Abstract

In August, 1985, GIDS completed a full year operating cycle in the Alaskan Beaufort Sea. Drilling operations were routine and the structure sustained no detectable damage from ice or other environmental factors. This paper reviews the logistical and ice monitoring programs employed during this period. The successful rig move to a second drill site is also described.

Introduction

Exxon Company, U.S.A. acquired leases in the Cape Halkett area in the Alaskan Beaufort Sea in OCS Sales 71 and 87 in 1982 and 1984 (Figure 1). Construction of a conventional granular fill island was initially considered as the means for drilling an exploratory well on the "Antares" prospect. However, conventional island construction would have been very costly due to the distance from sources of good quality fill material, the 49 ft. water depth, and the instability of the land-fast ice sheet. In August, 1983, Exxon contracted with Global Marine to furnish an alternative reusable structure, the Concrete Island Drilling System (CIDS), to provide a means of drilling in this area (Figure 2).

The purpose of this paper is to review the performance of the rig, the ice monitoring program and the logistical support scheme through the first annual operating cycle. Other papers by Wetmore1, Phillips and Chen2, and Jahns, Petrie and Lockett3 cover design, construction and initial mobilization of GIDS, and performance of the spray ice barrier built around the structure at Antares.

Annual Operating Scenario

Environmental conditions and regulatory Bowhead whale stipulations in the Alaskan Beaufort generally constrain operations from a mobile structure to a single drill site each year. The major phases during the initial 1984-1985 operating season were:

  1. August - Tow into the Beaufort to the Antares drill site and load equipment and supplies.

  2. September-October - Standby due to regulatory restrictions during the Bowhead whale migration.

  3. November-April - Drill and production test one vertical and one directional well.

  4. May-July - Standby to await open water

  5. August - Tow to the "Orion" drillsite and resupply.

Logistics

The massive size of the CIDS structure allows sufficient consumables storage to drill two to three moderate depth wells without resupply. The basic support plan during the first season was to barge major supply items during the summer, and to fly personnel and 1ight freight from Dead horse by helicopter. A modest amount of material was hauled by rolligons once the ice stabilized in the 1ate winter, when this was more cost-effective than flying.

The initial supply offloading to CIOS on August 14 to 18, 1984 required two barges from Seattle and one from Prudhoe Bay and commenced shortly after CIDS was set on bottom at the Antares site. These supplies were sufficient to drill two wells and keep cms running for a year. A total of 1.8 million gallons of diesel fuel, 1500 tons of bulk mud and cement, 1200 tons of tubulars and 1000 tons of other supplies and equipment were loaded.

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