3D computational modelling of subsea pipeline-soil interaction - for application in the design of controlled lateral buckling
Lead Research Organisation:
University of Oxford
Department Name: Engineering Science
Abstract
Background
In the offshore oil and gas industry, subsea pipelines are vital components of the infrastructure for extracting, processing and transporting hydrocarbon products. These pipelines are frequently required to operate at high pressure and high temperature (HPHT) relative to the ambient subsea environment. The resulting tendency for axial expansion, combined with frictional restraint from the seabed soil, causes large compressive forces to build up. Since pipelines are relatively slender structural elements, they are susceptible to bar buckling: either upheaval buckling in the case of a buried pipe, or lateral buckling in the case of an on-bottom pipe (laid directly on the seabed). At present, only the latter approach is economically and technically feasible in deep water. Indeed controlled lateral buckling is the only practical solution for pipelines operating at HPHT temperatures, above 120 Celsius.
For on-bottom pipelines, lateral buckling is virtually inevitable, and the design objective is to control the buckling process. This is done by initiating buckles in pre-determined locations using triggers (e.g. snake-lay, sleepers, buoyancy modules) to ensure that the predicted lateral displacements, bending stresses and (usually) plastic strains, are not excessive. Operation of a subsea pipeline involves numerous shutdowns and restarts, so lateral buckling is a cyclic process in which the pipe moves back and forth across the seabed. This motion is predominantly normal to the pipeline axis, and because the amplitudes involved are large - typically at least 10 or 20 pipe diameters - there is severe plastic distortion and remoulding of the near-surface seabed material, with soil being ploughed into mounds or 'berms' in front of the pipe (Fig. 1). Direct numerical simulation of this behaviour (e.g. using finite element analysis) remains extremely challenging, and in practice greatly simplified pipe-soil interaction models are used. The pipe also tends to move vertically while it moves laterally, and there is a particularly complex coupling between these two degrees of freedom. Finally, there is a significant component of cyclic axial movement as adjacent lengths of pipe feed into a buckle during restarts, and feed out during shutdowns.
Industrial partner
Crondall Energy - background
Crondall Energy is an expert consultancy, providing independent technical services in floating production, subsea technology, flow assurance, pipeline engineering and subsea system design. Crondall Energy employ about fifty engineers worldwide, including twelve Subsea and Pipeline Engineers based in Aberdeen and Newcastle. Our clients are predominantly the major oil and gas operating companies such as BP, Chevron, Shell, Total, and Woodside.
In the offshore oil and gas industry, subsea pipelines are vital components of the infrastructure for extracting, processing and transporting hydrocarbon products. These pipelines are frequently required to operate at high pressure and high temperature (HPHT) relative to the ambient subsea environment. The resulting tendency for axial expansion, combined with frictional restraint from the seabed soil, causes large compressive forces to build up. Since pipelines are relatively slender structural elements, they are susceptible to bar buckling: either upheaval buckling in the case of a buried pipe, or lateral buckling in the case of an on-bottom pipe (laid directly on the seabed). At present, only the latter approach is economically and technically feasible in deep water. Indeed controlled lateral buckling is the only practical solution for pipelines operating at HPHT temperatures, above 120 Celsius.
For on-bottom pipelines, lateral buckling is virtually inevitable, and the design objective is to control the buckling process. This is done by initiating buckles in pre-determined locations using triggers (e.g. snake-lay, sleepers, buoyancy modules) to ensure that the predicted lateral displacements, bending stresses and (usually) plastic strains, are not excessive. Operation of a subsea pipeline involves numerous shutdowns and restarts, so lateral buckling is a cyclic process in which the pipe moves back and forth across the seabed. This motion is predominantly normal to the pipeline axis, and because the amplitudes involved are large - typically at least 10 or 20 pipe diameters - there is severe plastic distortion and remoulding of the near-surface seabed material, with soil being ploughed into mounds or 'berms' in front of the pipe (Fig. 1). Direct numerical simulation of this behaviour (e.g. using finite element analysis) remains extremely challenging, and in practice greatly simplified pipe-soil interaction models are used. The pipe also tends to move vertically while it moves laterally, and there is a particularly complex coupling between these two degrees of freedom. Finally, there is a significant component of cyclic axial movement as adjacent lengths of pipe feed into a buckle during restarts, and feed out during shutdowns.
Industrial partner
Crondall Energy - background
Crondall Energy is an expert consultancy, providing independent technical services in floating production, subsea technology, flow assurance, pipeline engineering and subsea system design. Crondall Energy employ about fifty engineers worldwide, including twelve Subsea and Pipeline Engineers based in Aberdeen and Newcastle. Our clients are predominantly the major oil and gas operating companies such as BP, Chevron, Shell, Total, and Woodside.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/R513295/1 | 01/10/2018 | 30/09/2023 | |||
| 2123112 | Studentship | EP/R513295/1 | 01/10/2018 | 31/03/2022 | Tianyu Li |