Line Type Optimization of the Flexible Jumper for New Generation Subsea Suspended Manifold Production System

A new generation of subsea production system with the suspended manifold as the major characteristic was proposed to solve the disadvantages for hard to be discarded and recovered for the traditional subsea manifold fixed in seabed. Here, the flexible jumpers connecting the dry trees in the subsea functional chamber to the suspended manifold, can not only provide enough mooring forces as the mooring system, but also transport oil and gas from dry trees, which is an indispensable part of a complete new generation of subsea production system. So how to optimize the flexible jumpers to guarantee a good hydrodynamic performance is quite essential. In this paper, a steep wave type of flexible jumper is optimized by changing the suspended height, connection width, and position and diameter of the buoyancy block. The result shows that the location and the size of the buoyancy block both have a great influence on the distribution of the mechanical property and the line type of the flexible jumper while the influence of suspended height and connection width is very small. Calculations and analysis demonstrated that changing the position of the buoyancy block has no effect on the maximum tensile force of the flexible jumper, but the farther the buoyancy block is from the seabed, the larger the minimum bending radius of the flexible jumper is. Meanwhile, the larger the diameters of buoyancy block becomes, the larger the maximum tensile force is, and the smaller the minimum bending radius will be.

Three-Dimensional Mechanical Analysis of Flexible Jumper Installation

This paper presents a simple method to study the installation process of a flexible jumper lowered into deep water by use of cables in a 3D space. Based on the catenary theory, the initial configuration of the installation system can be obtained easily. Then an iterative procedure, which uses force equilibrium and compatibility requirements as convergence criteria, is adopted to establish the final configuration considering the environmental loads. The internal force, bend radius and displacement of the flexible jumper are also obtained by finite-element discretization. The acquired results are compared with those derived from OrcaFlex finite-element model, in order to verify the accuracy and reliability of the proposed method. The influence on the minimum bend radius and maximum axial tension of the flexible jumper due to the difference between the lowering cable lengths, is also studied. The approach presented throughout this paper can offer some suggestions in regards to the installation of a flexible jumper in practical engineering.

Offshore Monitoring of Snorre A TLP TTR Jumpers

Four sensors were installed on the Snorre A TLP (Tension Leg Platform) on 16th April 2014 and retrieved on 10th May 2014, to document motions of the vessel, top tensioned riser (TTR) and flexible jumper connecting the TTR (Top Tensioned Riser) with the topside piping. The data recorded represents 3828 data sets. Associated significant wave height and peak period is synchronous data extracted from the Miros wave measurement radar and stored in the environmental data base. The SmartMotion riser sensors are certified for service in the Wellbay. The sensors are modelled into the OrcaFlex (1) “calibration” analysis model in order to simulate the motion responses in the same format as recorded offshore (accelerations and rates of rotation), and to carry out verification of the OrcaFlex model by comparing both raw data and filtered/integrated derivatives. This work provides a basis for life extension of the Jumpers and provides valuable feedback to design and analysis of TLP and Spar Jumpers between TTRs and topside Headers.

Singing Mitigation in an Export Riser via Liquid Injection: A Field Case Study

Flexible Risers are prone to the generation of high amplitude tonal noise, i.e. a so-called singing riser. Recently, severe vibrations and high noise levels were encountered on the turret of an FPSO in the Norwegian Sea, resulting in significantly reduced production. The vibrations could be attributed to pulsations generated either by a flexible jumper (connecting topside to turret), the gas lift riser or the gas export riser. Field measurements showed that the most likely source was the 10 inch gas export riser. Due to the vibrations, a reduced production limit was set. A field measurement campaign was started to inject liquid into the export risers to provisionally increase production, while in the meantime permanent solutions were evaluated and installed. Liquid was injected batch wise and continuously. The main field trial was initiated by a batch of MEG (mono ethylene glycol) (2 times 500 liters) followed by continuous injection of small amounts of MEG. Between settling periods, the gas export rate was increased in steps until vibrations were detected. At detection, the MEG injection rate was increased until vibrations/pulsations disappeared, after which gas export was increased again. This process was repeated to maximum gas flow rate, after which the liquid injection and gas export were similarly stepwise decreased. During this test, the gas export could be increased tenfold with moderate liquid injection rates (up to a maximum of 25 l/hr). Similar tests were done with TEG as injected fluid. However, TEG was far less efficient in suppressing the singing. This is attributed to the higher viscosity of the TEG at the injection temperatures and the method of injection.

COBRA Riser Concept for Ultra Deepwater Condition

Offshore ultra deepwater field is being promising as the future of oil and gas reserves. However, the development of ultra deepwater field posed many challenges, in particular, on the selection of the riser concept. Long suspended length of riser will significantly increase the vessel payload. High external hydrostatic pressure on the riser will increase the probability of collapse failure. Large dynamic motions of the vessel and large vessel offset yields potential buckling issues at the touch-down-point (TDP). In addition, potential fatigue problems due to vessel motions and soil-riser interactions also present at TDP area. Large current speed in deepwater field might also lead to vortex induced vibration (VIV) which eventually will contribute to significant fatigue damage for particular riser sections. By looking into these challenges, it is very important to select the most appropriate riser concept for the ultra deepwater field. Catenary Offset Buoyant Riser Assembly (COBRA) as newly developed hybrid riser concept offers a solution to overcome the challenges in ultra deepwater field. In general, COBRA consists of a catenary riser section with a long-slender sub-surface buoyancy module on top which is tethered down to sea bed via two mooring lines. The catenary section from top of the sub-surface buoy is connected to the floater by a flexible jumper. This flexible jumper can effectively absorb the floater motions, which give significant improvements for both strength and fatigue performance on the overall system. As a hybrid riser concept, this concept offers cost effective solution by avoiding all the expensive bottom assemblies that normally needed for a hybrid riser concept. This paper focuses on COBRA riser concept specifically for Santos Basin Central Cluster region at 2200 m water depth. It is observed that there is common sudden change phenomenon on the current direction in Santos Basin area. The effect of bidirectional current is analyzed, and the comparison with unidirectional current is discussed thoroughly. The analyses are focused on the global strength design performance under extreme environmental load and global fatigue design performance of the riser due to wave induced and VIV induced. The results clearly indicate that COBRA riser concept has a robust design and it is feasible for 2200 m water depth, in particular for Santos Basin Cluster Region area. It is also shows that COBRA riser has sufficient strength performance even for extreme bidirectional current.