RIASSUNTO
Abstract
Belmont Island was a man-made oil drilling and production island located approximately 8,100 feet offshore of the City of Seal Beach, California in about 42 feet of water. The island was located on State Oil and Gas Lease PRC 186, which contained approximately 1,225 acres of tide and submerged lands located within the Belmont Offshore Field in Orange County, California. During the 40-year active life of the Island, the wells produced approximately 28 million barrels of oil and 24 million cubic feet of natural gas. The State received over $40 million revenue and the operations grossed over $240 million. ExxonMobil terminated oil and gas production in 1994 due to declining production rates.
This fixture in the waters off Seal Beach, survived nearly fifty years as the State's first offshore oil production facility, Belmont Island became the first man-made oil production island removed from the ocean waters off the California shoreline. After a nearly five year permitting process, the physical removal required 21 months, and was completed in January 2002 with no reportable accidents and no environmental incidents. All of the Island's components were completely removed except for components buried below the natural seafloor.
The Belmont Island project provides a snapshot of the key issues and technical challenges facing decommissioning projects in today's regulatory climate. Such challenges included the handling of hydrocarbon contaminated materials in the caisson core, cutting and removal of lead painted concrete and steel surfaces, and the logistical challenges of handling island materials on a gradually smaller work surface. This paper will provide an overview of these challenges and the approaches developed by the project team to address these challenges.
Facility Location
Belmont Island was an oil exploration and production facility found approximately 8,100 feet offshore from the City of Seal Beach, California (Figure 1, Project Site Location Map). Belmont Island was located at latitude 33° 43' 18.19""N and longitude 118° 07' 28.77""W. The island facility was positioned 3,500 feet southeast of the southeastern tip of the Long Beach, California breakwater; and directly offshore of the Alamitos Bay Marina entrance and the mouth of the San Gabriel River. The island facilities were located on State PRC 186 in approximately 42 feet of water.
Facility History
The Belmont Island installation project began in 1947 with the production of conceptual drawings by the Marine Exploration Company. Monterey Oil Company began construction of the caisson core and North Wharf in 1953. The general construction history of the offshore facility is as follows:
1953-1954: The island's caisson core was constructed by placing a mound of sand approximately 15-feet deep on the seafloor, driving sheet piles into the sand mound to form a 75-foot diameter circular cofferdam, and filling the cofferdam with small rock and sand. Wooden piling driven into the center of the caisson core was used to support a concrete deck that capped the top of the caisson. The island's North Wharf was constructed and submerged pipelines were installed connecting the island to an onshore production terminal.
1957: A steel tower was installed at the south side of the island. The steel tower was constructed of four steel H-beam columns and was anchored to the seafloor with four 12-inch wide flange piles. The South Span was added to bridge the south tower to the island's caisson core. Connecting stairways were also added.
1958: The East Wharf, shop, mud tank, crane pedestal and mezzanine deck were constructed in 1958. The East Wharf was constructed of pre-cast concrete piles and steel H-beam piles supporting a concrete structure. Concrete columns supported the mezzanine deck.
1960: A subsea electrical cable was installed and the island was converted to the shore power.
1962: A system of interconnected tubular steel bracing was installed on the North Wharf bearing piles.