Flowline Bundles: The "End" Solution
Authors: Willis D.A. , Sewell W.R. 
Published: October 2008

This paper describes from a Contractor k viewpoint the methods and techniques associated with the design, fabrication and construction of â??long' bundles with particular emphasis on the integration of subsea equipment into the towhead structures. The advantages of deploying â??long' bundIes with integrated towheads are illustrated with cost comparisons where subsea structures are installed separately. The paper describes how bundles can be installed within congested developments with little disruption to existing facilities that can continue to produce oil and gas throughout the installation sequence.

INTRODUCTION

Flowline bundles installed by the controlled depth tow technique have become an established way of laying infield pipelines to connect subsea developments with export facilities. The idea was developed over fifteen years ago, and the technique of towing bundles into position has now been refined to the extent that up to twenty pipes can be installed, with associated chemical injection lines and umbilicals, in a single carrier pipe up to 6 km in length.

Like all successful and innovative ideas, the â??state of the art' for bundle technology has continued to be extended. Using proven theories and methods, and with adequate research and development, it is conceivable that a bundle up to 10 km in length could be installed with process, control or well head equipment integrated into the towhead.

The viability of small oil and gas developments, in the North Sea, Gulf of Mexico, Brazil and other areas of the world, depends to a large extent on the economics of connecting them to existing host facilities and floating production systems. Field evaluations should also consider the possibility of staged developments where remote reservoirs can be brought on stream at different times to spread the capital investment. This flexibility can be achieved by designing flowlines and subsea systems so that they can be installed in stages as pipeline bundles with integrated towhead structures.

THE BUNDLE CONCEPT

The technique of installing pipelines in bundles has been used for many years for applications on land. The main advantages are that space can be saved and the ease of installation that results when more than one pipeline is installed simultaneously. This is shown to great effect where pipeline bundles have been installed within directionally drilled sleeves under rivers or other obstacles, and where wayleaves are at a premium. The economic and environmental benefits of bundles are also significant for land-based applications.

The need to develop small offshore reservoirs in the UK North Sea during the late 70's, generated the need to lay relatively short lengths of pipelines and umbilical cables between subsea production facilities and host platforms. A natural progression following experience gained on land, was to construct these pipelines as bundles and to protect them by encasing them within a carrier pipe. The advantages became obvious and although other methods of construction still have their place, by the early 80's bundles had become established.