Challenges and Solutions for Deep water Subsea Pipeline Design: A Case Study on Chinese Longest Distance Multiphase Pipeline Tie-Back in LS25-1 Project in South China Sea

The Lingshui25-1 gas field is located in the northern sea area of Qiongdongnan Basin, and the water depth is 850m ~ 1000m. The gas production from the LS25-1 field is facilitated through a 115 km long, 20-inch export pipeline, which ties back to a shallow jacket platform. This paper delineates the design and analytical approaches employed for the 20-inch export multiphase pipeline, addressing significant design and installation challenges. These include pipeline route optimization, pipe-soil interaction analysis, bottom roughness and span fatigue analysis, and a composite fatigue assessment encompassing VIV span fatigue, thermal fatigue, and slugging fatigue at subsea scarp locations. As of October 2023, the pipeline has been successfully laid, accompanied by subsequent post-installation surveys. This paper additionally elucidates the installation processes and post-survey span conditions, contextualized within the realm of subsea engineering.