Osprey Pipelines - Cook Inlet, Alaska

Abstract

Abstract Three pipelines were installed by the pull method to the Forest Oil, Redoubt Shoal Field, Osprey Platform in Cook Inlet, Alaska. This project took place in the summer of 2002 and utilized new technology in a number of areas. The pipes were all heavy wall seamless tubulars designed to remain stable in tidal currents up to 13-ft/sec. The pipes were coated with three layer polypropylene for abrasion resistance and reduction of friction factor. The pipeline shore approaches were 3 each 12.75-in diameter × 1800-ft long drilled approaches that were initiated from a bluff location 200-ft above Cook Inlet. Two different drilling and casing techniques were used and each is discussed. The pipelines, up to 8.625-in in diameter, were pulled into the platform through 234.5-in radius pull tubes completely contained within the 14-ft diameter platform legs. The pull loads were highest on pipeline entry into the pull-tubes. A simple chain jack designed and fabricated for the project was used to exert pull loads in excess of 270,000-lbs to successfully pull in the risers. Risers and pipelines were installed using simultaneous application of tension from the platform based chain jack on the pipe end and a barge deployed pull wire engaged 500-ft down line. Pipeline System The offshore reaches of the Osprey pipelines are shown in Fig 1. Osprey pipelines general arrangement. Fig 2. Osprey platform & bluff crossed by pipelines is a photo of the project that shows the Osprey platform and about 2 miles distant the 200-ft high bluff that was crossed by directional drilling. The pipelines were designed to meet the requirements of 49CFR192 Transportation of Natural and other Gas by Pipeline: Minimum Federal Safety Standards and 49CFR195 Transportation of Hazardous Liquids by Pipeline. All offshore pipe was seamless quenched and tempered material. Pressure design. The offshore portion of the pipeline system consists of three parallel pipes. These are:8.625-in × 0.750-in wall thickness X-52 to convey produced fluid (a mixture of oil, water & dissolved gas) from the Osprey Platform to the Kustatan onshore processing facility. Maximum allowable operating pressure (MAOP) is 3705-psig. Considering pressure only, there is a corrosion allowance of 0.323-in for the pipeline and 0.238-in for the riser.8.625-in × 0.875-in wt X-60 for return of injection water from the Kustatan processing facility to the platform under high pressure. MAOP is 5000-psig. Considering pressure only there is a corrosion allowance of 0.376-in for the pipeline and 0.276-in for the riser.6.625-in × 0.750-in wt X-52 spare line suitable for gas, hydrocarbon liquid, or injection water transportation. The design MAOP is 5000-psig in liquid service, 4177-psig in gas service. Considering pressure only in gas service there is a corrosion allowance of 0.308-in for the pipeline and 0.113-in for the riser. The derated pressure for gas service arose due to the requirement of 49CFR192.619 to hydrotest the riser to 1.5 × MAOP compared to the 1.25 × MAOP test specified by 49CFR195 for liquid service.