Cement-Bentonite Cut Off Walls: A Comparison of the Hebron and Hibernia Bund Wall

Abstract

The Hebron Project is currently underway in Newfoundland and is expected to provide significant benefits to the province. The Hebron oil field is located in the Grand Banks offshore the island of Newfoundland. The field will be developed by a Gravity Based Structure (GBS) designed to hold 1.2 million barrels of crude oil and a Topsides deck that will contain living amenities and drilling and production capabilities. Similar to the Hibernia platform constructed in the 1990s, construction of the Hebron GBS will begin in a dry dock in Great Mosquito Cove then will be towed to a Deep Water Site (DWS) nearby for completion. The platform will be completed by mating the GBS and the Topsides module and then towed to the field for installation. In the past, Hibernia had a Bund Wall across Great Mosquito Cove constructed of an inner and outer rock berm with impervious till in between to create the dry dock. Initially, Hebron considered using rows of sheet piles or a type of rock berm across Great Mosquito Cove to restrict water from flooding the dry dock. However, the dry dock is currently fabricated by a large embankment dam (the Bund Wall) consisting of several sizes of crushed stone and a cement-bentonite cut off wall in the center. The cement-bentonite cut off wall is made of a slurry that hardens to form a low permeability wall in the center of the Bund Wall. The implementation of this cut off wall provided savings in material volumes and decreased the water seepage flow rate into the dry dock. The amount of material required for the Hebron Bund Wall was approximately a third of the volume used for Hibernia and the water seepage into the drydock was decreased by a minimum of 50% compared to Hibernia. This paper investigates the benefits of a cement-bentonite cut off wall through a comparison of the Hibernia and Hebron Bund Wall.