The paper describes the installation analysis for the Matterhorn field pipeline replacement, located in water depths between 800-ft to 1200-ft in the Gulf of Mexico. For this pipeline repair project, the existing 10-in gas pipeline leaving the Matterhorn platform was rerouted outside of the mudslide area and connected to the existing 12-in gas pipeline. The replacement project includes recovering the 10-in pipeline, welding an 8-in pipeline using a reducer and laying down a Pipeline End Termination (PLET). This fast track project faced scheduling, mobilizing and analytical challenges due to its time constraints. The feasibility study of the 10" × 8" reducer was performed and an optimized lay tower angle was proposed considering weather limitation and the ease of equipment handling at different installation phases. An installation fatigue analysis was carried out to assess the fatigue. The pipelines and PLET were installed successfully in July 2009.The maximum allowable sea states were identified for all the pipeline repair and installation phases. The laydown of the 10" × 8" reducer is the most critical installation phase under beam sea and head quarter sea. For the normal pipelay of the 8-in pipelines with the same lay angles, the limiting sea states for the minimum water depth are more critical than that for the maximum water depth. The limiting sea state for the reducer welding to the existing 10-in pipeline was lowered in order to decrease installation fatigue damage in the sagbend. This paper presents an installation analysis for rigid pipeline repair and replacement with different ODs between the existing and new pipelines. The application of the pipeline recovery tool system and the reducer has been confirmed. An optimized lay angle was developed based on the limiting sea states from both dynamic behavior and fatigue assessment.
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