Abstract

As offshore drilling and production continue to move into ever deeper water, supporting the weight of a steel riser becomes a major design issue. For dry tree systems, the problem is further exacerbated when high pressure reservoirs are encountered and heavier thick-wall risers are needed. One solution with significant potential is steel pipe over-wrapped with composite material, combining a durable and fluid tight bore with the exceptional strength and reduced weight of carbon fiber reinforced epoxy. This paper summarizes work performed under RPSEA project 07121–1401 to design a lightweight riser joint as part of a surface BOP drilling system, for a water depth of 3 048 m (10,000 ft) and having a 103,4 MPa (15 kpsi) pressure rating.

Introduction

Surface BOP (SBOP) systems in deepwater have been a novel way to significantly reduce the amount of time and CAPEX associated with drilling a well. Many operators believe this technology is the model for cost-effective field development in ultra-deepwater. However, at increased depths, supporting the additional weight of the riser and its associated equipment becomes a driving factor, and its impact on the floating platform can be limiting, if not prohibitive. This is particularly true when high pressure thick-wall risers are needed. Design of the riser also has its constraints; increasing material strength increases the risk for metallurgical failure as high-strength steels are more susceptible to embrittlement and stress cracking, and increasing wall thickness increases weight and fabrication may not be feasible.

This paper summarizes work performed under RPSEA project 07121–1401 to design a lightweight composite-reinforced steel riser joint as part of a surface BOP drilling system for ultra-deepwater high pressure wells. The design basis is a single barrier riser for a tension-leg platform (TLP) or spar in 3 048 m (10,000 ft) of water and having a 103,4 MPa (15 kpsi) pressure rating. Project funding was provided through the NETL/RPSEA ultra-deepwater program. The project started in January 2009 and was completed in September 2011.

The RPSEA design is in essence a conventional full-bore steel drilling riser joint with the tube body section over-wrapped with composite material. Like a conventional riser joint, the steel member is an assembly of two end couplers welded to each end of straight pipe. End couplers, in addition to the flange, include a thick-wall section for handling the joint and engaging with the spider, followed by a series of tapered grooves related to the traplock metal-to-composite interface (MCI), a feature at both ends of the joint to incorporate the composite and steel members. The steel assembly is over-wrapped by filament winding. Successive layers of continuous carbon fiber roving wetted with epoxy are wound, creating a multi-layered angle-plied laminate. Composite thickness and laminate architecture are determined based on required hoop and axial strengths. An illustration of the RPSEA design is presented in Figure 1.

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