A New Lifting System for Installation of Risers in Deeper Water

Transcription

1 Proceedings of the Third (2009) International Deep-Ocean Technology Symposium Beijing, China, June 28-July 1, 2009 Copyright 2009 by The International Society of Offshore and Polar Engineers (ISOPE) ISBN A New Lifting System for Installation of Risers in Deeper Water Xizhao Jiang, Zhigang Li and Ning He Offshore Oil Engineering Co., Ltd., Tianjin, P.R.China Yi Wang Department of Naval Architecture and Ocean Engineering, Dalian University of Technology, Dalian, P.R.China Menglan Duan Offshore Oil/Gas Research Center, China University of Petroleum, Changping, Beijing, P.R.China ABSTRACT A new concept is proposed regarding a lifting system for the installation of risers in deeper water, 1,500 m~3,000 m. This system can also be used for lifting equipment other than risers. Also reviewed are some recent, key methods for the instillation of deepwater risers and related installation analysis methods. In addition, the latest advances on riser installation are described for the development of deepwater oil/gas in the South China Sea. KEY WORDS: Deepwater riser, riser installation, riser lifting equipment. INTRODUCTION With energy needs rapidly increasing for several years now, deepwater oil/gas exploration and exploitation are undoubtedly becoming a trend. In developing the South China Sea offshore oil and gas reserves, China faces the cost-reduction challenge that arises when development moves into deeper water. Riser system technology and its cost are particularly sensitive to any increase in water depth; this is also true of riser installation costs. Current deepwater riser installation technique predominantly consists of lining up the pipes aboard the ship or surface platform, welding, inspecting the pipe using NDT and coating, then installing the risers at the predetermined site. Vessels with special devices are required to install these welded risers, thus incurring high day rates and mobilization costs. This paper reviews the deepwater riser and installation methods currently in practice for steel catenary risers (SCR) around the world, and it presents some achievements of a sub-project of the Chinese National 863 High-Tech Program, Technology Research of Deepwater Riser Installation. This is followed by the presentation of a new concept regarding lifting equipment for the installation of risers in deeper water. DEEPWATER RISER AND INSTALLATION METHODS Deepwater Riser A riser system basically consists of conduits between floaters or platforms on the surface and the subsea facilities (e.g. wellheads, manifolds) at the seabed. There are two kinds of risers: flexible and rigid. A hybrid riser is a mixture of these. In addition, based on the configurations, risers can be separated into the SCR, top tensioned riser (TTR), lazy S riser, steep S riser, lazy wave riser, steep wave riser and others. Since the deepwater riser is a relatively new concept when compared to shallow water risers, the following problems should be thought through carefully during the design and choice of riser type: When riser top tension and reacting forces at floater are high. Deepwater current can induce vortex-induced vibration (VIV) and a re-entry control problem. HP/HT often needs highly reliable technology. Global and local analysis is complex and often coupled with floater motion. Pipe soil interaction is complicated. SCR Installation Methods An SCR consists primarily of a steel pipe string hanging free from the vessel to the seabed to form a simple catenary. The main advantage of the SCR is that steel pipe costs significantly less than flexible pipe, and it is actually flexible in a long length. SCR have been used in the Gulf of Mexico, West Africa, Brazil and Indonesia. They are typically used: with tension leg platforms (Shell Auger TLP, Mars and Ram- Powell TLP, etc.) or Spars (Mardi Gras Transport System, etc.), where heave motions are small; or, with semisubmersibles (Marlim Semi, etc.) or FPSO (Erha and Erha North oil field development, etc.), where the environment is mild. 36

2 SCR are generally installed in one campaign to avoid additional vessel mobilization costs. Various methods of installation have been applied, including J-lay, S-lay (Weustink, 2003) and Reel-lay. However, the J- lay process is currently the prime technique for laying pipelines in very deep water; there, they are handled almost in a vertical direction and pulled under a predetermined high tensile force while being lowered to the bottom using the J-lay method. The technique can reduce the back tensions required to prevent the pipe from overstressing of the sag bend and overbend. Because the vertical space configuration on a J-lay vessel allows for only one pipe-joining station, a fast and reliable pipejoining technique is a prerequisite for the practical use of the J-lay method (Cavicch, 2003). Table 1 lists the main in-service pipeline and riser installation vessels around the world; as can be seen, the J-lay vessels are in the majority. Name of Vessel Company Installation Method Apache Technip Reel-lay DeepBlue Technip J-lay DB50 JRM J-lay Semac EMC S-lay S7000 Saipem J-lay Castoro Sei EMC S-lay Seaway Falcon Stolt Offshore J-lay & Reel-lay Solitaire Allseas S-lay FDS Saipem J-lay Balder Heerema J-lay Skandi Navica Subsea7 Reel-lay DLB Hercules Global S-lay & Reel-lay Lorelay Allseas S-lay Table 1 Installation fleets Typically, SCR installation can be executed by 3 different methods based on the project arrangement (Graaf, 2005): Pre-lay the SCR. Prior to arrival of the facility, the SCR is constructed and then temporarily stored on the seafloor. After arrival of the facility, the SCR is recovered and connected to the facility (Bouwman, 2007). Post-lay the SCR. After arrival of the facility, the pipeline is recovered, and the SCR is constructed and connected to the facility in a continuous operation. Post-construct the SCR. After arrival of the facility, the SCR installation is begun and completed at the facility. Chinese National 863 High-Tech Program for South China Sea (SCS) Oil and Gas Resource Development The SCS is rich in oil and gas resources and is in fact called the second Persian Gulf. But its average depth is also the largest in China. At present, China's bidding for exploration blocks in the SCS has reached a depth ranging from 1500 m to 3000 m. China's offshore oil development started rather late and its practical experience currently lies only at the 200-m water depth. Heeding the urgent need for deepwater oil/gas exploitation in the SCS, a body of national-level research is being carried out both by oil companies and by some other research organizations. Included is the Chinese National 863 Hi-Tech Program, Key Technologies of Deepwater Pipelay; China Offshore Oil Engineering Co. (COOEC) is in charge of this project. Program s Main Target In order to develop the SCS oil and gas resources, a new S-lay crane vessel for the 3000-m water depth, the HYSY201 (Fig. 1), is under construction in Shanghai. Table 2 gives some of HYSY201 s parameters. Parameters Length overall Width of hull Height of hull Speed Pipelay velocity Pipelay range Main crane Auxiliary crane DP system Table 2 HYSY201 parameters HYSY m m 14 m 1.2 knot 5 km/day 6~60 in 4000 t 40 t DP2/3 The main target of the program is to achieve the design and construction capability of a deepwater pipeline based on the new HYSY201. Included is technology research on: Deepwater pipeline design and construction Stringer design and construction Deepwater riser installation Deepwater pipeline monitoring and inspection Tensioner design and construction Welding equipment Some Achievements in Sub-Project of Chinese National 863 High-Tech Program Through a 2-year effort, a study has been made of the aspects of the recent advance in deepwater riser installation, length analysis of the SCR vortex-induced vibration (VIV) suppression device, static and dynamic global analysis for deepwater riser installation (Quintin, 2007), local components analysis, and so on. Here are the main results of our work. Finite element models of the risers were made using the generalpurpose FEA solver ABAQUS for the analysis of deepwater riser installation (Fig. 2). The pipelay process is carried out in good environmental conditions; Table 3 presents the maximum windcondition parameters. We consider the effect of different installation angles in the SCR laying procedure, and the course using the remotely operated vehicle (ROV) pull-in of the SCR to the floater. Further, the RAO motion characteristics of the HYSY201 were used for the dynamic analysis of the deepwater riser installation. Wind speed Significant wave height Wave period (peak) Current speed Table 3 Environmental conditions for pipelay 16 m/s 2.5 m s 2.0 knot The evaluation work was done for the riser joint, such as the bend stiffener for the flexible riser and the flex-joint for the SCR; we conducted the relative analysis based on the global analysis. The main challenge faced during the riser joint design is the simulation of the material nonlinearity and the contact problem. Figs. 3 and 4 present 37

3 some results. SCR installation generally uses strake to minimize VIV. The VIV of marine risers is now analyzed by semi-empirical prediction tools or by computational fluid dynamics (CFD) techniques. We used SHEAR7 and ABAQUS together to calculate the strake length necessary for SCR. The process of transfer from installation vessel to target platform is crucial whatever method is chosen for SCR installation. An installation auxiliary system was designed for extending the function of the HYSY201. Based on these achievements, a deepwater riser installation software system was developed. This software aims to simulate the whole procedure of riser installation, to supply the necessary reference parameters for the installation auxiliary device design and the installation experimental plan. Software functions should include the critical section and curvature analysis during the installation; the force analysis of the installation auxiliary device; riser abandon and retrieval analysis; simulation of the effects of wind, wave, current and platform movement considering the dynamic analysis; the analysis of installation with VIV suppression devices and the installation database system. DESIGN OF DEEPWATER RISER LIFTING SYSTEM Design Basis The HYSY201 is a dynamically positioned, deepwater double-deck pipelay vessel for laying subsea pipelines in water depths to 3,000 m with a central firing line and fixed stinger. The vessel will be suitable for a pipelay speed of 5 km/day. Pipe storage on the top deck will extend to 9,000 t. Pipe handling and transfer will be performed with 2 traveling gantry deck cranes, rollers and conveyors. Fitted on the stern will be a 4000-t fixed and 3500-t revolving heavy-duty offshore crane. The operational area of the vessel at the moment will primarily comprise the East China Sea, South China Sea and South East Asia Sea. The vessel will also be suitable for worldwide service. Referencing the J-lay method (Kopp, 2004) and some projects such as Ormen Lange MEG pipelines installation project (Forbord, 2006), we designed a specialized integrated lifting system for the HYSY201. Fig. 5 shows the concept draft; the lifting system is proposed for the auxiliary installation of risers in deeper water, as well as for the installation of other equipment, such as pipeline end terminations (PLET) rather than risers (Antani, 2008). The system components include: Main frame Decks for welding and transforming Quick connection unit Abandonment and recovery (A&R) wire restraining device Riser restraining device Fixing device for riser Design Considerations The pipes are handled in the horizontal direction with the S-lay vessel, while the pull-in operations of a long riser are handled almost in the vertical direction. In order to assist riser installation as well as to meet the future need of PLET installation (Wolbers, 2003), we used the J-lay method concept for reference. Because the newly designed device will be used for the HYSY201, damage control to the riser, cost and vessel modification must be taken into account. Design considerations include: Ease of connection and disassembly. The A deck of HYSY201 is rich in facilities for the pipelay operation. The riser lifting device must use part of the pipelay area. Because the A&R wire and the welding line are on 2 decks, the crane on the vessel must be capable of being used for assistance. It must be possible to lead the A&R wire from the central firing to the position where the system is placed. A transition forge ring face is used for temporarily fixing the pipeline to the fixing device. The capability of restraining the movement of the A&R wire. The capability of restraining the movement of the riser. Meeting the requirements of different riser diameters. Meeting the requirements of PLET installation. Component Design As can be seen from Fig. 6, the A deck of the HYSY201 is full of facilities and rooms. The 400T A&R winch is at the bow, while the main crane is at the poop. For minimum vessel modification, we placed the lifting system at the lift side pipeline yard, where it is originally used for laying the approximately 400-t pipeline. A quick connection unit (Fig. 7) is designed to meet the requirements forfast connecting and disassembling. The quick connection unit is made up of 3 parts: an upper component connected to the lifting device, down components connected to the vessel, and a middle component with rubber to minimize the impact force. In the riser s recovery from seabed operation and the lowering operation, the movement of A&R wire and the movement of the riser need to be restrained. Two devices were designed. One device, with a hydraulic drive cylinder, was designed for the need of restraining the A&R wire movement; this (Fig. 8) is drawn back when the top of the riser is above sea level, so as to avoid possible collapse between the riser and the A&R wire restraining device. Another device, with a hydraulic drive cylinder and pulleys, was designed to restrain riser movement. The riser restraining device (Fig. 9) is openable when the riser is moving to the fixing device, so as to avoid possible collapse between the riser and the riser restraining device. The riser is to be fixed during welding and other operations. An openable fixing device (Fig. 10) was designed. The riser angle must be considered in the device design, and the openable device is replaceable in order to meet the need for different riser diameters. PLET Installation Process Before operation startup, the PLET has been transported to the HYSY201. The A&R wire is lowered to the pipeline recovery sling on the seabed and hooked in, assisted by a ROV. Then the pipeline is recovered to the deck of the riser lifting system. The main crane of the HYSY201 is used for assistance to transform the pipeline into a riser fixing device. The temporary head of the pipeline will be removed when the pipeline is fixed, and the pipeline end is prepared for the PLET installation. Then the main crane is used to upend the PLET and transform it into the supporting tower and riser fixing device of the riser lifting system. This will eliminate movement due to wind and vessel motions, which would result in exceeding the allowable strain on the pipe. 38

4 After the pipeline is welded onto the PLET, the weld is inspected and field joint coating is applied. The PLET is lifted with the pipeline by the main crane back to the deck, where the A&R wire is placed. Once the force is transferred to the A&R wire, the A&R winch will lower the PLET onto the seabed CONCLUSIONS As the petroleum industry moves into deeper waters, installation of deepwater risers will meet many tougher challenges. The CNOOC is making a great effort to develop technologies and equipment for deepwater oil/gas drilling and production in the South China Sea. This endeavor in deepwater riser installation has been one of the recent advances in deepwater engineering. The proposed riser lifting system in deeper water will be in operation in ACKNOWLEDGEMENT This project is supported by the China National 863 High-Tech Program (Grant No: 2006AA09A105). REFERENCES Antani, JK, and Dick, WT (2008). "Design, Fabrication and Installation of the Neptune Export Lateral PLETs," Proc Offshore Tech Conf, Houston, Paper OTC Bouwman, J (2007). Installation Challenges with Lifting and Pull-in of the 20-inch SCR, Proc Offshore Tech Conf, Paper OTC 19061, Houston. Cavicch, M (2003). "J-Lay Installation Lessons Learned," Proc Offshore Tech Conf, Paper OTC 15333, Houston. Forbord, PK, and Myklebost, L (2006). "Deep Water Pipelay in Harsh Environment," Proc D.O.T XVIII Conf, Houston. Graaf, van der, J, Wolbers, D, and Boerkamp, P (2005). Field Experience with the Construction of Large Diameter Steel Catenary Risers in Deep Water, Proc Offshore Tech Conf, Paper OTC 17524, Houston. Kopp, F, and Light, BD (2004). Design and Installation of the Na Kika Export Pipelines, Flowlines and Risers, Proc Offshore Tech Conf, Paper OTC 16703, Houston. Quintin, H (2007). "Experience with the Design and Installation of Steel Export Lines for Deep Water Projects," Proc 17th Int Offshore and Polar Eng Conf, ISOPE, Lisbon, Vol 2, pp Wolbers, D, and Hovinga, R (2003). Installation of Deepwater Pipelines with Sled Assemblies Using New J-Lay System of DCV Balder, Proc Offshore Tech Conf, Paper OTC 15336, Houston. Weustink, OWA (2003). "Bombax 48-inch Pipeline Installation," Proc Offshore Tech Conf, Paper OTC 19688, Houston. 39

5 .Fig. 1 General arrangement of the HYSY201 Fig. 2 Riser stress distribution on stinger of pipelay vessel during installation Fig. 3 Bend stiffener analysis Fig. 4 Flex-joint analysis Fig. 5 Concept draft of lifting device design for the HYSY201 40

6 Main crane A&R winch Lifting system.fig. 6 General arrangement of A deck Fig. 7 Concept draft of quick connection unit Fig. 8 Concept draft of A&R wire restraining device 41

7 Fig. 9 Concept draft of riser restraining device Fig. 10 Concept of riser fixing device 42