A compliant tower's mass and stiffness characteristics are tuned such that its natural period would be much greater than the period of waves in the extreme design environment. The early development of gravity platforms in the 1970s was driven by the generic requirement to store large volumes of oil and support a heavy topsides in deepwater. The hull of a GBS is made of several tanks that are used to store oil and ballast. The method of installation depends on the weight and the physical dimensions of the jacket and on the capacity of the installation equipment. The platform … Therefore, pile weight is an important part of total structural weight. To simplify installation and hookup at sea, the equipment and facilities are often placed in modules, which may weigh several hundreds to many thousands of tons. 3. It was found that a combination of poor geometry and an inadequate design were the causes of the platform's failure. The modules are completely prefabricated and tested onshore prior to transportation and lifting onto the jacket deck(s) by offshore crane vessels. Launched jackets need to have sufficient reserve buoyancy in order to ensure they float at the end of the launch sequence. 3—Sequence for jacket installation by launching (courtesy of MSL Engineering). All of these structures were partially built in a drydock and then completed afloat in sheltered waters. The base and the tower sections are lattice space structures fabricated from tubular steel members and thus termed the jacket base and the jacket tower sections. However, the development of fields in the future using this technology may be limited, primarily in light of the trend toward subsea wells with long tie-backs and floating production systems. Condeep is a make of gravity-based structure for oil platforms developed by engineer Olav Mo in Hoeyer-Ellefsen and fabricated by Norwegian Contractors in Stavanger, Norway. Bader Diab Naji Tahan, in Handbook of Offshore Engineering, 2005. Jackets with three legs are known as tripods. 2001. The Troll A platform is a Condeep gravity-based structure offshore natural gas platform in the Troll gas field off the west coast of Norway. TYPE OF PLATFORMS (FIXED) s CONCRETE GRAVITY STRUCTURES: – Fixed-bottom structures made from concrete – Heavy and remain in place on the seabed without the need for piles – Used for moderate water depths up to 300 M. – Part construction is made in … Kiewit's expertise in organizing and executing complex slipforming operations was needed on the construction of this offshore, oil-production platform after the original contractor fell behind schedule and over budget. During a cold, sunny, but windy period of 3 days, the QC manager in charge of the production of the concrete for the construction of a gravity base faced a serious problem. Due to the large weight and height of the tower section, it is designed such that it is self-upending after separating from the launch barge and going into the water. The weight of the launch truss normally constitutes a significant part of the jacket weight. Fig. When the possibility of combined tidal stream and swell forces is considered, a high safety factor will be necessary for a satisfactory confidence level, especially for buoyant submerged devices. 6—Topsides modules being lift-installed (courtesy of BP). A typical sequence of steps involved in the installation of a jacket structure by launching is shown in Fig. FPSO – Floating Production, Storage Offloader From the above we shall examine the steel jacket fixed platform in the following sections. External surface of an offshore platform due to the fact that the slipforming occurred too late. Presented at: Long-Span and High-Rise Structures , IABSE Symposium, Kobe, 1998 , … [5] These platforms were also designed for sea access rather than helicopter access, thereby reducing the topsides facilities. Steel Jacket Fixed Platform 2. Some consideration should be given to provide remotely operated valves with manual back-up. Surrey, UK: MSL Engineering Ltd. O’Connor, P., Defranco, S., and Manley, B. A launch barge is a flat top cargo barge equipped with skid beams, a rocker arm, launch winches and a suitable ballasting system. Another type of bottom-supported structure behaves like a fixed structure in a mild environment. The modules are completely pre-fabricated and tested onshore prior to transportation and lifting onto the jacket deck(s) by offshore crane vessels. Minimal Offshore Facilities of the Future. Fig. The jacket base section is transported on and launched off the deck of a launch cargo barge at site. In following the development of the technology related to fixed steel structures and the historic achievements, two additional observations are worthy of note. Section 14.9.4 lists the typical unpiled stability requirements. It can be observed that offshore hookup is minimized because most of the topsides equipment and facilities are commissioned onshore prior to placement on the deck. 2.6. The jacket structure is placed horizontally on a flat-topped barge and towed to site. 1. Figure 18.3. The ballasting permits the skirts to penetrate into the seabed. Historical background on the development of bottom-supported structures is covered in Chapter 1. The failure mechanism was then concluded to be a shear failure that split open several walls in one of the platform shafts, which led to leakage of water which induced the final collapse. On August 23 1991, during a controlled ballasting operation in preparation for deck mating, the Sleipner platform sank. [1] For small structures in shallow water, the pile weight may approach the weight of the jacket structure. Once the towers are constructed and topped off, the whole structure is ballasted down to receive the topsides deck and modules. In Behavior of Offshore Structures. While suction piles were originally developed to provide anchor points for single-point moorings, their use for jacket structures offshore Norway (Europipe 16/11E and Sleipner Vest) has encouraged their wider acceptance. Then, the tower section is transported on the deck of a launch barge and launched into water. Jacket weight cannot exceed the capacity of the tow-out barge. SPE disclaims any and all liability for your use of such content. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. 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