J-Curve Pipeline Installation Practical Issues

Abstract

ABSTRACT Drilling and production in deep water have now reached the 2500 to 3000 ft water depth range. Pipeline installation in these depths benefits considerably from the use of J-curve technology; however, practical issues confront the contractor in terms of vessel requirements, equipment layout and the development of the special procedures needed to meet safety and reliability standards presently achieved by the conventional S-curve method. This paper describes specialized equipment, outlines procedures and provides an overview of the progress made to date by the pipeline industry. Methods of welding, tensioning and monitoring the pipe during installation are described. INTRODUCTION J-curve pipelaying represents a logical extension of the industry capability into deep water. The method is attractive as the bending stresses are low, the horizontal force required for station keeping is within the capability of dynamic positioning systems and the use of modular towers allows derrick barges and moderately sized support vessels to be equipped for pipeline installation. Such versatility also makes this method of interest in areas having few conventional laybarges. Although the concept has been discussed by several authors previously (Ref. 1), the J-curve method has recently received increased attention due to aggressive exploration in deep water prospects. Indeed several pipelines are planned to be installed by this method in the next three years and remaining near term technical issues are being addressed by operators, installation contractors and engineers. The technical challenges being targeted in the near term represent aspects related to vessel productivity and pipe stress control. This paper examines the practical aspects of a modular stalking tower for J-curve laying considering:pipe handling;welding;tensioning; andpipe monitoring. The first two are productivity related, and the second two are part of stress control and pipe safety. To focus the discussion, the profile of representative deep water pipeline project is established. This serves to examine the merits of various options on a systematic basis. Lastly, the viability of converting a laybarge to J-curve laying while retaining conventional horizontal make-up is discussed and a concept presented. FIELD REQUIREMENTS The suitability of the J-curve method depends on oceanographic currents, seafloor conditions, water depths along the route, and pipe characteristics. The parameters vary regionally, but some general requirements can be established. Deep water areas which have been, or are expected to be developed within the next five years include:Gulf of Mexico (1500 to 3000 ft)NW Shetland Is., North Sea (1500 to 2000 ft)Campos Basin, Brazil (to 3000 ft) Oceanographic currents in deep water reflect the steeper slopes and tend to be of an episodic nature and less predictable than in shallow water. High velocity density currents have been measured in several continental slope areas. Cold bottom water spilling over the Wyville Thomson Ridge have produced occasionally bottom currents of 4 ft/sec. (Ref. 2) in the area to the NW of the Shetland Islands. Hurricane induced bottom currents of 8 to 10 ft/sec. have been measured off Hawaii on the continental slope (Ref. 3).