Salvage and Relocation of Offshore Platform with Minimum Equipment

Abstract

ABSTRACT This paper describes the planning and operations involved in the intact salvage and relocation of a five-well drilling platform in the Gulf of Mexico. The operation employed unique procedures to plug, abandon, and remove existing dry hole wells; to free the below-mudline portions of the platform jacket; and to minimize the size and amount of lifting equipment required. These planning and methods innovations resulted in a significant reduction in heavy lift equipment requirements, with a corresponding reduction in cost of the project. INTRODUCTION Humble Oil &Refining Company's South Pass Block 36 "A" Platform was originally erected in September 1963. This structure was a four-pile, five-well, tender type platform in 165 feet of water. It utilized a special five-well drilling rig sub-structure and derrick which required no rig skidding. The platform foundation jacket weighed 576 tons, and three 250 ton derrick barges were required to originally set it in position (Figure 1). Pertinent features of the jacket (Figure 2) included (1) four 34 inch O.D. main legs, battered 1 in 5, (2) a center 34 inch O.D.; combination non-bearing leg and conductor guide, (3) four 36 inch O.D., skirt pile guides, and (4) a 50 feet × 50 feet square, solid plate "shear box" attached to the bottom of the jacket and extending 28 feet below the mudline. Drilling operations resulted in three unsuccessful wells, and the drilling rig was removed in August 1964. In mid-1966 it was proposed to salvage the foundation jacket for reuse to support a new 62 man self-contained living quarters building in West Delta Block 73, where the water depth was the same 165 feet. The salvage and re-installation of this structure presented four major problem areas which correspond to the four operational phases of the project.Well Abandonment and RemovalThree unperforated wells were left standing. Two required abandonment in conformance with governmental regulations. The required cement plugs had been placed in the third well by the drilling rig. All three had to be cut off below mudline, and if possible, removed prior to moving the jacket.Foundation Jacket RemovalThe dead weight of the jacket plus the frictional resistance of the "shear box" indicated an upward lift in excess of 800 tons would be necessary to remove the structure.Transport of Jacket to New LocationThree methods of transporting the jacket approximately 30 miles in semi-open Gulf waters appeared to be possible.The jacket could be set on a barge, and the barge towed to the new location. This would require over 500 tons of lifting capacity to re-install.The jacket could be made buoyant and towed in a horizontal plane.The jacket could be lifted vertically with the derrick barge crane, held with the crane, and the derrick barge towed to the new location.Installation at New LocationThe "shear box" created a problem at the new location. Although needed at South Pass, it was not needed and assumed to be extremely difficult to install at West Delta.