Marine ice floating platform and method of operation

 

The invention relates to the field of construction of offshore marine structures designed for drilling and/or production of oil or gas in the deepwater areas of the ice period. Ice-resistant platform (PL) has a support base in the form of floating columns (PC) with buoyancy compartments and maneuverable ballast tanks (BC) and permeable bottom, which posted solid ballast. PL anchored by a system of inclined anchor links (YAS), located, for example, in the star order. PC has an additional system of sagging heavy chains attached to the eyebolts its lower part, and the other ends of the piles at the bottom of the sea, and the length of the chain exceeds the maximum possible removal of the rings from the bottom of the sea. A method of operating LP includes positioning PL, tension regulation YAS in accordance with a given draught and maintaining the vertical position of the PC. When sea level rise (MIND) take water ballast (EB) in terms of BC, and when the lower MIND is removed WB, regulate the operation with BC so as to minimize the resulting inclination PC. Draught PL and tension YAS change depending on seasonal conditions so that if the ice conditions will reduce sediment and uvelichivaiut sediment and reduce FE and tension YAS, what WB are taking in BC. The invention provides for the maintenance of optimal production platform at sea state and ice effects. 2 C. p. F.-ly, 3 ill.

The invention relates to the field of construction of offshore marine structures designed for drilling and/or production of oil or gas in deepwater offshore fields in areas of the ice age.

Known ice-resistant offshore structures (D. A. Mirzoev, "oil and Gas resistant structures shallow shelf", - M.: VNIIEM, 1992, page 15, 26 or So Dawson, "Design of offshore structures", L., Shipbuilding, 1986), installed on the bottom of the sea. Such structures can withstand the impact of ice fields, giving them the power to the ground, but at a depth of more than 60-80 m platform of this type become cumbersome and bulky, and their cost increases in cubic degree from the depths of the sea.

Also known are not intended for operation in ice conditions on a floating platform based on tension relationships (foreign terminology TLP), anchored gravitational or pile anchors (Recommended Practice for Planning, Designing and Constructing Tension Leg Platforms, API RP 2T, American Petroleum Institute, 1997, S. 3, 12-28, 55). These Platini and great depths of the sea, and classifying their characteristic is that anchor ties are strained by excess buoyancy of the hull. The specified type of platforms connected to ground only through the bottom of the anchor, and their stability is determined by the excess buoyancy providing a tension ties.

Closest to the proposed decision of a kind specified type platforms platform type Spar (J. Kuuri, T. Lehtinen, J. Miettinen, Aker Rauma Offshore Ltd, Neptune Project: Spar Hull and Mooring System Design and Fabrication, Offshore Technology Conference, OTC 8384, Houston, 1997, S. 2-5 and J. E. Halkyard, J. Murray "Spar As a Production Platform in the Arctic Environment", Proceedings of the Third International conference "Development of the Arctic seas of Russia" RAO'97, S. - Petersburg, 1997, S. 25, 26), adopted for the prototype. Floating anchored platform - prototype (see Fig.1 and 2) has to support the upper structure 1 floating body in the form of a vertically extended column 2, which includes an opaque portion with buoyancy compartments 3 and durable maneuverable ballast tanks 4, and permeable part 5 with elastic ballast tank at the bottom. Dry buoyancy compartments 3 tiers provide buoyancy and stability of the platform as floating structures in operational working position of the platform, and maneuverable ballast tank 4, razadyne precipitation platform and its vertical position when the sea level changes or changing the weight of the load platform. For a system of mooring the platform (see Fig. 2) the characteristic slanted anchor connection 6 placed radially in the star order, going from the hawse 7 in the column to the bottom of pile anchors 8. Sloping communications are designed to hold the platform in ice conditions over the wells to move the keel pad 9 column 2 from external influences (including ice) did not exceed the allowable use of drilling and production risers 10. Such platforms are installed at relatively large depths of 300 m and more) easily withstand the rough seas, having a small amplitude of pitching due to the substantial differences in the period of natural oscillations and periods of the waves.

However, this construction is not fundamentally can equally well to resist ice and wave loads. Confrontation ice load requires a large stiffness of the mooring system and a strong initial tension ties in order to avoid large horizontal displacement of the platform in the process of choosing a slack ties. On the other hand, moderate oscillations of the platform when the storm is only possible with the weakening of the ties that guarantee the lowest natural frequency of the translational oscillations of the platform outside the OS is I, and there are abrupt jumps in relationships, leading to excess tension. The same phenomenon holds for the angular oscillations: a large stability platform, created to prevent large inclinations from overturning moment from the effects of ice on the level of the waterline increases the natural frequencies of the angular fluctuations and brings it to the frequencies of excitement (with the same negative consequences). Thus, the desire to reduce the amplitude of the angular oscillation of the platform from the sea leads to the need to reduce its initial stability.

In the proposed framework specified the contradiction is resolved through the use of managed maneuverable ballast tanks to compensate for changes in seasonal conditions and input into the system design heavy chains hanging from the lower part of the column.

The proposed structure is illustrated in Fig.3.

In Fig. 3 shows a General view of the platform in operational working position. The platform consists of the upper structure 1 (modules for various purposes, rig etc), floating substructure in the form of columns 2, including impermeable part: agile ballast tank 3, useast platform in operational working position of the platform, and maneuverable ballast tanks 3 contain variable amount of ballast water. Water ballast can be removed or be taken in maneuvering the tank when the control valve from the control station. Top (traditional) the mooring system includes hawse holes 6 on the column, anchor links 7 and bottom anchors 8 (preferably of pile type). The lower the mooring system is a system of circuits includes eyebolts 9 on the lower part of the column, severe sagging of the chain 10 and piles 11. The weight of chains is added to the weight of solid ballast. The length of the circuit 10 exceeds the distance from the eye 9 to the bottom of the sea by an amount greater amounts possible in this area of the sea level change (caused, for example, tide and/or storm surge) and possible changes in precipitation (i.e., the magnitude of the maximum possible removal of the rings from the bottom of the sea) so far the links (links) circuits when any possible sediment lying on the bottom, and the ends to keep the location in the plan attached to the piles. The tension as the top links 7 and circuits 10 and sediment structures can be adjusted by filling-draining maneuverable ballast tanks 3 when you install the platform and in the process of operation depending on the weight load, external services is in terms of clean water and lack of strong sea waves (so that is, outside of extreme conditions) in terms of 3 tanks hold certain average amount of ballast water, maintaining the nominal settling column 2 and the average tension anchor links 7 and chains 10. When sea-level change (e.g., tide-low tide) or variations of the weight of the load platform support given draught of columns 2 through the reception and removal of water from maneuverable tanks, thereby preserving the initial tension of the ties and chains. When experiencing extreme ice conditions (when the sea, respectively, no) water ballast removed from maneuverable tanks 3, increasing the excess buoyancy of the column, anchor links 7 and circuit 10 upholstered, reaching necessary to withstand the ice initial tension, while the sediment column is slightly reduced. In extreme storm conditions (when the ice is, accordingly, no), on the contrary, water ballast, accept, reducing the excess buoyancy of the column, sediment increases slightly, the links 7 and circuit 10 are attenuated; the amplitude of pitching and effort in the relationship decreases. As shown by calculations and computer modeling, tension as anchor links and chains are very sensitive to variations in precipitation Plaine precipitation (little impact on the day-to-day operation of the platform) significantly increases its stability and security.

The primary role of the sagging of the chains is that they provide additional stabilizing in the vertical direction "gidropony" effect: when you receive a ballast in maneuvering the tank 4 and pritoplennye platform additional chain links lie on the bottom, making it easier to column 2, and when afloat, on the contrary, rise from the bottom, increasing the weight of the column and preventing the ascent. The effect is equivalent to increasing the area of the existing waterline, preventing the inclination and peoplenew platform from exposure to ice, but without negative consequences, such as increasing ice and wave loads due to the increased size of the waterline. The same effect helps to increase stability and reduce the inclinations of the platform from the ice load by increasing the tension of the chains on the side of the column opposite to the action of ice loads. This method of increasing stability does not lead to the above mentioned negative consequences in the form of increased external loads.

The positive effect from the use of agile ballast tanks 4 together with chains is evident in the fact that when you remove water from a maneuverable tanks chain tightened, and there is an additional vosstanavlivatj conditions. On the contrary, in storm conditions, when water ballast accept maneuverable tanks, the stability of the platform is reduced, increasing its own period of angular oscillations, which contributes to umerenuiu pitching and eliminate jerks anchor links.

Thus, the proposed design allows you to achieve a new result by combining (previously unattainable) the following two qualities necessary to ensure the sustainability of floating marine ice-resistant platforms: 1) the counter of the ice load, 2) Umilenie movements from the effects of rough seas and eliminating jerks anchor links by fixing structure as in the upper and in the lower part of the body (chain), and due to the adjustable buoyancy of the hull and pull the anchor links of the upper and lower systems.

The method of operation of the construction is based on the ability of the proposed design of a floating platform. Closest to the proposed method of operation the method of operation of the platform type TLP-SPAR (R. Glanville, J. E. Halkyard, R. L. Davies, A. Steen, F. Frimm, Deep Oil Technology, Inc., Neptune Project: Spar History and Design Considerations, Offshore Technology Conference, OTC 8382, Houston, 1997, S. 1-4, 10, 11), adopted for the prototype. According to the method prototype in the operation of the platform (see Fig.1 and 2) support the th 6. In the case of sea level rise (tide, storm surge) or operational reduce the weight of the load platform take water ballast in the ballast tank 3, and during the lowering of sea level or weighting platform remove ballast handling operations with ballast tanks 3, divided on the sides of the column so as to minimize the resulting inclination of the column (including eccentricity variables cargo). During ballast operations tension in relationships 6 strive to keep constant.

However, as mentioned above, the persistence of the initial tension ties cannot provide confrontation ice and wave loads. Confrontation ice load requires a large stiffness of the mooring system and a strong initial tension ties. On the other hand, moderate oscillations of the platform when the storm is only possible with the weakening of the ties that guarantee the lowest natural frequency of the translational and angular oscillations of the platform; otherwise, inevitably followed by resonance "separation" of the structure.

In the proposed method (see Fig.3) the difficulty is eliminated through the use of collaboration maneuverable ballast zakreplena ends of the piles 11, are, for example, radially in the star order. Due to this arrangement of circuits column 2 is positioned exactly above the place of installation and saves the upright position due to the tension caused by the weight of chains. A draft of the structure during operation of the platform regulate the admission removing ballast maneuverable tank 3 when the stabilizing influence of the chains, with stability decreasing/increasing precipitation platform increases/decreases due to removal/reception weight on top (remove/reception of ballast maneuverable tanks) while receiving/removing weight at the bottom (lifting/lowering chain links with/on ground).

Thus, in operation a set of technical means "maneuverable tank + chain" is used to adapt the platform to external conditions. To purchase quality ledostojkoj platform (missing when using the prototype method) in the event of extreme ice conditions, water ballast is removed from maneuverable tanks, increasing the excess buoyancy, anchor links and chains upholstered, reaching necessary to withstand the ice initial tension, while sediment platform slightly reduced the number increases, communications and chain slackens; the amplitude of pitching and effort in the relationship decreases. Additional tension ties jacks, winches, etc. are not required.

The proposed construction and method of use enables, firstly, sufficient ledostojkoj platform, second, the reduced sensitivity of the platform to the effects of rough seas. Changes to operational precipitation platform with minor and do not affect the process of mining and drilling.

Claims

1. Marine ice floating platform having a support base in the form of floating columns managed maneuverable ballast tanks and mooring system with inclined anchor links, characterized in that the floating column connected to the bottom of the sea through a system of sagging heavy chains attached to the eyebolts in its lower part, and the other ends to the pile on the bottom of the sea, and the length of the chain exceeds the maximum possible removal of the rings from the bottom of the sea.

2. A method of operating a marine ice floating platform, in which position the platform, adjust the tension anchor links in accordance with a given draft, support veracruze platform take water ballast in maneuvering ballast tanks, and during the lowering of sea level or weighting platform remove ballast handling operations with ballast tanks, so as to minimize the resulting inclination of the column, characterized in that a draft of the platform and tension anchor links change depending on seasonal conditions so that if the ice conditions will reduce sediment and increase the excess buoyancy and tension anchor links, for which water ballast removed from agile ballast tanks, and storm conditions increase the draught and reduce excess buoyancy and tension anchor links, for which water ballast accept maneuverable in ballast tanks.

 

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