Abstract
Subsea pipelines are commonly employed in the offshore oil and gas industry to transport high-pressure and high-temperature (HPHT) hydrocarbons. The phenomenon of pipeline walking is a topic that has drawn a great deal of attention, and is related to the on-bottom stability of the pipeline, such as directional accumulation with respect to axial movement, which can threaten the security of the entire pipeline system. An accurate assessment of pipeline walking is therefore necessary for offshore pipeline design. This paper reports a comprehensive suite of numerical analyses investigating the performance of pipeline walking, with a focus on the effect of increasing axial soil resistance on walking rates. Three walking-driven modes (steel catenary riser (SCR) tension, downslope, and thermal transient) are considered, covering a wide range of influential parameters. The variation in walking rate with respect to the effect of increased soil friction is well reflected in the development of the effective axial force (EAF) profile. A method based on the previous analytical solution is proposed for predicting the accumulated walking rates throughout the entire service life, where the concept of equivalent soil friction is adopted.
Highlights
Submarine pipelines are important facilities for subsea production systems to transport the products of high-pressure and high-temperature (HPHT) hydrocarbon sources in the offshore oil and gas industry
This paper reports a comprehensive suite of numerical analyses investigating the performance of pipeline walking, with a focus on the effect of increasing axial soil resistance on walking rates
This paper aims to investigate the response of pipeline walking rate with regard to a typical operational stage, where increased axial soil friction in response to the intermittent operational mode of the subsea pipeline is considered
Summary
Submarine pipelines are important facilities for subsea production systems to transport the products of high-pressure and high-temperature (HPHT) hydrocarbon sources in the offshore oil and gas industry. An accumulated axial displacement of over 7 m was unexpectedly observed for a 2000 m long pipeline in the North Sea [2], leading to the collapse of the end connections. The early development of hydrocarbon sources was mainly localized nearshore, with pipelines fully buried in the seabed, and sometimes paved with stones, so that the pipeline could be restricted, resulting in negligible movement. This may not, be the cause of the phenomenon of pipeline walking. There have only been a few investigations related to potential axial movements in pipelines, focusing on aspects such as the relative movement between the pipeline and the concrete coating [3], and the soil friction along the pipeline [4,5]
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