Modelling of ice rubble accumulations in the North Caspian Sea

In the shallow waters of the North Caspian Sea, ice rubble can accumulate around island structures, impairing the function of escape, evacuation and rescue (EER) systems and impeding access to quay areas. In this paper, a method is outlined for characterizing ice movement events, defining the geometry of the main structure and protection structures, and characterizing the rubble that can accumulate adjacent to them. The approach is fully probabilistic, relying on the statistical characterization of ice drift, ice thickness, rubble height and rubble extent based on locally acquired data. The plan geometry of the structures and the rubble accumulations are defined on a regular grid. When protection structures or gravel berms are present, the rubble can bridge the gaps, thereby protecting the installation from further rubble accumulations. This effect has also been modelled probabilistically based on local observations. An important objective of the work is the assessment of downtime for drilling operations. Ice incursions and rubble build-up can prevent the launch and transit of evacuation craft, and also prevent quay access for barges. Explicit consideration is made for EER launch areas, barge footprints, evacuation routes through ice and quay areas that need to be kept free of ice rubble. Based on the probabilistic representation for the ice rubble accumulations, downtime estimates are made for EER and quay access for which examples are shown in the paper. The present approach is used for assessing the effect of different structure geometries and berm layouts.