TY - BOOK
T1 - The as-laid embedment of subsea pipelines /by Zachary J. Westgate
AU - Westgate, Zachary
PY - 2013
Y1 - 2013
N2 - The behaviour of a subsea pipeline is strongly influenced by its level of embedment into the seabed. In deep water, the in-service embedment of a pipeline is mainly controlled by the lay process during installation. The as-laid embedment is notoriously difficult to assess, due to uncertainties associated with the near surface soil properties, the dynamic movement of the pipe caused by the sea state and resulting vessel motion, and the largedeformation nature of pipe-soil interaction at the seabed. Prior to this work, the industry approach to assessing as-laid embedment was to first assess the static embedment as if the pipe were lowered statically onto the seabed, allowing for the effect of the pipe catenary on the touchdown load, and then to amplify this embedment by an empirical adjustment factor, not linked directly to the soil conditions, pipe properties or lay process. Data sets obtained from as-laid field surveys of subsea pipelines were combined with numerical simulations of offshore pipe laying and physical model testing of the dynamic pipe embedment process to investigate the mechanisms that govern the as-laid embedment of seabed pipelines. The field surveys comprise embedment data for five different pipelines from three different hydrocarbon-producing regions. The pipeline properties, soil conditions, lay vessel characteristics, and sea states varied widely across the five case studies, which allowed benchmarking of existing and newly proposed calculation methods for assessing as-laid embedment. The numerical simulations were used to assist with interpretation of the field surveys, by simulating the pipe response due to the measured vessel motions and sea states. The physical model testing, performed in a geotechnical centrifuge, involved well-controlled idealisations of different aspects of the lay process.
AB - The behaviour of a subsea pipeline is strongly influenced by its level of embedment into the seabed. In deep water, the in-service embedment of a pipeline is mainly controlled by the lay process during installation. The as-laid embedment is notoriously difficult to assess, due to uncertainties associated with the near surface soil properties, the dynamic movement of the pipe caused by the sea state and resulting vessel motion, and the largedeformation nature of pipe-soil interaction at the seabed. Prior to this work, the industry approach to assessing as-laid embedment was to first assess the static embedment as if the pipe were lowered statically onto the seabed, allowing for the effect of the pipe catenary on the touchdown load, and then to amplify this embedment by an empirical adjustment factor, not linked directly to the soil conditions, pipe properties or lay process. Data sets obtained from as-laid field surveys of subsea pipelines were combined with numerical simulations of offshore pipe laying and physical model testing of the dynamic pipe embedment process to investigate the mechanisms that govern the as-laid embedment of seabed pipelines. The field surveys comprise embedment data for five different pipelines from three different hydrocarbon-producing regions. The pipeline properties, soil conditions, lay vessel characteristics, and sea states varied widely across the five case studies, which allowed benchmarking of existing and newly proposed calculation methods for assessing as-laid embedment. The numerical simulations were used to assist with interpretation of the field surveys, by simulating the pipe response due to the measured vessel motions and sea states. The physical model testing, performed in a geotechnical centrifuge, involved well-controlled idealisations of different aspects of the lay process.
KW - Pipelines
KW - Geotechnical
KW - Subsea
KW - Offshore
KW - Pipe laying
KW - Soil mechanics
KW - Lay effects
KW - Shear strength
M3 - Doctoral Thesis
ER -