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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.
The Huizhou oil field is located at the Pearl River mouth in the continental-shelf region of the South China Sea, with an average water depth of approximately 117 m. The oil field's main facilities include eight fixed-jacket platforms, two subsea-production wellheads (HZ32-5 and HZ26-1N), and one floating production, storage, and offloading (FPSO) vessel (Nanhai Faxian). Figure 1 illustrates the general layout of the field. The peak daily oil production is approximately 70,000 BOPD. In September 2009, after a strong typhoon (Koppu) passed over this oil field, the FPSO vessel's permanent mooring system was seriously damaged. All production risers connected to the FPSO vessel's turret were ruptured, and production was forced to shut down.
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).
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.
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.
Riserless Dual Gradient Drilling (DGD) using a specialized subsea pump placed on the seafloor during top hole drilling has been widely used on offshore subsea wells prior to installing the blow out preventer (BOP). Riserless DGD systems, kown as riserless mud recovery (RMR), have been developed to allow riserless sections to be drilled with weighted mud while taking returns back to surface. This allows the operator to set surface casing strings deeper, thereby reducing the total number of liners/casing strings in the well.
This paper addresses the deepest RMR operation on the Norwegian Continental Shelf to date. The water depth was 854m and the 26" hole section was successfully drilled to 1972mMD (1913mTVD). The riserless mud recovery system enabled the 20" shoe to be set at a sufficient depth to allow elimination of the 16" liner, thereby reducing casing strings, cost, well complexity and most importantly setting up the 13-5/8" string cementation for success. This was mission critical from a well integrity perspective in the context of a big bore 9-5/8" upper completion. Following the successful drilling of the 26", the 20" casing was installed and cemented. Foam cement was pumped using the riserless mud recovery system in cuttings transfer mode to prevent accumulation of returned cement at the well head. The 20" casing was successfully tested after installing the BOP and marine riser.
The paper describes the riserless mud recovery equipment and the planning of the well, plus the engineering of a multi-stage subsea pump and the subsequent seabed deployment in order to drill the longest and deepest 26" section on the field. A 26" directional BHA with a 1.30sg surface mud weight (1.18sg downhole mud weight) KCL glycol mud at flow rates of up to 4800 lpm was used to drill to TD. At TD the well was circulated at a lower rate to 1.38sg surface mud weight at 3200lpm to provide trip margin over the effective mud density required for wellbore stability.
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.
Infield umbilical is the extension of the main umbilical, and provides control to remote wells or tie-ins of new subsea developments. The umbilical termination heads (UTH) are typically much heavier than normal cobra heads to accommodate the umbilical self weight during installation, hence it requires different installation techniques. In PY 35-2/35-1 project, the UTH installation was foreseen as more challenging due to a relatively new concept of the UTH was used. The UTHs contain a compliant section between multiple quick connect (MQC) stab plate and armor pot, with an intention of reducing the torsional and bending resistance during subsea connection. This arrangement may also introduce potential risks to umbilical deck handling and overboarding. This paper is to summarize the concerns during the installation engineering phase, adopted risk mitigation actions, and offshore installation lessons learnt. First, the infield umbilical system is described, including details of the UTH compliant section. Second, the main concerns for handling are also listed and discussed. And the risk mitigation actions are discussed. Also it was decided to carry out a UTH handling test to quantity the UTH behavior during installation. The UTH handling test procedures and results are then highlighted. The testing results disclosed good insights to the compliant section behavior, revealed the UTH handling risks are within controllable level. Third, offshore installation and lessons learnt are summarized. During the installation the UTH behavior was well controlled, while additional contingency plans could be developed to improve the subsea connection and release the 2nd end umbilical twist. Lastly, conclusions were drawn. All infield umbilicals were installed successfully offshore, which indicated that the techniques adopted in this project are effective for risk management. And the presented experience and knowledge could be beneficial to other similar projects as well.
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 pull-over 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.