Prudhoe Bay field
Horizontal Wells: Focus on the Reservoir | |
Series | Methods in Exploration No. 14 |
---|---|
Chapter | Results and conclusions of a horizontal-drilling program at South Pass 62 salt-dome field |
Author | E. P. Mason, M. J. Bastian, R. Detomo, M. N. Hashem, A. J. Hildebrandt |
Link | Web page |
Store | AAPG Store |
Prudhoe Bay field lies on the Alaska coastal plain between Naval Petroleum Reserve No. 4 (NPRA) and the Arctic National Wildlife Refuge (ANWR; Figure 1). Present-day production from Permian-Triassic sandstones and conglomerates of the Ivishak Formation (Figure 2) is approximately 550 MSTBD.
Geologic overview
Several publications relate the exploration process leading to the discovery of Prudhoe Bay field and its geologic characteristics (Morgridge and Smith,[1] Jones and Speers,[2] Jamison et al.[3]). 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 (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.
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 (Figure 4).
Geologic investigations undertaken since field discovery are almost universal in their acceptance of a fluviodeltaic origin for the Ivishak Formation (Detterman,[4] Morgridge and Smith,[1] Eckelmann et al.,[5] Jones and Speers,[2] Wadman et al.,[6] Jamison et al.,[3] Melvin and Knight,[7] Lawton et al.,[8] McMillen and Colvin,[9] Atkinson et al.,[10] Atkinson et al.,[11] Crowder,[12] Begg et al.,[13] Tye et al.[14]). Fluvial strata have been described as braided-river deposits on a coastal plain (Eckelmann et al.,[5] Jones and Speers,[2] Wadman et al.,[6] Melvin and Knight,[7] Lawton et al.,[8] Atkinson et al.[11]) or on a large alluvial fan (McGowen and Bloch,[15] McGowen et al.[16]). Petrophysically defined layers (SMUT Units; Figure 2) constitute a gross reservoir-layering scheme for this interval, which is approximately 180 m (600 ft) thick (Wadman et al.,[6] Melvin and Knight[7]).
Four reservoir-depletion mechanisms (gravity drainage/gas-cap expansion, waterflooding, miscible-gas flooding, and gas cycling) operate simultaneously at Prudhoe Bay (Figure 5; Szabo and Meyers[17]). 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
- ↑ 1.0 1.1 Morgridge, D. L., and W. B. Smith Jr., 1972, 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.
- ↑ 2.0 2.1 2.2 Jones,
- ↑ 3.0 3.1 Jamison,
- ↑ Detterman,
- ↑ 5.0 5.1 Eckelmann,
- ↑ 6.0 6.1 6.2 Wadman,
- ↑ 7.0 7.1 7.2 Melvin,
- ↑ 8.0 8.1 Lawton,
- ↑ McMillen,
- ↑ Atkinson,
- ↑ 11.0 11.1 Atkinson,
- ↑ Crowder,
- ↑ Begg,
- ↑ Tye,
- ↑ McGowan,
- ↑ McGowan,
- ↑ Szabo,