ABSTRACT

Ice gouging is a destructive incident to subsea pipelines in Arctic regions. Trenching and backfilling have been selected as the most efficient way to protect the pipeline. Studies indicate that remolded backfill materials with considerably less stiffness than native soil can significantly complicate soil failure mechanisms and pipe trajectories. In this paper, a numerical model was developed using coupled Eulerian-Lagrangian (CEL) method to investigate the influences of a backfilled trench on the seabed soil failure mechanism and the pipeline response with two model configurations. The study showed that the conventional simplification of assuming homogeneous seabed soil on trenched backfilled pipelines might misinterpret pipeline behavior and soil failure mechanisms.

INTRODUCTION

Due to the depletion of older oil fields, the oil and gas industry is now paying more attention to new techniques and resources for oil extraction. The Arctic regions represent one of the unexplored hydrocarbon resources, with a high percentage of pristine resources (Gautier et al., 2009). However, some other obstacles and hazards could arise at various stages of exploitation in an ice environment, such as ice gouging (Abdalla et al., 2008). Water currents and winds in shallow areas cause ice gouging, which states the drifting of ice features like icebergs on the seabed. Pipelines are buried into the seabed as a practical and economical approach to protecting pipelines against ice gouging because ice keel-pipeline contact would be destructive to pipeline safety. Nonetheless, the ice gouge exerts multiple substantial stresses on the seabed, leading to soil failure mechanisms such major subgouge displacements, frontal mounds, and side berms (Fig. 1). As a result, the buried pipe will be impacted by the ice gouge and undergo a complicated path of lateral, vertical, and axial stresses and strains.

The most common source of backfilling is the excavated soil. Because of the drilling machine's contact with the excavated soil and mixing with the seawater, the soil is disturbed and has less shear strength.

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