The ∼18 km long 10" pipeline was installed by MCDERMOTT as part of a gas export modification development in the Gulf of Mexico. The pipeline was initiated with a 97 Te dual-hub PLEM at a water depth of 1535 m. The fast track nature of the project required the PLEM design and fabrication to be carried out in a short time in collaboration with the installation analysts to ensure installability. Initiation of the heavy PLEM at the end of a thin wall pipe in deep water posed considerable challenges in developing an installation methodology. After evaluation of all alternatives, employing an LCV to help with PLEM initiation in a flooded condition was deemed necessary. The LCV crane was deployed after PLEM reached a certain height over the seabed. A sequence of LCV and LV-NO105 movements, pipelay tower angle alteration, and pipe and LCV crane wire payout was followed to transfer the PLEM weight to the LCV crane and rotate it to horizontal. The rigging from a clump weight, which had been installed earlier as merely a contingency hold-back device, was then connected to the PLEM. A sequence of LCV movements, LV-NO105 movements, pipe and crane wire payout was followed to land the PLEM safely on the seabed. The crane wire was disconnected after laying a short length of pipeline on the seabed. The installation procedure was developed such that the sling between the contingency clump weight and PLEM remained slack. The PLEM weight was sufficient to provide the necessary horizontal holdback, after landing in the target box, for normal pipelay. The LCV crane operated in various modes (constant tension and active heave compensation) to ensure a smooth initiation process. Maintaining a smooth synchronization of activities shared between LCV and LV-NO105 was crucial to success of the project.
The simplest and most cost effective foundation to support deepwater subsea structures is a mudmat. As loads and weights increase, the attractiveness of a mudmat foundation disappears and the typical solution has been a costly suction caisson. A hybrid subsea foundation (HSF) was found to be a cost effective and robust alternative. A HSF is a mudmat with four corner piles that provide additional bearing capacity in an effective and cost competitive way. This paper presents the design process, fabrication, and installation of a HSF for two flowline end terminations (FLETs) for a recent deepwater project.
Deepwater development projects require the design, fabrication and installation of a variety of subsea facilities or structures. Shallow foundations (or mudmats) have been used extensively for temporary and permanent subsea structures when the expected loads are relatively moderate.
Oftentimes, subsea structures especially in deepwater projects must be designed to sustain substantial lateral loads and overturning moments coming from product line expansion thrust, jumper loads or other external sources. In recent subsea applications, external loads imposed on a subsea foundation far exceed the bearing capacity and sliding resistance of a typical size shallow (mudmat) foundation.
Owing to the very soft clay conditions that typically exist in deep waters worldwide, the sizes of mudmats have increased, while foldable side-wings and skirts along the outside perimeter have been added to increase the vertical, horizontal and rocking resistance of the mudmat. However, the need to increase the mudmat size to meet the magnitude and complexity of the imposed loads has been challenged by the dimensions and geometry constraints from pipelay installation vessels. Typically, a deep foundation, such as suction pile or a driven pile (within the depth limits of operability of hydraulic hammers) has been the next solution to meet the need for high bearing and overturning moment capacities. However, the deep foundation option is quite costly compared to a typical mudmat foundation. When the loads are exceeding the bearing capacity of a typical mudmat but are not high enough to justify a costly deep foundation, a hybrid subsea foundation (HSF) has become an attractive solution.
Seabed mining in deep oceans has taken on new interests around the world after a hiatus since the initial efforts in the 1970’s. Exploration campaigns using the latest underwater survey and mapping technologies have shown certain ocean floors rich in polymetallic mineral deposits in the forms of SMnN (Seabed Manganese Nodules). The few mining systems developed thus far typically involve a VTS (Vertical Transport System) which has a free-hanging rigid riser with pump(s), and sometimes a buffer, located along it. The free-hanging riser presents a special design challenge because of its long unsupported span, heavy weight, and the lack of tension to control its curvature/bending stress. This paper investigates the dynamic response of such a mining riser during operation and installation in 5000m water depth. The analyses conducted include wave induced riser motions and current induced VIVs (Vortex Induced Vibrations) in an exercise to identify design issues and determine operational limitations. Particular attention is given to the scenario when the riser is deployed with the seabed mining crawler hanging in tandem. It is found that an additional clump weight may have to be added to the riser bottom to improve its lateral stability, VIVs dominates the riser fatigue behavior, and the riser axial response dictates the installation weather windows.
With the increasing global demand for strategic metals, deepsea mining has taken on new interests around the world after a hiatus since the initial efforts in the 1970’s. Polymetallic mineral deposits in the forms of SMnN (Seabed Manganese Nodules) have been found in certain ocean floors in water depth of 4000m to 6000m by using the latest underwater survey and mapping technologies. The few mining systems developed thus far typically consists of a mining supporting vessel, VTS (Vertical Transport System) which has a free-hanging rigid riser with pump(s) and sometimes a buffer located along it, flexible jumper and seafloor mining machine.
In a recent Gulf of Mexico deepwater development project, two hybrid subsea foundations (HSF) were designed, fabricated and successfully installed for two flowline end terminations (FLETs) in approximately 2,170 meter water depth. The HSF is an attractive option when a subsea structure is subjected to substantial lateral loads, vertical loads and overturning moments that cannot be effectively resisted by a typical shallow (mudmat) foundation. A new HSF design methodology was established and a pile head locking system was developed by the project team. This is the first offshore application of the HSF concept utilizing the vertical resistance from the corner piles in addition to their lateral resistance via a custom designed pile head locking system. In configuring the pile head locking system to provide pile head fixity, the gap between the sleeve and the pile became one of the governing factors for design, fabrication and installation of the HSF. This paper presents the case history of the successful project execution covering the detailed design, fabrication and staged installation. Foundation selection during the detailed design stage, description of the pile locking system, preventive measures taken during the fabrication stage, back analysis results from the installation stages and pictures taken by remotely operated vehicles (ROVs) during the FLET HSF installation are presented.
This paper describes the methodology and the required finite element models for highly detailed 3D finite element simulations of trawl gear impact on pipeline. The multi-physics simulation software LS-DYNA was used as solver. The simulation methodology has the following characteristics: (a) high resolution 3D models are used to represent the pipeline including an elasto-plastic material model; (b) a 3D soil model is used that deforms and interacts with the pipeline; (c) simple von-Mises type soil material model; (d) the trawl gear is modeled as rigid 3D bodies with correct geometry and inertia.
The simulations are transient dynamic analyses and include contacts, buoyancy, and gravitational forces. The influence from the water fluid dynamics is modeled using the hydrodynamic added mass approach following DNV-RP-F111. The inertial effects from the pipeline content and coating is modeled in a simplified manner as added masses.
Developed simulation models and the method described are then used to evaluate the influence of several variables on the dent depth due to trawl gear impact on an uncoated field joint. The influence from the following factors were studied: pipeline dimensions, soil support (embedment), internal pressure (no pressure and operating pressure), soil shear strength, and trawl gear impact velocity. The trawl gear, a trawl board and a clump weight, was represented using geometrically accurate 3D models.
It is demonstrated that the developed methodology for simulation of trawl gear impact on pipelines is numerically robust.
When designing a pipeline, it is necessary to do a careful assessment of the loads a pipeline is expected to be subjected to during its design life. All the load cases in the pipeline lifetime are considered: starting from pipe laying, water filling, and pressure testing, to the operational loads caused by pressure, temperature and flow rate of the transported fluid as well as environmental loads and loads imposed by third parties, like dropped objects, fishing gear, dragging anchors, et c.
The effect of the pig gravity on its frictional force was experimentally investigated. The stress distribution of the sealing disc in circumferential and radial direction with the variation of different pig gravities were revealed according to the finite element simulation. Research results indicated that the pig gravity almost has no effect on the frictional force of a pig, since the increased contact force in the lower part of the disc can offset the decreased force in the upper part. The stress distribution of the sealing disc in radial direction indicated that the maximum stress existed at the clamping edge.
Fossil fuels have been serving as the source of energy for almost all practical purpose of human existence, and they are of great importance to the development of the human beings. Fossil energy industry has used pipelines as the most economic, efficient and safe way to deliver oil and gas to terminals (Lesani, Rafeeyan and Sohankar, 2012). In order to maintain a good condition of these pipelines, pipeline inspection gauges (pigs) are periodical used to perform functions such as dewatering, cleaning, inspecting and et.al., and it has become a standard industry procedure now (Botros and Golshan, 2009). Pigs can achieve most efficiency when they run at a near constant speed but will not be effective in case that they run at very high speed. Moreover, excessive and uncontrolled pigging speed can be very dangerous, and often involves various risks such as get stuck in the pipeline or crash with pipeline accessories, especially in gas pipeline (Esmaeilzadeh, Mowla and Asemani, 2009). As a result, prediction on the pig motion to estimate its velocity, position and required driving pressure is particularly important before pigging. Accurate pigging prediction can even help to identify the potential risks and establish risk mitigation strategies (Zhu, Zhang, Li, Wang and Yu, 2015).
The frictional resistance between the pig and the pipeline plays an important role on determining the motion of a pig, and can greatly affect the accuracy of predicted results. Knowledge on the frictional resistance resulted from the soft contact between rubber (sealing disc or cup) and rigid pipe wall is of great importance for the understanding of pigging motion (Tan, Wang, Liu and Zhang, 2014).
AbstractThe Stones project is located in the Walker Ridge (WR) area approximately 200 miles due South of New Orleans in ~9500 feet of water. The host facility is a Floating Production Storage and Offloading (FPSO) vessel with a disconnectable moored turret buoy (BTM) that allows the FPSO to move off site in a hurricane event. Each of the nine moorings are made up of a suction pile – chain – polyester – chain – spring buoy – top chain assembly. These connect to the circumference of the BTM at the keel. The subsea infrastructure, including 2 flow-lines, one gas export pipeline, and two umbilicals, are supported by the BTM. The pipelines and all umbilical fluids, electrics, and fiber are connected or disconnected from the FPSO via dry internal turret connection systems.This paper provides an overview of the transportation and installation of the moorings, turret buoy.Key challenges include water depth world record for FPSO moorings, transportation and handling of the world's largest disconnectable buoy, and project execution during an extreme eddy current event.
Demel, Jasmina (Subsea 7) | Wallerand, Regis (Subsea 7) | Rebours, Nicolas (Subsea 7) | Cafi, Mersina (Subsea 7) | Grelon, Florent (Subsea 7) | Mencarelli, Guy (Subsea 7) | Gioielli, Paulo (ExxonMobil) | Olayera, Olanrewaju (ExxonMobil)
This paper presents a novel, flexible, and economic solution used to mitigate anticipated pipeline walking of a flowline on a deepwater development, offshore West Africa, in about 1000 m of water depth. Aspects from conceptual, design, fabrication and installation are presented for this recently used anchoring solution.
The most common way to mitigate pipeline walking in the Deepwater offshore industry has been holding the flowline from the end opposite to the displacement, which, given the magnitude of the forces involved, can lead to unpractical and noneconomic anchoring solutions.
An alternative, developed for this Project, has been to identify midline positions to anchor the flowline and let the ends free to expand. This has the beneficial effect of considerably reducing the forces involved and thus allows the use of a more efficient anchoring structure with a Hybrid Foundation.
A Hybrid Foundation is the combination of a skirted shallow foundation (so called mudmat) and pin-piles added at each corner of the mudmat. The adjunction of pin-piles increases the holding capacity of the single skirted mudmat by a factor of about 3, which falls then within the range of the anchoring forces required at midline positions along the flowline.
These anchoring structures are installed simultaneously in-line by the pipelay vessel. Pin-piles can be separately installed by a light construction vessel with the assistance of simple clump-weights. This has a major benefit on the installation sequence and the overall schedule.
The present paper focuses on the selection of the mitigation concept, on geotechnical and structural analyses of the Hybrid Subsea Foundation (HSF), and provides feedback from the recent installation campaign.
This paper describes both the challenges and development of a novel solution involving 3.5-in. diameter coiled tubing (CT) for deepwater pipeline commissioning applications. The work scope required that the complete solution be capable of multiple deployments and recovery operations using a single string of 3.5-in. CT from a floating support vessel. The project began with a detailed analysis of the existing available equipment and tools to determine their suitability and limitations for this application. Factors in this analysis included the limited vessel space available for surface equipment, crane capacity, and the suitability of equipment for working outboard on a vessel. This led to the planning, designing, and sourcing of suitable CT equipment. Trials were performed onshore to optimize the rigup, stackup, vessel layout, and assemblies handling. The combination of pre-operation planning and trials led to confidence in the new tools, work methods, and risk assessments. Because the purpose of the deployment work was to complete the commissioning work on several different marine pipelines and risers, the equipment and work methods had to be easily transferred between vessels. This paper presents and discusses the range of technologies that were developed and successfully applied for the first time globally to complete the project. These include the first fully sealable subsea quick-disconnect for CT, the first pump-through modular clump weight, and the first real-time, high-cycle fatigue (HCF) monitoring system to aid in CT pipe management. The deployment and recovery operations involved a wide range of challenges and led to the development of specific tools and methods for using large-diameter CT equipment. In addition to discussing the design and development of the solution, this paper presents the results and lessons learned from successfully using the large-diameter CT downline solution for deepwater pipeline commissioning applications.
Bottom trawling activities can potentially influence pipeline design substantially. In order to evaluate the conservatism imposed by current standards, such as DNV-RP-F111, it is of interest to further study the interaction between trawl gear and pipelines. This paper presents results from simulating the pullover interaction that takes place when clump weights interfere with subsea pipelines. The nonlinear finite element software SIMLA has been utilized for the simulations. MARINTEK performed model tests for clump weight interference with pipelines on behalf of Statoil for the Kristin field development in 2004. These model tests have been replicated in a full scale SIMLA model, and numerical results are compared with the experimental ones. In addition to simulations of these idealized model test setups, simulations have also been performed for a realistic example flowline both in free span and resting on seabed.