An analytical parametric study of pipeline embedment into the seabed

Quinn Snook, Ryan Gregory, Hodjat Shiri

In the proceedings of: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Posters

ABSTRACT: Subsea pipelines are a very important part of extracting hydrocarbons from offshore developments. They are an effective way to transport extracted hydrocarbons from offshore platforms back to shore where they can be processed and distributed. When a pipeline is laid across the seabed, it can sink into the seabed by displacing or compacting the solid below it under the heavy weight of the steel pipe, concrete coating, and the pipe contents. Pipeline embedment is affected by the installation method, the weight of the pipeline, the movement of the sea around the pipe and pipe laying vessel, and the rate at which the pipe is laid. It is also important to consider that pipe can be embedded by both vertical and horizontal movement. Different combinations of horizontal and vertical movement can cause deeper embedment and more complex conditions. The addition of content inside of the pipe during a hydrotest or normal operation may also affect pipe embedment since the additional weight may cause the pipeline to sink more. This paper presents an analytical parametric study that examined the effect of some of the key factors affecting pipe embedment. Variables were changed one at a time while the other variables are kept at default values, and the effects on pipe embedment were monitored and analyzed. The study revealed several important trends. It was observed that several soil and pipe parameters affect the vertical force required for embedment in mostly linear patterns.

RÉSUMÉ: Les pipelines sous-marins jouent un rôle très important dans l'extraction d'hydrocarbures des aménagements offshore. Ils constituent un moyen efficace de transporter les hydrocarbures extraits de plates-formes offshore vers le continent, où ils peuvent être traités et distribués. Lorsqu'un pipeline est posé sur le fond marin, il peut s'enfoncer dans le fond marin en déplaçant ou en compactant le solide en dessous sous le poids lourd du tuyau en acier, du revêtement de béton et du contenu du tuyau. L'installation du pipeline dépend de la méthode d'installation, du poids du pipeline, du mouvement de la mer autour du tube et du navire poseur et de la vitesse à laquelle le tube est posé. Il est également important de considérer que le tuyau peut être encastré à la fois par des mouvements verticaux et horizontaux. Différentes combinaisons de mouvements horizontaux et verticaux peuvent provoquer une incrustation plus profonde et des conditions plus complexes. L'ajout de contenu à l'intérieur du tuyau pendant un test hydrostatique ou normal peut également affecter l'emboîtement du tuyau, car le poids supplémentaire peut faire en sorte que le pipeline s'enfonce davantage. s que les autres variables sont conservées à leurs valeurs par défaut. Les effets sur l'intégration du tuyau ont été surveillés et analysés. L'étude a révélé plusieurs tendances importantes. Il a été observé que plusieurs paramètres de sol et de conduite influent sur la force vert 1. INTRODUCTION Subsea pipeline embedment is an important aspect of pipe-soil interaction. Embedment depth is affected by different stages of the pipeline life cycle. During installation, the embedment depth is affected by the installation method, the weight and stiffness properties of the pipe, the sea state and vessel motion at the time of laying, and the lay rate. Embedment is affected by the orientation of forces acting on the pipe, such as vertical and horizontal forces. When the pipeline undergoes hydrotesting, the increased weight of the pipeline will cause further embedment. During operation, the embedment may be affected additionally. Many uncertainties exist in modeling embedment and simplifications are necessary. Models exist for approximating pure vertical resistance for undrained and drained soil conditions. In this study, an analytic parametric study was performed to examine the effect of various pipe and soil parameters has on the vertical force required to embed a subsea pipeline at a given depth. This paper presents an analysis of how the force required to achieve a specified level of pipeline embedment changes as a function of multiple soil properties and pipeline properties. The properties were changed within ranges that were determined based on a review of previous studies related to subsea pipeline embedment and other studies of subsea soil properties. Values of these parameters used by previous studies, or based on field

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