J-Lay and Steep S-Lay: Complementary Tools for Ultradeep Water

Abstract

Abstract The pipelines are major components of the oil and gas production. With Ultra deep water development, the increasing of assisted recovery and zero-flare policy, pipelines specifications are much more elaborate: fatigue resistance due to cyclical operational loads and frequent shutdowns, thermal insulation for flow assurance purpose. They are often short and associated with many singularities, termination or inline structures. The design of pipelines must take into account walking and buckling, lay out in congested areas, sometimes with geohazards issues. The paper will expose the design of the different pipelines and associated components and describe how the contractors have met these challenges, improved the laying efficiency with using the J- lay method or the steep Slay, which is adapted from conventional laying method continuously improved since the seventies with a deep water application resulting from the revisited strain criteria on the laying ramp. The S-lay methods are much more appropriate from the pipeline fabrication point of view, and appear as a better option for the laying of relative long lines such as gas trunk line or long tie back. The J lay method appears as a natural configuration from the catenary point of view and is much more appropriate to the installation of in line structures. The paper will illustrate with practical applications that these two methods are not opposed but are complementary tools and have each their own domain of excellence in the production and recovery of the hydrocarbon resources. Introduction The driving phenomena for deep water pipelines have drastically evolved over the last ten years with the development of deep water fields. The key driver for the design of the field layout and the flowlines is undoubtedly the flow assurance of multiphase fluids. This has led to a significant increase of insulated flowlines, which has had a great impact on the overall behavior of pipelines on the sea bed. The use of wet insulation materials such as polypropylene and polyurethane has resulted in a general reduction in the submerged weight of production flowlines, this in combination with the very soft soil conditions found in deep water locations has led to the significant increase in pipeline movements induced by pressure and temperature of the internal fluids. These movements known as pipe walking and lateral buckling have been the subject of much discussion within the offshore pipeline industry in recent years /1/, /2/, /3/, /4/. The details of these phenomena are not discussed in this paper, however the influence they have on the installation methods used for deep water pipelines will be addressed. The field layout selected for a particular offshore development has a significant influence on the pipelines and in particularly the installation techniques. In deep water fields, which are dominated by subsea wells, the field layout tends to be very different from those selected for more conventional water depths.