A new concept Spar-FPSO is proposed for deepwater oil field development integrating the advantages of the deep-draft Spar concept and for oil storage. Unlike conventional ship-shaped FPSOs, the Spar FPSO uses the oil-over-water storage method or oil-water displacement technology for oil storage, which is similar to that used in the fixed gravity-based platforms.
In order to investigate the VIM’s influence to mooring line tension and the platform motion characters, towing model test and wave basin model test are done. Based on model test conclusions, some corrections are added to numerical model, and perform a good consistency between numerical results and model test values. And from a full scale numerical stimulation, the VIM‘s effect on the mooring tension and Spar-FPSO’s offset are discussed.
A simple mooring line fatigue sensitivity analysis about VIM’s influence is done by using API simple summation method. VIM phenomenon lead to a more complex mooring tension distribution, higher offset motion and more serious mooring line fatigue problem. In order to better understand VIM character, more studies are needed.
Cylindrical structures exposed to a current create alternating eddies, or vortices, at a regular period. Figure.1 show how these eddies appear in the downstream wake of a cylinder. When the vortex shedding period close to the natural period of platform, “lock-in” phenomenon may appeared. The VIM may lead two aspects to mooring system of Spar1:
Firstly, inline pulsing drag force and transverse lift force would increase mooring line tension load;
Secondly, the long period response would increase mooring line fatigue damage.
With Spar platform taken into operation since 1990s, many studies are done on Spar VIM. By monitoring, the Genesis Spar has experience as large as 40% its diameter VIM, which is two times compared with design value 17% diameter (David W. Smith, 2004)2. Mehernosh Irani(2004) 3 described Spar VIM model test method , given a conclusion that model test is an effective method to analysis Spar VIM. By towing model test, uniform current flow could be simulated approximately. Un-uniform current flow could be simulated by using wave basin model test. Radbound Van Dijk(2003) 4 describe a VIM model test of Truss Spar and compared platform VIM behavior with and without strake, found the strake could reduce VIM motion amplitude effectively. Weiwen Zhao (2014) 5 using CFD analysis Spar’ VIM under uniform current flow, shows a good consistency with towing model test results.
Jameel, Mohammed (Department of Civil Engineering, University of Malaya) | Khaleel, M. (Department of Civil Engineering, University of Malaya) | Saiful Islam, A.B.M. (Department of Civil Engineering, University of Malaya) | Ahmad, Suhail (Department of Applied Mechanics, Indian Institute of Technology Delhi)
A reliable mooring system is a critical aspect where survivability is considered. Total loss of a structure can occur during mooring system failures. With the advancements of the next generation circular hull shape FPSOs; Satellite Service Platform SSP320 Plus has the ability to utilize a spread mooring design that can be arranged to achieve the most cost effective and reliable design compared to a traditional ship shape FPSO. An additional factor with these increasingly large floaters that have a rectangular hull design is the gyration distance from the tipping point, which generates a significant larger moment than on a circular hull form. Thus, on a ship shape vessel, the mooring spread has limited structural real estate to sea fasten its winches and chain devices.
SSP320 Plus platform's new circular hull design provides better stability with the capability to accommodate a dry tree riser system with minimal yaw excitation whereas traditional ship-shape FPSOs motion varies considerably from head to beam seas.
Torpedo, suction pile and suction embedded plate anchor (SEPLA) have been considered for the permanent mooring system that will be installed in regions off the coast of Brazil. Torpedo pile anchor tends to be favored for these locations however the three anchors mentioned provide different advantages and cost values.
The study also focused on a pure technical evaluation of the influence to "peak shave?? high loading forces when the sea state reaches an extreme event by introducing thruster assist positioning, which can be favorable for an omni-directional hull shape. This results in installation of fewer mooring lines and introduces a higher safety contingency thus giving the mooring system a more cost effective design and the ability to survive extreme events with minimal offsets.
Model tests were conducted in LabOceano, Brazil, with MARIN (Maritime Research Institute) and Oceanica Offshore. Tests were executed for three different loading conditions, ballast, fully loaded and 50% loaded cargo. These tests confirm that the circular shaped hull FPSO response with a larger natural period and hydrodynamic responses similar to a SPAR platform. To further design and analyze a mooring system to meet the design standards, a parametric model was created and analyzed within AQWA. AQWA provided the ability to carry out a frequency domain as well as time domain dynamic analysis of several different mooring line configurations considering a variety of global environmental conditions.
Mooring design results from this extensive study confirm that the mooring materials are well within acceptable market parameters and the mooring systems can be adapted/flexible to allow a variety of services and applications for deep and ultra deep waters.
Jameel, Mohammed (Department of Civil Engineering, University of Malaya) | Saiful Islam, A.B.M. (Department of Civil Engineering, University of Malaya) | Jumaat, Mohd Zamin (Department of Civil Engineering, University of Malaya) | Ahmad, Suhail (Department of Applied Mechanics, Indian Institute of Technology Delhi (IIT Delhi))
A floating platform for arctic regions is required to break ice and withstand high ice loads, be disconnected and towed away in the event of approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and provide large quantities of utility storage. Additionally the platform should provide low motion response to storm and ice loads to maximize the operational uptime and enable the use of current state-of-the-art riser systems.
This paper presents the details of a Spar platform that has been configured to satisfy all requirements for Arctic operation. The paper describes a number of key features that are specifically designed to reduce ice loads on the hull and to allow ice floes to break around the hull without damaging the hull, topsides, mooring or risers, while maintaining the characteristic low motion response to storm environments. The paper also describes the system for disconnecting and reconnecting the moorings and risers in response to approaching large icebergs.
This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 20885, "Perdido Development Project - Spar and Moorings," by Curtis Lohr and Keith Smith, Shell International Exploration and Production, prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed.
The Arctic is the next frontier for oil and gas production, and it will offer new challenges for engineers who must design safe and efficient systems to operate under new environments. Some designs will be based on existing ones modified for these new conditions. In this paper, two floater designs, a Spar and Single Column Floater (SCF), are evaluated for deployment in an arctic environment. The floaters are assumed to support identical topsides and riser payloads and to be subjected to the same environments composed of level ice sheets and ice ridges, wind, waves and currents. Hull steel weights and mooring systems are similar for both designs. The comparison is based on general arrangements and global performance comparing motions responses and moorings loads. Results show that the motion global performance of the SCF is marginally better than the Spar. The ice breaking cone, used on both designs, shows unacceptable heave response on the hulls, requiring them to change drafts depending on whether the environments present ice cover or open-water conditions.