Ice-Soil-Pipeline Interactions Using Coupled Eulerian-Lagrangian (CEL) Ice Gouge Simulations - Extracts from Ice Pipe JIP
Authors: Banneyake Ranil , Hossain M. Kabir , Eltaher Ayman , Nguyen Thanh , Jukes Paul 
Published: December 2011

Continuously increasing energy demand combined with depleting traditional fields have pushed the industry to explore oil and gas into frontiers such as arctic regions and ultra deepwater. These areas pose new challenges to the industry in all aspects of exploration and development. In the arctic regions, subsea pipelines must be designed to survive extremely harsh conditions such as low temperatures, thermally induced fatigue, and high stresses from ice gouging. In a study supported by a recent Ice Pipe JIP, ice-soil-pipeline interactions of buried pipelines were investigated by numerical simulations using select modeling techniques. This paper presents results from this study using the Coupled Eulerian-Lagrangian (CEL) technique, and attempts to identify the important interactions between the governing parameters.

Ice gouging is a major subsea pipeline safety concern in the arctic regions, in which iceberg grounding can cause large soil movements around a buried pipeline inducing excessive deformation and high stresses, severely affecting its integrity. Pipeline design in arctic regions, therefore, must account for potentially serious effects of ice gouging. Current industry knowledge of the phenomenon is limited and the subject Ice-Pipe-JIP was an effort to help enhance the understanding.

It is believed that the results presented here will help pipeline engineers understand the effects and interactions of ice gouging depth, angle and width, pipeline's burial depth and soil cover, etc in clayey or sandy seabed. The results will help contribute to increased confidence in the formulation and development of arctic pipeline design best practices for the subsea pipeline engineering community, going forward. Also, the paper demonstrates CEL-based finite element analysis (FEA) as a competent and dependable numerical tool for modeling, analyzing and studying soil-structure problems with characteristic extreme large soil deformations, which are generally unamenable to more traditional Lagrangian numerical techniques.

Introduction

Faced with ever increasing demand for oil and gas and with the traditional fields depleting [Ref. 1], the industry is putting increasing emphasis on exploration and development of frontier areas such as the arctic regions. The Arctic Circle contains 22% of the undiscovered, technically recoverable hydrocarbon reserves in the world, 84% of which is estimated to be in the offshore [Ref. 2]. However, many challenges exist with the exploration in the arctic offshore: harsh climate, remote location, limited daylight, ice cover, sensitive ecosystem, etc [Ref. 3], including ice gouging (or scouring). Ice gouging poses an important design consideration for any on-bottom pipeline or offshore structure in the arctic regions.

In the arctic and sub-Arctic areas it is common to observe ice gouging such as in the shallow Beaufort Sea and offshore Newfoundland. Environmental forces drive ice features (icebergs or ice-ridges) that extend deeper than the water column imprinting scours in the seabed. Ice scouring can result in significant seabed surficial soil movements, and has the potential to cause devastating effects on buried seabed pipelines. The pipelines are thus designed to be buried below the mudline so that contact with the gouging ice is avoided. However, surrounding sub-gouge soil displacements can get transmitted to the pipeline inducing excessive deformation; therefore, accurate determination of sub-gouge soil displacements and the impact on the pipeline is critical for appropriate design of burial depth.