Case History: Ice Island Drilling Application and Well Considerations in Alaskan Beaufort Sea

Abstract

Summary During Winter 1988–89 Chevron U.S.A. Inc. and Mobil Oil Production Co. constructed an ice island with seawater spray Production Co. constructed an ice island with seawater spray to drill the Karluk prospect. A land-drilling program was modified to drill the exploration well to 11,190 ft total depth (TD). The project was completed in the allotted time and within its budget, despite one of the most volatile winters on record. Introduction The North Slope of Alaska contains not only North America's most prolific oil field, but also its greatest promise for major oil prolific oil field, but also its greatest promise for major oil discoveries. North Slope fields hold one-quarter of U.S. recoverable reserves. The 350-sq-mile Prudhoe Bay field, which produces 1.5 million BOPD, is the most famous oil field, yet 10 other oil and gas fields have been found. Most fields extend offshore to some degree, and two lie entirely offshore. Shallow water depths of less than 25 ft extend from a few to more than 10 miles offshore along the entire 1,000-mile north Alaska coast. Many coastal onshore prospects have been explored, but the shallow offshore areas have been investigated far less. Early offshore exploratory efforts relied on the string of existing barrier islands for drillsites. With sufficient site preparation, these islands were adequate as drilling locations but limited for exploration. Select-site location was achieved, at a far greater cost, with the construction of gravel islands. For example, Tern Island was built in 1982 in 20 ft of water with 313,000 yd3 of gravel for $18 million. Gravel-island construction required large, readily available gravel sources; the mobilization and use of much heavy equipment; and a great deal of time. Often an entire winter drilling season was spent on construction alone. These permanent islands could have been converted into production sites, but for most exploratory ventures, this capability was not needed. The high cost of gravel islands, which grew even higher at deeper water depths, led to the use of bottom-supported drilling vessels in the early 1980's. This special fleet consists of the Canmar SSDC/MAT (with a 25- to 80-ft water-depth rating), the Beaudril Molikpaq (for 45- to 120-ft water depths), and the Glomar Beaufort Sea I C.I.D.S. (for 30- to 55-ft water depths). Unfortunately, these unique vessels are still limited to water depths is greater than 25 ft and require high day rates. The concept of using ice as a drilling platform was field-tested as early as 1974. It was not until 1985, however, that Amoco Production Co. constructed Mars Island and became the first company Production Co. constructed Mars Island and became the first company to drill from an operational-spray ice island. The island was 5 miles offshore and about 100 miles west of Prudhoe Bay in 25 ft of water. It successfully supported the drilling and testing of the 8,000-ft Mars prospect, Well OCS-Y-0302 No. 1. During Winter 1987–88, Esso prospect, Well OCS-Y-0302 No. 1. During Winter 1987–88, Esso Canada experienced similar success with an 8,000-ft well on Angasak Island, built in 21 ft of water in the Canadian Beaufort Sea. During Winter 1988–89 Chevron U.S.A. and Mobil Oil Production Co. constructed Karluk Island in 24 ft of water to evaluate the Production Co. constructed Karluk Island in 24 ft of water to evaluate the 12,000-ft exploration prospect well OCS-Y-0194 No. 1, located 25 miles northeast of Prudhoe Bay (Fig. 1). The partners chose an ice island for this single-season exploratory well because of its location, its compatibility with the environment, and its economy.