Permanent Mooring System for Large Construction and Support Vessels in the Piper Field
- E.A. Lowe (Occidental Petroleum Co.) | V.C. Yin (Occidental Petroleum Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 1980
- Document Type
- Journal Paper
- 547 - 554
- 1980. Society of Petroleum Engineers
- 1.10 Drilling Equipment, 4.2.5 Offshore Pipelines, 4.2 Pipelines, Flowlines and Risers, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.5 Offshore Facilities and Subsea Systems, 1.6.1 Drilling Operation Management, 1.7 Pressure Management, 2.4.3 Sand/Solids Control, 4.5.4 Mooring Systems, 1.6 Drilling Operations
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This paper illustrates the requirement, design, development, and installation of a permanent mooring system for construction support vessels in the Piper field in the North Sea. Key features of the mooring system and its installation procedures are detailed.
The need for support vessels alongside the platform during construction programs offshore has focused attention on the problems of mooring and maintaining station in this service. In the past, mooring systems under storm situations have been designed primarily for open-ocean applications and have not primarily for open-ocean applications and have not catered to the requirements of operating and surviving alongside a fixed platform. In addition, anchor handling and dragging have been primary causes of damage to submarine pipelines. This problem becomes more acute as the number of problem becomes more acute as the number of vessels around the platform increases and the number of moorings over time becomes significant enough to constitute a hazardous situation. The Piper field operators - Occidental of Britain Inc. on behalf of partners Getty Oil Co., Allied Chemical (Great Britain) Ltd., and Thompson North Sea - experienced these mooring difficulties, compounded by poor topsoil conditions, which led to the design and installation of a fixed, permanent anchor-pile mooring system around the Piper A platform. platform. System Description
Eight anchor piles are positioned symmetrically around the Piper A platform to provide a suitable anchor pattern for a multiservice construction vessel to moor alongside the platform in periods of good weather and away from the platform in periods of bad weather. Each anchor pile is approximately 4,000 ft (1219 m) from the center of the platform, and the 1,010-ft (309-m) connecting chain lies on the seabed in a straight line between the anchor pile and the platform. The free end of each chain is connected to a pendant line and marker buoy, which is used to raise the free end of the chain to the surface during connecting or disconnecting operations (Fig. 1).
The anchor-pile system is designed to accommodate construction and tender vessels ranging from medium-sized to third-generation semisubmersibles with operating draft displacements in excess of 40,000 Mg. This system allows for vessels to moor on any of the four sides of the platform and maintain adequate clearance of the mooring catenary from the legs of the platform jacket. The vessel anchor line is "shackled up" to the anchor pile, making it a semipermanent connection. These piles are able to withstand vertical and horizontal forces, thus allowing for adequate "spring constants" throughout the vessel excursion distance even after introducing uplift forces at the anchoring point.
System Design Mooring System
The mooring system consists of eight anchor piles encircling the platform.
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