If the lifting was carried out when the concrete of the north face was hard enough, on the south face the concrete would be too hard and stick to the form, so that during the lifting the surface concrete would be torn quite deeply. Built from reinforced concrete, as of 2014, it was the tallest and heaviest structure that has ever been moved to another position, relative to the surface of the Earth, and is among the largest and most complex engineering projects in history. [5] These platforms were also designed for sea access rather than helicopter access, thereby reducing the topsides facilities. In 2000, the 21st edition of API RP 2A was released. Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read, Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro, Concrete gravity based offshore structures. Since that time, more than 1000 functionally similar concrete structures have been built in that area (Norwegian Con-tractors, 1991a). Once offshore, the jacket is lifted off the deck of the barge and lowered down to the seabed. concrete platform for oil and gas production in the Gulf of Mexico was installed in 1950. Required number of tugs, bollard pull and design of the towing attachments. In these cases, the piles are either grouted or welded to connect the piles to the jacket and permit the topside and jacket loads to be transmitted to the piles and into the soil. Historical background on the development of bottom-supported structures is covered in Chapter 1. Hence, the template carries no load from the deck but merely hangs from the top of the piles and provides lateral support to them. Figure 17.5. Figure 14.4. It is a gravity base structure, built in the fashion of typical Condeep platforms which are reinforced concrete structures floating in water up to 300-m deep. Guyed Tower, Delta Tower and other bottom-supported structures that rotate about their base, whenever the lateral excitation forces exceed the predetermined design limit, are defined as compliant structures. 1.4). Because the cost of piling is substantial, an alternative concept that has been developed is the suction pile, or bucket foundation, because its visual appearance is one of an inverted bucket. structure below 4 seconds to avoid resonant behaviour with the waves (period in the order of 4 to 25 seconds. The second observation reflects the industry’s desire to put into practice the lessons learned from the offshore developments that have taken place worldwide. These are also known as monopods. The jacket is lifted off the cargo barge with the lifting slings and lowered into the water until its buoyancy balances its weight. 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. The south face of the circular gravity base was exposed to the sun and protected from the chilly north wind, while the north face was exposed to a quite cold temperature. The launch truss is an integral part of the jacket structure and serves to transfer the weight of the jacket into the skid beams and the rocker arm during the launching operation. Normally the tower section is much larger than the base section. The GBSs are typically trial-ballasted prior to tow to site. Once vertical, the jacket will be lowered and manoeuvred into position often with the guidance of a pre-installed docking pile. The Hibernia Gravity Base Structure is an offshore oil platform on the Hibernia oilfield southeast of St. John's, Newfoundland, Canada.. A 600-kilotonne gravity base structure (GBS) built after the Ocean Ranger disaster, it sits in 80 metres (44 fathoms) of water directly on the floor of the North Atlantic Ocean 315 kilometres (196 mi) off St. John's, Newfoundland at Coordinates Copyright © 2021 Elsevier B.V. or its licensors or contributors. Pierre-Claude Aïtcin, Jean-Martin Lessard, in Developments in the Formulation and Reinforcement of Concrete (Second Edition), 2019. If the slipping of the form was done when the concrete of the south face was hard enough, on the north face the concrete would be too weak and collapse because it had not enough time to set. These compliant structures generate inertia forces due to their motions. 1 is a modern example of a jacket structure designed for operation in 350 ft. of water. As the name implies, concrete gravity-based structures rely on their own weight to resist the lateral environmental loads. Fig. Table 14.1. Once the towers are constructed and topped off, the whole structure is ballasted down to receive the topsides deck and modules. Installation of the Baldpate piles [De Koeijer, et al 1999]. The construction of concrete gravity platforms is altogether different from that employed for template-type structures. Figure 14.1. Once in water, the jacket base section would be upended by the derrick barge assisted by the jacket buoyancy. Often it is only necessary to provide piles through the legs, depending on the environment and soil characteristics. 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. Additional equipment such as flooding valves, umbilicals and pumps are also needed. The topside structures are normally installed at an inshore location by deck mating or any other suitable method. The torn surface had to be repaired at a very high cost (Figure 18.3). From a geotechnical standpoint, the parameters considered in foundation design include the type/extent of contact between platform base and seabed; stability against overturning and sliding; skirt penetration and grouting, to provide lateral sliding resistance and protection from scour; settlement; effects of cyclic loading on the soil; and soil-structure interaction. An examination of the steps in Fig. The template or jacket structure is a steel space frame that supports, above water, a superstructure comprising one or more decks for production equipment and facilities needed to support and maintain production. Masui, Naoki / Yoshida, Iwao / Rustad, Kjell (1998): Application of gravity base structure technology to bridge substructures. 6. [1] For small structures in shallow water, the pile weight may approach the weight of the jacket structure. 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 Sleipner suction pile, for example, has a 45-ft-diameter plate with a 16-ft skirt depth. The modules are completely pre-fabricated and tested onshore prior to transportation and lifting onto the jacket deck(s) by offshore crane vessels. Piles installed through sleeves on the outside of the leg structure are connected to the sleeve by grouting the pile-sleeve annulus. A gravity base uses the same principle as a deadweight anchor, and its effectiveness can be modeled from a free body diagram [18] (See Fig. The jacket is lifted off the cargo barge using one or two cranes. For Weight of the jacket structure has to be less than the safe lift capacity at the construction facility if the jacket is lifted onto the barge rather than skidded. The first concrete gravity-base structure in U.S. waters was installed in 1978 (Hunteman et al., 1979). Therefore, pile weight is an important part of total structural weight. After, the verticality and orientation of the jacket base are achieved, piles are grouted to the pile sleeves. Concrete gravity base Platform 4. 1. This allows economical bottom-founded structures to be designed for water depths, which would not be practical for fixed structures. Once vertical, the tower section, is ballasted to the required float-over draft. Minimal Offshore Facilities of the Future. The lightship displacement of the gravity based structures can be of the order of several hundred thousand tonnes. Jacket has to be designed to float unassisted in the water following launch. where B is the buoyancy force of the anchor, and T is the tensile force in the mooring. A modern, high-energy hammer for 8-ft-diameter piles typically weighs around 160 tons. Subrata Chakrabarti, ... Cuneyt Capanoglu, in Handbook of Offshore Engineering, 2005. Compliancy is achieved using options such as the taut wires connected to heavy chains on seabed or disconnectable pile connections. There is significant interaction between the response characteristics of the jacket structure, its foundation piles, and the soil, such that pile-soil-structure interaction is explicitly catered for in the design recipe for jacket structures. General guidance for design and construction of gravity platforms. The top-hung template requires that moment from lateral wave loads be transmitted up the structure to be resolved into axial pile loads. A Condeep type GBS under construction in Norway. Jackets with three legs are known as tripods. Waves, wind and current cause these structures to deflect, but the magnitude of the dynamic loads is greatly reduced. The completed platform is de-ballasted to a minimum draft for towing and is towed using tug boats to its final location and ballasted onto the seabed. Given its size, several tugs tow the GBS at a very slow speed of 2 knots or less. Figure 14.5. Copy To avoid any slump loss during mixing due to the dry state of the lightweight aggregates, it was decided to keep the coarse lightweight aggregate continuously saturated by sprinkling water on the stockpiles 24 hours per day. [2] This edition reflects good engineering practice, knowledge, and experience gained by the industry over the past five decades. 14.4. This page was last edited on 2 June 2015, at 12:27. This method is used for small jackets, in very shallow water, which are transported on barges in the upright position already pre-rigged for offshore lift and installation by a crane vessel. Each of the Brent Field’s GBS is roughly equivalent in weight to the Empire State Building. The need for heavy hammers to drive large jacket piles has contributed to the development of semisubmersible heavy lift crane barges. Therefore, it has to be pointed out that the existing standards for gravity base foundations need further development especially for the consideration of cyclic loads. 10—Construction of the Troll platform (Photographic Services, Shell Intl., London). 3. The horizontal force from waves consists of drag forces from the kinetic energy of the water and inertia forces from the water-particle accelerations. Successful lift installations of heavy offshore structures require comprehensive and detailed studies involving many engineering and geometrical constraints including geometric configuration of the structure, its weight and centre of gravity, member strength, rigging details, lifting crane vessel and other construction constraints. Today, vessels with a lift capacity up to 14,000 tons exist, allowing most jacket structures to be lift-installed in a cost-effective manner. 2.6. Previous GBS towing distances and duration, Cuneyt Capanoglu, in Handbook of Offshore Engineering, 2005. Bader Diab Naji Tahan, in Handbook of Offshore Engineering, 2005. Another type of bottom-supported structure behaves like a fixed structure in a mild environment. Insulated slip forms have been used successfully during the construction of three large liquefied gas reservoirs of 180,000 m3 in St. John, New Brunswick, Canada. As the size of a jacket structure increases, it is built and transported on a cargo barge in the horizontal position. These platforms consist of a number of buoyancy cells that serve as the floating mechanism. Equivalent practices exist in other countries such as the U.K. and Norway. The piles, after being driven, are cut off above the templates, and the deck is placed on top of the piles. 3—Sequence for jacket installation by launching (courtesy of MSL Engineering). When steel structures are designed for deeper water (in excess of 250 ft), pile-leg grouting is prevalent. For example, the Bullwinkle jacket structure weighed 44,800 tons, and the pile weight was 9,500 tons (i.e., the pile weights are a significant portion of the jacket weight, in this case, nearly a quarter of the structure weight). You must log in to edit PetroWiki. Launch simulation of a self-upending jacket. Drawbacks to this system are the difficulty in ensuring that the grout is adequately placed and of sufficient strength to be counted in the analysis and the additional difficulty in platform removal. Jackets are designed to be either self-upending or upended with the assistance of a crane vessel. SPE disclaims any and all liability for your use of such content. 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. The maximum securing force (W) that a gravity base can exert is given by. A typical sequence of steps involved in the installation of a jacket structure by launching is shown in Fig. Further, these substructures provide the advantageous option of using the gravity base for oil storage. Cambridge, Massachusetts: MIT. Construction of gravity structures is fast and routine and usually cheaper than other foundation types since concrete is not subjected to high price fluctuations like steel [16], [17]. Pile driving is addressed in Section 14.4.2 where a more detailed description is provided. External surface of an offshore platform due to the fact that the slipforming occurred too late. The following methods are the most common for a jacket installation. Completion by slip-forming of all the cellular base walls is undertaken in the harbor, followed by slip-forming of the towers in a continuous process; see Fig. It will consist of a reinforced concrete structure designed to withstand the weight of the topsides, icebergs, and meteorological and oceanographic conditions at the offshore Hebron Project Site. Once located on the seabed, foundation piles secure the structure. The use of MFPs is set to grow over the next decade. The topsides structure is similar to that for steel-jacket structures (i.e., it is either an integrated steel-deck configuration or is of modular construction with a module support frame). We use cookies to help provide and enhance our service and tailor content and ads. 2001. Another advantage of the use of insulated forms when slipforming is that the concrete placed inside the forms hardens in quasi-isotropic and quasi-adiabatic conditions. P.-C. Aïtcin, in Science and Technology of Concrete Admixtures, 2016. This phase is known as the “unpiled stability” phase. Figure 1.4. Offshore Magazine (January). The most common type of offshore structure in service today is the jacket (or template) structure, as illustrated in Fig. Such a structure is designed with the means to behave both as a fixed and as a compliant structure. Larger jackets may require flotation devices to assist in their installation. Grouting procedures for the skirt sleeve-to-pile must recognize that grout placement and inspection will be done remotely. The rocker arms serve to support the jacket weight as it rotates over the barge stern and dives into the water. specific reference to a proposed gravity base structure (GBS) to be located on the sea bed in the Lyell Field of the northern North Sea area, immediately West of the Ninian Field. Single-block upending. Gravity Base Structures (GBS) are composed of giant concrete “legs“ and oil storage cells at the base that support the topsides above the surface of the sea. Figure 18.3. The horizontal force component that can be resisted by a gravity anchor will depend on the fit between the two contact faces. The jacket base section is transported on and launched off the deck of a launch cargo barge at site. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780081028865000177, URL: https://www.sciencedirect.com/science/article/pii/B9780081026168000083, URL: https://www.sciencedirect.com/science/article/pii/B9780080443812500047, URL: https://www.sciencedirect.com/science/article/pii/B9780124104228000017, URL: https://www.sciencedirect.com/science/article/pii/B9780081010181000083, URL: https://www.sciencedirect.com/science/article/pii/B9780081006931000187, URL: https://www.sciencedirect.com/science/article/pii/B9780080443812500217, URL: https://www.sciencedirect.com/science/article/pii/B9780080443812500059, The composition and design of high-strength concrete and ultrahigh-strength concrete, Pierre-Claude Aïtcin, Jean-Martin Lessard, in, Developments in the Formulation and Reinforcement of Concrete (Second Edition), Historical Development of Offshore Structures, Subrata Chakrabarti, ... Cuneyt Capanoglu, in, Design and Analysis of Tall and Complex Structures, Science and Technology of Concrete Admixtures, days, the QC manager in charge of the production of the concrete for the construction of a. Grouting is undertaken to fill any voids under the base. Typically, using a range of standards, the structure is designed to meet the criteria laid down for the ultimate progressive collapse, fatigue, and serviceability limit states. The size and weight of the foundations (from 1500 to 4500 tons) make transport and installation cumbersome, and it is worth noting that the seabed must be prepared by dredging and backfilling material to install the foundation. Table 14.1 summarises the experience in the offshore industry with towing such platforms while Fig. 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 … They are connected to the stern through hinges. Jackets installed in such a configuration are typically less than 50 m tall. the gravity base structure. The flotation devices are subsequently flooded to enable the jacket to sink slowly into its final resting place. gravity base structure). Fig. The process, illustrated in Fig. Small jackets may be lifted in place by a floating crane vessel. Novel and Marginal Field Offshore Structures. Careful examination of the installation process by the geotechnical engineer and integration with other elements of the platform design and construction is necessary. To prevent this type of problem, it is only necessary to isolate the concrete placed between the slip-forms with 50 mm of Styrofoam so that the external temperature no longer influences the hardening conditions of the concrete placed between the forms (Lachemi and Elimov, 2007). Once constructed, this is floated out and moored in a deepwater protected harbor. Gravity Structure Gravity structures (or gravity-based structures as they are often termed) are fixed structures that are held in-place against envi ronmental actions solely by their weight plus that of any contained ballast, together with foundation resistance resulting from … Kurt E. Thomsen, in Offshore Wind (Second Edition), 2014. The ballasting permits the skirts to penetrate into the seabed. Coincidentally, the ballasting of the GBS for deck installation prior to towing to site is often regarded as an effective, full-scale, inshore pressure test prior to offshore installation. The size of the jackets that can be upended with a single crane is limited. Jacket design is an iterative process because a number of design cycles are gone through before achieving the optimal sizing for a particular member to bear these horizontal forces. GBS have been installed in water-depths of up to 300 m. Most gravity based structures are made from concrete although one steel gravity base platform, Maureen, was installed in the North Sea. This may be substantial, e.g., where scouring or settlement allows the gravity anchor to sink below its original installation level, or minimal, e.g., where a square faced gravity anchor is resting on an exposed uneven rock bed. Condeep is an abbreviation for concrete deep water structure. Fig. For a horizontal seabed. The jacket legs and braces transmit environmental and topsides loads into the piles and subsequently into the seabed. Most of the horizontal loads are directly related to the diameter of the tubular members and their locations within the structure. 2—Typical design forces on conventional-jacket structures (courtesy of MSL Engineering). A Kiewit joint venture constructed the concrete gravity base structure and fabricated and installed the topside mechanical works. 8 shows an illustration of a concrete gravity-based structure (GBS). At that time, there was no pipeline infrastructure, and the capacity of heavy lift vessels was only a few thousand tons. A cubic meter of concrete with a dry mass of about 2600 kg will weigh approximately 1600 kg due to its buoyancy in water and can only be used to secure 12,700 N. This makes precast concrete gravity anchors poor holding value for a given volume handled and unsuitable for securing all but the smallest of devices. Force of the towing attachments for fixed structures without appreciable compliancy 2A was released Norwegian Con-tractors 1991a. 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O ’ Connor, P., Defranco, S., and experience gained by the derrick barge and the achievements. Jacket would be connected to the area below, stands on the weight of the anchor, and launching,. The highest frequency of significant wave excitation tow to site barge in with... Minimum Facility Solutions to a derrick barge and the upending slings, while in the horizontal.., in Handbook of offshore installations the buoyancy force of the barge and lowered down to the required draft... Offshore, the jacket weight as it rotates over the barge and launched off the cargo barge the... Typically weighs around 160 tons, although this is no longer disturbed the slipforming.! Pile-Leg grouting is undertaken to fill any voids under the effect of its weight securing (... Assessment Engineering approach is embraced by the jacket ( or template ),. Topsides deck and modules concrete deep water structure two contact faces underkeel and horizontal clearances in the Formulation and of!