RIASSUNTO
Abstract
To successfully drill in remote and harsh environment areas, a wide variety of specialized equipment, material and personnel must be mobilized in an orderly manner. Long-range planning consisting of environmental assessment, engineering studies, logistical analysis, equipment selection, and operations scheduling must be accomplished prior to operations. ARCO Alaska, Inc., utilized long-range planning methods in preparation for a three-well Bering planning methods in preparation for a three-well Bering Sea drilling program.
Introduction
In June 1980, ARCO Alaska, Inc., initiated operations to drill three Continental Offshore Stratigraphic Test (C.O.S.T.) wells in the Bering Sea, west of Alaska. The well locations (Figure l), lie in the St. George Basin, the North Aleutian Shelf, and the Navarin Basin in water depths ranging from 270 ft. to 420 ft. The operational environment is characterized by extreme remoteness, lack of established support facilities, hostile meteorologic and marine conditions, and annual incursions of sea ice. The OCS Oil and Gas Leasing Schedule required that the St. George Basin and the North Aleutian Shelf wells be completed by the end of 1982 and the Navarin Basin well in 1983.
Operations and studies were undertaken to: (l) analyse the physical environment of the drilling locations; (2) develop a drilling prognosis and material requirements for each well; (3) define the type of drilling unit required and contract a suitable rig; (4) design, locate and construct support facilities; (5) define the types of air and marine support required and contract the equipment and services; (6) obtain all required permits; and (7) implement several special studies and engineering programs to cope with unique aspects of the programs to cope with unique aspects of the Operation.
ENVIRONMENTAL ANALYSIS OF THE DRILLING LOCATIONS
Onsite Surveys
The onsite investigation of the three locations consisted of biological, shallow geophysical, archeological, and geotechnical investigations carried out in June, July, and August 1980. Biological site surveys were carried out according to U.S.G.S. guidelines by means of otter trawls, underwater television and photography, plankton sieves, benthic grab sampler, and visual observations of birds and marine mammals. Although all three well locations lie in a biologically rich area, it was determined that no significant adverse biological impact would result from the C.O.S.T. well program.
The shallow geophysical investigation consisted of five separate acoustic profiles recorded concurrently. These include a twelve-channel digital water gun recording, analog water gun recording, Mini sparker profile, 40 KHz echo depth sounder, and dual channel side scan sonar. The echo sounder and side scan sonar were also capable of detecting water column anomalies. The survey analysis revealed evidence of possible shallow gas-charged sediments at two of the proposed locations, which resulted in minor repositioning of the wells.
The initial geotechnical analysis was based on dart core samplers and literature search. Operations at the first well site, however, demonstrated that the dart core penetration and recovery was inadequate for proper soils strength analysis. Subsequently, rotory coring was performed at the Navarin Basin location.
NORMAL AND EXTREME METEOROLOGICAL AND OCEANOGRAPHIC CONDITIONS
An abundant supply of data exists concerning the normal oceanographic and meteorological conditions in the Bering Sea. Both public and proprietary sources were used to compile summaries of historically normal conditions.