-to-east- and northwest-to-southeast-trending faults segregate the reservoir into isolated blocks and, in places, enhance fluid migration ([[:file:Mth14ch07f04.jpg|Figure 4]]).
Geologic investigations undertaken since field discovery are almost universal in their acceptance of a fluviodeltaic origin for the Ivishak Formation (Detterman,<ref name=Detterman_1970>Detterman,</ref> Morgridge and Smith,<ref name=Morgridgeandsmith_1972 /> Eckelmann et al.,<ref name=Eckelmannetal_1975>Eckelmann,</ref> Jones and Speers,<ref name=Jonesandspeers_1976 /> Wadman et al.,<ref name=Wadmanetal_1979>Wadman,</ref> Jamison et al.,<ref name=Jamisonetal_1980 /> Melvin and Knight,<ref name=Melvinandknight_1984>Melvin,</ref> Lawton et al.,<ref name=Lawtonetal_1987>Lawton,</ref> McMillen and Colvin,<ref name=Mcmillenandcolvin_1987>McMillen,</ref> Atkinson et al.,<ref name=Atkinsonetal_1988>Atkinson,</ref> Atkinson et al.,<ref name=Atkinsonetal_1990>Atkinson,</ref> Crowder,<ref name=Crowder_1990>Crowder,</ref> Begg et al.,<ref name=Beggetal_1992>Begg,</ref> Tye et al.<ref name=Tyeetal_1999>Tye,</ref>). Fluvial strata have been described as braided-river deposits on a coastal plain (Eckelmann et al.,<ref name=Eckelmannetal_1975 /> Jones and Speers,<ref name=Jonesandspeers_1976 /> Wadman et al.,<ref name=Wadmanetal_1979 /> Melvin and Knight,<ref name=Melvinandknight_1984 /> Lawton et al.,<ref name=Lawtonetal_1987 /> Atkinson et al.<ref name=Atkinsonetal_1990 />) or on a large alluvial fan (McGowen and Bloch,<ref name=Mcgowenandbloch_1985>McGowan,</ref> McGowen et al.<ref name=Mcgowenetal_1987>McGowan,</ref>). Petrophysically defined layers (SMUT Units; [[:file:Mth14ch07f02.jpg|Figure 2]]) constitute a gross reservoir-layering scheme for this interval, which is approximately 180 m (600 ft) thick (Wadman et al.,<ref name=Wadmanetal_1979 /> Melvin and Knight<ref name=Melvinandknight_1984 />).
[[file:Mth14ch07f05.jpg|thumb|300px|{{figure number|5}}Map of recovery processes active in Prudhoe Bay field. Gravity drainage is the dominant recovery mechanism in the north-central part of Prudhoe, whereas the eastern, southern, and western field margins are under active waterflood and miscible-injectant recovery.]]
Four reservoir-depletion mechanisms (gravity drainage/gas-cap expansion, waterflooding, miscible-gas flooding, and gas cycling) operate simultaneously at Prudhoe Bay ([[:file:Mth14ch07f05.jpg|Figure 5]]; Szabo and Meyers<ref name=Szaboandmeyers_1993>Szabo,</ref>). Each process is managed to work in concert with the existing fluid distribution (expanding gas cap, injected water, and oil), regional geology (2° southward structural dip; intersecting east-west and northwest-southeast fault trends), and field-scale geology. Interbedded conglomerates, sandstones, and mudstones create a spatially variable rock volume containing permeabilities ranging from a few millidarcys to tens of darcys. Tailoring horizontal wells and their completions to suit specific engineering and geologic conditions significantly increases primary and tertiary recovery from fine-grained sandstones and conglomerates in Prudhoe Bay field.
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/method14/me14ch42/me14ch04.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=525 Find the book in the AAPG Store]
| image = Methods14Cover.png
| width = 120px
| series = Methods in Exploration No. 14
| title = Horizontal Wells: Focus on the Reservoir
| part =
| chapter = Results and conclusions of a horizontal-drilling program at South Pass 62 salt-dome field
| frompg = 49
| topg = 65
| author = E. P. Mason, M. J. Bastian, R. Detomo, M. N. Hashem, A. J. Hildebrandt
| link = http://archives.datapages.com/data/specpubs/method14/me14ch04/me14ch04.htm
| pdf =
| store = http://store.aapg.org/detail.aspx?id=525
| isbn = 0891816658
}}
[[file:mth14ch07f01.jpg|thumb|300px|{{figure number|1}}Location of Prudhoe Bay field, Alaska. Inset maps highlight the ARCO-operated Eastern Operating Area (EOA). ARCO PBU 15-45 is located in the north-central part of the field. Details of Drill Sites 3 and 9 show where lateral MIST projects are under way.]]
[[file:Mth14ch07f02.jpg|thumb|300px|{{figure number|2}}Prudhoe Bay type log depicting formal stratigraphic nomenclature and informal, operationally based reservoir-layering schemes (SMUT Units and Equity Zones). Reservoir properties are generalized, full-field values.]]
Prudhoe Bay field lies on the Alaska coastal plain between Naval Petroleum Reserve No. 4 (NPRA) and the Arctic National Wildlife Refuge (ANWR; [[:file:Mth14ch07f01.jpg|Figure 1]]). Present-day production from Permian-Triassic sandstones and conglomerates of the Ivishak Formation ([[:file:Mth14ch07f02.jpg|Figure 2]]) is approximately 550 MSTBD.
[[file:Mth14ch07f03.jpg|thumb|300px|{{figure number|3}}Regional south-to-north cross section from the Brooks Range to the Beaufort Sea illustrates the stratigraphy and major structural features of the North Slope. Prudhoe Bay field formed where the Ivishak Formation is draped over the Barrow Arch, truncated by the Lower Cretaceous unconformity, and overlain by marine shales. Location is shown in Figure 1.]]
==Geologic overview==
Several publications relate the exploration process leading to the discovery of Prudhoe Bay field and its geologic characteristics (Morgridge and Smith,<ref name=Morgridgeandsmith_1972>Morgridge, D. L., and W. B. Smith Jr., 1972, [http://archives.datapages.com/data/specpubs/fieldst4/data/a010/a010/0001/0450/0489.htm Geology and discovery of Prudhoe Bay Field, eastern Arctic Slope, Alaska], ''in'' R. E. King, ed., Stratigraphic oil and gas field: AAPG Memoir 16, p. 489-501.</ref> Jones and Speers,<ref name=Jonesandspeers_1976>Jones,</ref> Jamison et al.<ref name=Jamisonetal_1980>Jamison,</ref>). Briefly, Prudhoe Bay field lies along the crest of the Barrow Arch, an east-west-trending, Cretaceous anticline formed by the northward thrusting of the Brooks Range ([[:file:Mth14ch07f03.jpg|Figure 3]]). The southern flank of the Barrow Arch dips gently (2°), whereas the northern flank is much steeper. Sandstones and conglomerates of the Ivishak Formation record the north-to-south advancement of shallow-marine and fluvial depositional systems. At Prudhoe Bay, the Ivishak Formation is unconformably overlain by shallow-marine mudstones, limestones, and fine-grained sandstones of the Shublik and Sag River Formations. The Jurassic Kingak Shale forms the seal.
[[file:Mth14ch07f04.jpg|thumb|300px|{{figure number|4}}Generalized structure map on the top of the Sadlerochit Group. Major northwest-southeast- and west-east-trending faults and approximate fieldwide fluid distributions are shown. The white square shows the location of Drill Site 15.]]
Prudhoe Bay field is 52 km long by 19 km wide (32 mi by 12 mi). Structurally, the field occurs between 2500 and 2800 m subsea (8200 and 9200 ft), and original oil- and gas-column thicknesses were 142 m (465 ft) and 122 m (400 ft), respectively. Numerous west-to-east- and northwest-to-southeast-trending faults segregate the reservoir into isolated blocks and, in places, enhance fluid migration ([[:file:Mth14ch07f04.jpg|Figure 4]]).
Geologic investigations undertaken since field discovery are almost universal in their acceptance of a fluviodeltaic origin for the Ivishak Formation (Detterman,<ref name=Detterman_1970>Detterman,</ref> Morgridge and Smith,<ref name=Morgridgeandsmith_1972 /> Eckelmann et al.,<ref name=Eckelmannetal_1975>Eckelmann,</ref> Jones and Speers,<ref name=Jonesandspeers_1976 /> Wadman et al.,<ref name=Wadmanetal_1979>Wadman,</ref> Jamison et al.,<ref name=Jamisonetal_1980 /> Melvin and Knight,<ref name=Melvinandknight_1984>Melvin,</ref> Lawton et al.,<ref name=Lawtonetal_1987>Lawton,</ref> McMillen and Colvin,<ref name=Mcmillenandcolvin_1987>McMillen,</ref> Atkinson et al.,<ref name=Atkinsonetal_1988>Atkinson,</ref> Atkinson et al.,<ref name=Atkinsonetal_1990>Atkinson,</ref> Crowder,<ref name=Crowder_1990>Crowder,</ref> Begg et al.,<ref name=Beggetal_1992>Begg,</ref> Tye et al.<ref name=Tyeetal_1999>Tye,</ref>). Fluvial strata have been described as braided-river deposits on a coastal plain (Eckelmann et al.,<ref name=Eckelmannetal_1975 /> Jones and Speers,<ref name=Jonesandspeers_1976 /> Wadman et al.,<ref name=Wadmanetal_1979 /> Melvin and Knight,<ref name=Melvinandknight_1984 /> Lawton et al.,<ref name=Lawtonetal_1987 /> Atkinson et al.<ref name=Atkinsonetal_1990 />) or on a large alluvial fan (McGowen and Bloch,<ref name=Mcgowenandbloch_1985>McGowan,</ref> McGowen et al.<ref name=Mcgowenetal_1987>McGowan,</ref>). Petrophysically defined layers (SMUT Units; [[:file:Mth14ch07f02.jpg|Figure 2]]) constitute a gross reservoir-layering scheme for this interval, which is approximately 180 m (600 ft) thick (Wadman et al.,<ref name=Wadmanetal_1979 /> Melvin and Knight<ref name=Melvinandknight_1984 />).
[[file:Mth14ch07f05.jpg|thumb|300px|{{figure number|5}}Map of recovery processes active in Prudhoe Bay field. Gravity drainage is the dominant recovery mechanism in the north-central part of Prudhoe, whereas the eastern, southern, and western field margins are under active waterflood and miscible-injectant recovery.]]
Four reservoir-depletion mechanisms (gravity drainage/gas-cap expansion, waterflooding, miscible-gas flooding, and gas cycling) operate simultaneously at Prudhoe Bay ([[:file:Mth14ch07f05.jpg|Figure 5]]; Szabo and Meyers<ref name=Szaboandmeyers_1993>Szabo,</ref>). Each process is managed to work in concert with the existing fluid distribution (expanding gas cap, injected water, and oil), regional geology (2° southward structural dip; intersecting east-west and northwest-southeast fault trends), and field-scale geology. Interbedded conglomerates, sandstones, and mudstones create a spatially variable rock volume containing permeabilities ranging from a few millidarcys to tens of darcys. Tailoring horizontal wells and their completions to suit specific engineering and geologic conditions significantly increases primary and tertiary recovery from fine-grained sandstones and conglomerates in Prudhoe Bay field.
==References==
{{reflist}}
==External links==
{{search}}
* [http://archives.datapages.com/data/specpubs/method14/me14ch42/me14ch04.htm Original content in Datapages]
* [http://store.aapg.org/detail.aspx?id=525 Find the book in the AAPG Store]