Development of a New Heavy Duty Post Lay Burial System for Oil Field Cables
Authors: Machin J.B. , Spencer A.G. , Fisher R. 
Published: October 2008

A new heavy-duty post lay burial system has been developed. The system consists of a towed plow capable of burying oil field umbilicals and other heavy undersea flexible products to a depth of 2.0 m in water depths ranging to 1500 m. This heavy-duty plow has been designed to operate continuously at tow forces of up to 150 Te in order to provide deep burial in some of the strongest seabed soils found in the world. The plow structure has been fabricated with a 3.0 m radius throughout the product path in order to allow satisfactory handling of the newer generation of oilfield flexible cabling and flowline products.

Specifically designed for carefully controlled diverless operation, the burial system is outfitted with a heavyduty product loading manipulator in order to allow loading of the product into the plow after deployment and without diver intervention. Surveillance and control equipment allows the plow to track and bury cables laid onto the seabed. The new system has completed sea trials and a number of offshore projects in the North Sea. This paper describes in some detail the design and operation of this new plow, including the first results from these recent exercises and burial operations.

Background

The manufacturer of the plow, Perry Slingsby Systems (PSS) has previous experience in the design, development, manufacture and supply of plowing systems predominantly to the telecommunications and military markets. These systems have been tailored to handle relatively light duty and reasonably flexible products.

As the decline in the telecommunications market has continued worldwide, associated sub-sea cable burial projects are diminishing or being deferred. However, there has been a growth in the oil extraction activities in the North Sea, particularly an increase in the development of satellite wells from existing platforms.

The resulting requirement for the connection of services between these step-out wells and the host platforms, in the form of sub-sea power and multi-service controlumbilicals, has led to the need for a burial system which iscapable of handling and burying these larger diameter and stiffer products, reliably and economically to potential burial depths of 2.0 m and in arguably the most challenging seabed conditions in the world.

A number of contracts engaging in these burial activities were scheduled during 2001 and PSS were commissioned to provide a suitable burial equipment solution. Following a review of the capabilities of the existing family of PSS cable plows it soon became apparent that the common core design concept of these successful machines could be built upon to develop a new generation of compact, but heavier duty systems. The plow configuration as eventually conceived is illustrated in figure 1.

Figure 1. The Heavy Duty Plow concept.(Available in full paper)

Plow System Specification

The plow, named HDCP1500 (Heavy Duty Cable Plow 1500), was designed and constructed to provide a range of trenching at up to 2.0 m depth, depending on the product mechanical properties and the characteristics of local soil conditions.