Underwater wellhead completions with portable atmospheric cellar

摘要

This invention concerns means for protecting a marine wellhead (including the Christmas tree) on an offshore hydrocarbon-producing platform from damage due to fire. Special means are provided to place the wellhead a small depth, e.g., 25 to 50 feet, below the water surface under the deck of the offshore platform. These special means include a horizontal plate supported by the platform and sealed to the upper end of the casing. A cylindrical housing, called a "portable cellar," is lowered from the platform and seals with the horizontal plate. The cellar housing extends above the surface of the water. Water is then pumped out of the sealed cellar so that work on or through the wellhead can be done in a normal open-air environment. After the operation is performed on or through the wellhead, the cellar is removed, the water again surrounds the marine wellhead, so that, in case of fire, it cannot be damaged by heat.