This paper reviews the design and construction methods, and construction rates for Exxon Company, U.S.A.'s winter 1980-81 construction projects on the North Slope of Alaska. The projects include construction of 1) 90 miles of ice roads (ten-miles on floating ice), 2) two artificial (manmade) gravel islands off the Sagavanirktok River delta in ten-feet and 18 feet water depths, 3) two sheet pile enclosed drill sites on natural barrier islands approximately 60 miles east of Prudhoe Bay, and 4) the development of two upland gravel sources, one near Prudhoe Bay and one near Pt. Thomson.
For exploration drilling offshore in the Alaskan Beaufort Sea, it is important to be able to accurately evaluate alternative drill sites and plan for construction due to the present seasonal restrictions on drilling. The technology and experience gained during the exploration drill site design and construction may be used during planning for future field development facilities and structures.
Emphasis is given to the unique design criteria and actual construction procedures and production rates for winter constructed manmade gravel islands and the sheet pile enclosed drill sites. These are the two principle alternatives being considered for exploration and development structures in shallow water.
Exxon Company, U.S.A. has actively been involved in exploration drilling on Alaska's North Slope for the past nine years. The majority of drilling operations have been onshore in the Point Thomson area approximately 50 miles east of Prudhoe Bay. Activity over the past few years has included work offshore in the Duck Island area, roughly ten-miles east of Prudhoe Bay.
Past drilling operations in both areas have been classified as exploratory and no permanent gravel roads to the areas could be built. As a result all operations are supported by all-terrain vehicles, ice roads in the winter, and barges in the summer. Figure #1 illustrates the proximity to Prudhoe Bay of Exxon's activities.
Drilling onshore in the Pt. Thomson area has been supported from trucked gravel pads built in the winter. These pads are typically five-feet thick and cover roughly 150,000 square feet of surface area. Drill site gravel pads in this area require two to three weeks to construct. To support construction and drilling in the area each year, Exxon has built a 60 plus mile ice road along the coast from Prudhoe Bay over grounded ice (frozen to bottom).
In 1978 Exxon constructed its first manmade gravel island. Duck Island Pad #1 was constructed in roughly four-feet of water approximately 14 miles northeast of Prudhoe Bay, near the mouth of the Sagavanirktok River. This island had six feet of freeboard and a 400 foot diameter drilling surface. Offshore construction activity was completed in approximately one month. The ice was grounded in the area when construction began. The ice was ripped up with dozers and pushed aside. Gravel was hauled ten-miles over grounded ice roads and dumped in the hole. Drilling from this island was restricted to fall and winter months. Operations were supported from Prudhoe Bay using ice roads. Two wells were drilled from this artificial island over a two-year period.
