RIASSUNTO
Abstract
One of the environmental constraints on oil and gas development on the North Slope of Alaska has to do with the need for causeways. Causeways have been used to support docking facilities, drilling and production facilities, and waterflood seawater treatment plants. The design preferred by industry is a solid-fill, gravel causeway. Many governmental permitting and resource agencies feel that the environmental effects of this design are unacceptable. Two solid-fill gravel causeways have been built in the vicinity of Prudhoe Bay. It has been found that some alteration to circulation patterns and localized, temporary changes in nearshore patterns and localized, temporary changes in nearshore fish habitat results from the presence of these structures. While some fear that this puts the fish populations at serious risk, no effects on the local populations at serious risk, no effects on the local fish population have been found. Nevertheless, other, more expensive and technically unproven (in Arctic) options, such as subsea pipelines and bridge type structures, have been proposed, as environmentally preferred alternatives. These should be site specific preferred alternatives. These should be site specific decisions. The increased difficulty in obtaining permits for gravel causeways may result in not permits for gravel causeways may result in not being able to develop some nearshore reservoirs.
Introduction
Climate on the North Slope of Alaska can be quite extreme. For this reason most of the facilities in the oilfield are built in modular fashion
at construction sites in Oregon and Washington. The modules are barged to the North Slope during a summer ""Sea-Lift,"" unloaded at a dock, and then transported by crawlers to their destination where final assembly is completed. Because the nearshore central Beaufort Sea is quite shallow and deep-water ports are not available, dock facilities have been placed on solid fill gravel causeways. The marine transportation needs of the oilfields at Prudhoe Bay are served by on West Dock (Figure Prudhoe Bay are served by on West Dock (Figure 1). The dockhead is approximately 1.75 miles (2.8 km) from shore at the 6-ft (2-m) depth contour. Barge access is maintained by dredging to a depth of 9 ft (3 m). The causeway out to the dockhead was completed in 1976.
To obtain an additional 1 billion barrels of oil from the Prudhoe Bay reservoir, a waterflood project was initiated. A Seawater Treatment Plant project was initiated. A Seawater Treatment Plant (STP) was located offshore with its intake at approximately 12 ft (3.7 m) to provide a year-round source of ice-free water. The West Dock causeway was extended to a total length of 2.7 miles (4.3 km) to provide access to the STP. The pipelines carrying seawater to shore were buried in pipelines carrying seawater to shore were buried in the causeway. A 52-ft (16-m) breach was installed at the base of the extension to facilitate fish passage. passage. The first offshore oilfield to be developed in Arctic Alaska is the Endicott reservoir. There are two man-made, gravel islands to support drilling and production.
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