Subsea rigid jumpers are designed to meet numerous criteria including thermal and pressure effects, environmental and riser / pipeline interaction loads, slugging, and other field specific requirements. Jumper VIV can be a concern in fields with strong bottom currents. Without the benefit of detailed VIV fatigue analysis, designers must rely on experience and engineering judgement on placement of strakes if VIV is identified as a concern. VIV mitigation is even more challenging because the jumpers can contain numerous long and short design options to accommodate tolerances for subsea well locations and installation tolerances of subsea PLETS and manifolds. This paper will discuss a case study on optimization of 12 M-shaped jumpers designed for a sour service application in Gulf of Mexico. VIV fatigue assessment of the preliminary jumper design and the methodology adopted to optimize the jumper design and placement of VIV suppression will be discussed. Challenges in meeting high target fatigue life due to sour service application will be discussed. The key challenges whilst optimizing an acceptable VIV suppression solution are the assumed effectiveness of strakes, cost / available inventory of strakes, and physical limitations for placement of strakes. This paper will highlight the trade-offs that are required to strike a balance between strength and fatigue design requirements when using straked buoyancy modules vs. regular strakes. The paper will also highlight the current limitations in design code that relies on standards developed for pipeline application. An alternative method / modification to the DNV F105 approach used to calculate the cross-flow induced in-line VIV fatigue damage is also discussed.

Traditionally, shallow water wells have been drilled from fixed platforms, jack-ups or moored drilling rigs. Recently there has been increased interest in performing operations on these wells using new generation of Dynamically Positioned (DP) rigs, driven by available capacity of these rigs and environmental regulations that restrict laying anchors on the seabed. Shallow water offshore drilling operations present a set of unique challenges and these challenges are further amplified when operations are performed on older wells with legacy conductor hardware with newer DP vessels and larger BOPs. The objective of the paper is to present challenges that occur during drilling in shallow water and discuss mitigation options to make these operations feasible through a series of case studies. Key challenges to optimizing riser operability and rig uptime are discussed. Potential modifications to the upper riser stack-up and rig deck structure for maximizing operational uptime are discussed. Riser system weak point assessment is presented along with solutions for mitigating risks in case the wellhead or conductor structural pipe is identified as the weak link. Selection of the drilling rig can have significant impact on wellhead fatigue response. Some criteria for rig selection based on drilling riser and wellhead system performance is presented with the objective of optimizing the fatigue performance of the wellhead and conductor system. Wellhead fatigue monitoring solutions in combination with physical fatigue mitigation options are presented to enable operations for fatigue critical wells.

For ultra-deepwater subsea wells, a riser system is required to conduct completion, intervention/workover and end of life activities. For ultra-deepwater riser systems with high temperature and pressure requirements, the intervention riser system often requires vessel interface optimization to achieve acceptable design response. The upper riser can be configured in several different ways, each with its own benefit from a safety, risk and performance perspective. This paper compares the riser response for various vessel interfaces for ultra-deepwater applications. As discussed above, intervention riser structural response is sensitive to the riser configuration at the vessel interface. For a typical intervention riser, due to ultra-deepwater and high tension requirements, the functional tension load may utilize up to 40% of yield strength thus decreasing the capacity available to accommodate bending and pressure loads. Vessel operators have options to modify the system configuration to improve the strength and fatigue response of the riser. The different vessel interface options include the tension lift frame (TLF) to vessel interface, the top tension application method and the use or otherwise of a surface tree dolly. Upper riser assembly (URA) loads may be optimized by use of rotary wear bushings, a cased wear joint assembly or flexjoints as a part of the stack-up. The various riser-vessel interface options are evaluated and compared in this paper. This paper highlights the riser design challenges for ultra-deepwater applications.

This paper presents two case studies of the seismic analysis of high pressure riser and conductor systems used on shallow water fixed platforms (approximately 120m water depth) offshore Newfoundland and Labrador, Canada. The case studies presented consider the Hebron and White Rose extension Husky gravity-based concrete platforms. A methodology is presented to assess the dynamic and resonant response of each conductor and riser system to seismic loading using a fully integrated conductor and platform interaction model. Seismic loading is an application of an earthquake-generated agitation to a structure. This occurs at contact surfaces either with the ground, or with adjacent structures, or with gravity waves. Nonlinear time history analyses of the riser system subjected to various ground motion records are performed to simulate the seismic load. Design considerations that drive the HP riser design are discussed. The paper addresses the intricacies of the gravity base concrete platform-riser system interaction, initial configuration and dynamic seismic response. The riser and conductor system response is used to determine HP riser connector and centralization requirements. The learnings taken from the detailed modeling method are presented along with the advantages of this methodology.

The offshore drilling industry is advancing technologies to extend deep water drilling technologies and attain feasibility of operations at deeper depths and higher pressures. However, shallow water operations themselves pose a certain unique set of challenges that need to be addressed with customized and innovative solutions. While shallow water poses certain benefits and conveniences to the operations, like ease of retrieval and better access to wells, there are significant challenges in terms of operational down time caused by limited operability and poor drilling riser and subsea hardware fatigue performance. Shallow water operations do not have the advantage of deep water drilling where the motions and loads imparted to the subsea blowout preventer (BOP) are relatively decoupled and damped out by hydrodynamic damping from the significant length of the water column. Thus, the vessel motions and wave hydrodynamic loads imparted on the riser are transferred to the wellhead and subsea hardware. In this paper the fatigue challenges encountered for drilling wells in 530 ft water depth from a sixth generation moored semi-submersible rig are explored. The fatigue loading is critical for the subsea tree connector which is characterized by a high stress amplification factor (SAF). Multiple riser space-out solutions were evaluated including fairings, helically-grooved buoyancy, joints with rope, and modifications to the telescopic joint each of which will be presented in the paper along with combination of different damping parameters to optimize the fatigue performance. The paper will present the subsea tree connector fatigue performance for different riser space-out options and make recommendations for future operations with similar conditions. Other challenges encountered in fatigue evaluation will be discussed. This will highlight the current assumptions and unknowns in data that can form the subject of evaluation for a future joint industry study.