Best practice geotechnical characterization and pipe-soil interaction analysis for HPHT pipeline design

This paper summarizes best practice cost-effective geotechnicai design of high pressure high temperature (HPHT) pipelines, with an emphasis on HPHT lines in deep water, that are susceptible to lateral buckling and axial walking. It presents guidance on (i) tools for optimal geotechnicai characterization of shallow seabed conditions along flowline routes and (ii) techniques to assess pipe-soil interaction parameters for input to pipeline structural modeling. Recent research into pipe-soil interaction measurement tools and analysis techniques has resulted in rapid advancements that are being quickly utilized in practice. Advanced pipe-soil interaction techniques, firmly rooted in soil mechanics theory and linked to the operational sequence of the pipeline through cycles of start-up and shut-down, are presented. They are used to demonstrate benefits that can be realized on typical projects to reduce pipeline walking predictions and the associated mitigation measures such as hold-back anchors. Recommendations cover the appropriate selection of characterization tools and analysis techniques based on project-specific requirements such as seabed geotechnicai complexity, pipeline operating conditions, project timing, mitigation strategies for global stability and the desired approach to risk management and use of the observational method. The results, observations and conclusions presented in this paper represent the culmination of several years of research and development in pipe-soil interaction, as well as our experience on recent projects around the world where these techniques have been employed. The paper offers recommendations to guide both geotechnicai studies and pipeline engineering work, and unlock benefits from maintaining close integration of these two disciplines through the design and operation of a pipeline.