Maintaining subsea equipment can be a complex and expensive endeavor, particularly in deepwater operations. Riser-based well interventions and workovers are necessary operations that while significantly improving production, can also induce considerable fatigue on the wellhead. There is a continuous drive to provide innovative solutions that reduce the cost and time involved in high-pressure interventions, while simultaneously increasing the lifespan of the equipment and field. To meet this need, we developed a high-pressure flexible joint which was recently recognized at the Offshore Technology Conference for the “Spotlight Award on New Technology
The Dual-Barrier 10K Flexible Joint
can be used in place of a traditional tapered stress joint to contain fluids and react the tension within the riser, as well as to accommodate the motion of the vessel up to a 10-degree angle of rotation. When used to replace a bottom stress joint, the significantly lower moment imparted to the wellhead allows an operator to perform more workovers over the life of the well. The 7.22" internal bore diameter enables passage of the most common completion, workover and intervention tools needed to extend the life of the wells and the field.
The smaller envelope of the flexible joint, which itself is just over five feet in height, allows a smaller intervention vessel to conduct high-pressure interventions using a top-tensioned riser without a stress joint or telescopic joint. Thus, the operator can select from a variety of sizes of workover vessels, and is no longer restricted to large, costly and slow-to-mobilize multi-purpose rigs. The benefit of this rigless intervention is that the well comes online sooner and at a lower cost.
When performing subsea interventions in shallow water using tapered stress joints, the entire riser system is very stiff, resulting in a narrow weather window for operations. By replacing the stress joints with flexible joints, the riser system becomes substantially less rigid. This flexibility can open the vessel’s watch circle allowing operations to proceed under much rougher sea states than with stress joints. This can also reduce the likelihood of having to perform an emergency disconnect.
The most unique feature of this flexible joint
is its innovative dual-barrier design. The seal bearing provides the first barrier and is optimized for high-pressure containment and fluid resistance. The second barrier is provided by the load bearing which is designed for low rotational stiffness and fatigue strength. Because each bearing is optimized for its intended function, this avoids the compromises inherent in a single-bearing flexible joint design. Furthermore, the load bearing functions as a redundant seal to improve reliability and capability over a single-bearing design, providing a second barrier unavailable with a stress joint, conventional flexible joint or other components of the riser system.
The flexible joint is rated to 10,000psi and hydro-tested to 15,000psi, with additional safety factors verified with an ultimate burst pressure of 32,000psi. This pressure capability is well beyond what has been fielded in different flexible joint applications to date and demonstrates a significant leap forward towards flexible joints rated for up to 20,000psi working pressure.
Proposal to delivery of the first two flexible joints took only 23 weeks. They were manufactured and DNV certified prior to delivery in August and September of 2017 and have been in service since installation on the intervention vessels in late 2017.