Classifications

• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
  • E21B41/005—Waste disposal systems
  • E21B41/0071—Adaptation of flares, e.g. arrangements of flares in offshore installations
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
  • E21B41/005—Waste disposal systems
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
  • E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations

Definitions

• the present invention relates to a method for pressure relief in a production process on a platform offshore.
• the invention also comprises a device for a pressure-relief system.
• zone-divided pressure- relief In the case of any leakage of gas, it must be certain that no gas can travel from one zone to another, and this makes great demands on the constructional design. Moreover, a zone-divided pressure- relief will require a much more complicated pressure-relief sys ⁇ tem. The method of zone-divided pressure relief can therefore be considered a far from satisfactory solution, both economically but perhaps even more security-wise, since the total time of depressurization will be considerably extended.
• the objective of the present invention is to achieve a method of depressurization of a production process on a platform offshore, where the need for a conventional flare is eliminated or where the length of the flare boom can be considerably reduced, and where the total length of time of depressurization can be kept as short as possible.
• the invention is achieved by a method which is characterized in that the pressure-relief medium, mainly gas, is fully or partly led to release underwater.
• the invention also comprises a device for putting the method into practice.
• the invention will also be of great importance on floating pro ⁇ duction platforms, where the size of the flare boom plays a critical role in the stability of the platform.
• fig. 1 shows a basic embodiment of the invention
• fig. 2a-2c show schematic embodiments of the pressure-relief concept according to the invention
• fig. 3 shows an embodiment of the invention
• fig. 4 a-e show various embodiments with gas-release at various depths.
• a fixed platform 10 is shown, with an indicated under ⁇ water gas-release system 13, indicated in the form of a pipe, and where the gas is released under water at a considerable depth beneath the surface of the sea 12.
• Tests have shown that a dis ⁇ charge of gas at a depth of 100 metres, will spread on the sur-
• the gas-release system consists there ⁇ fore of a combination which comprises a conventional pressure- relief system with a flare and a gas-release system under water.
• a conventional pressure- relief system with a flare
• a gas-release system under water.
• the flare can be dimensioned to receive considerably smaller amounts of gas, and can therefore be built shorter and with a much lower weight.
• such a system will be particularly advantageous, since it will be possible to build the platform deck smaller and cheaper.
• a schematic embodiment of such a "double release system” is illustrated more closely in fig.
• FIG. 2a which shows a gas-release system according to the invention where gas from sources of high pressure is led by way of a high- pressure tank 21 and a high-pressure line 22 to discharge under water.
• the high-pressure line 22 comprises a branch or side-line 24 a which leads gas to a conventional flare 25.
• the gas flow in the side-line 24 a is limited by a choke 23 a.
• Gas with low pres ⁇ sure, is led by way of a low-pressure tank 26 and a separate line 27 to the flare 25.
• a separate loop 28 to lead off gas with atmospheric pressure is also indicated.
• Figure 2b indi ⁇ cates schematically an alternative embodiment of a double de ⁇ pressurization system where high-pressure gas, for example from underwater sources, is led through a header line 22 to release under water.
• high-pressure gas for example from underwater sources
• a header line 22 instead of a separate side-line 24 from the high- pressure line to the flare, a side-line 24b is arranged, with a choke 23b which is connected to the low-pressure line 27.
• This solution is simple and functionally safe and the choke opening 23b can be chosen according to the capacity of the flare 25.
• Figure 2c shows an embodiment where two side-lines 24b, 24c are used, which side-lines 24b, 24c are parallel to each other, be ⁇ tween the high-pressure and low-pressure lines 22, 27, a side ⁇ line 24b with choke 23b corresponding to fig. 2b, and a side-line 24c which is, in addition to a choke 23c, equipped with a valve 29, preferably a time-regulated valve.
• a valve 29 preferably a time-regulated valve.
• Fig. 3 shows a preferred embodiment of a "double pressure-relief system" on a platform 10.
• the pressure-relief system comprises a header system 31 from each pressure-relief group.
• the collective pipe system 31 is extended down to the sea-bed for discharge via an underwater gas-release system 13.
• the header system 31 is connected with a side pipe 33 which leads along a boom 34 to a conventional flare 25.
• the side pipe 33 comprises a choke or valve for regulating the flow of gas.
• the flow through the choke will be a function of the upstream pressure from the system and the opening of the choke. If a valve is used, it can be time-regulated. In the figure, only one header system is indicated on the deck. Some equipment, for example some types of compressor, are sensitive to back pressure in the header system 31, and in practice, a separate pressure-relief loop connected directly to a conventional flare would be required for such equipment. It must however, be pointed out that the amount of gas which has to be pressure-relieved with such equipment is relatively small.
• the underwater gas-release system 13 which is a collective term for the pressure-relief system which comprises the extension from the header system 31 and down to the discharge site or sites, extends in the upper part inside the shaft of the platform 10 ' and through the wall of the shaft and further down the outside of the platform's shaft at considerable distance from the surface of the sea.
• the gas from the various pressure-relief groups is, in a conventional system, collected with a header system which ends up in a knock-out drum and a flare 25.
• the requirements today are that most sources can be pressure-relieved to about 7 bars within a certain period of time.
• the equipment In the case of discharge under water, the equipment will be depressurized to the static pressure which prevails at the site of discharge and fur ⁇ ther pressure-relief will take place through a conventional flare with a reduced boom length. It is desirable to relieve as much of the gas as possible under water, so that the length of the flare boom can be as short as possible.
• the gas-release system under water is provided with several points of discharge located at various depths.
• Figures 4 a-e show schemati ⁇ cally several constructive embodiments of such a system, and each embodiment will be more closely described in the following.
• Fig. 4a shows a platform 10 which is founded on the sea-bed 11 and comprises a schematically shown underwater gas-release system which comprises three points of discharge 45a, 45b, 45c, at three different levels.
• the discharge points of the gas 45a, 45b, 45c are situated at a horizontal distance from the platform 10.
• the underwater line 13, which is secured to, and extends downwards alongside the platform shaft, is produced pre ⁇ ferably of rigid corrosion-resistant material, for example steel.
• Flexible hoses, 48a, 48b, 48c which lead out to the points of discharge 45a, 45b, 45c, are attached to the line 13.
• hose-ends are attached to a chain arrangement 49 which at it's lower end is secured to the sea-bed 11, while it's upper end is secured to a buoyancy element 50.
• the arrange ⁇ ment is kept secure by way of guy ropes 51 secured to the seabed 11 and possibly to the platform 10.
• the flexible hoses 48a, 48b, 48c must be secured and can optionally be equipped with buoyancy elements 52, so that they always slope downv/ards towards the points of discharge 45a, 45b 45c in order to avoid liquid build ⁇ up of heavier hydrocarbons in the hoses 48a, 48b, 48c.
• Fig. 4b shows in principle the same concept as fig.
• Fig. 4c shows a construction, where the points of discharge is situated on a corresponding type of underwater buoy 53 which in a similar manner is secured by way of a flexible joint 54 to the sea-bed 11.
• the actual underwater main pipe or line consists however, of three separate pipes 55 which extend downwards along ⁇ side the shaft of the platform to the sea-bed 41 and via flexible hoses on the sea-bed 41 and via flexible hoses on the sea-bed 41 and upwards alongside the underwater buoy 53 to their respective points of discharge.
• the most important advantage of such a con ⁇ cept will be that, as opposed to the solutions in fig. 4a-b, there are no hoses or pipes floating freely at various depths between the platform and the underwater anchoring arrangement.
• a disadvantage with the concept will be the danger of liquid build-up of heavier hydrocarbons in the flexible pipes which extend along the sea bed.
• Fig. 4d shows a conceptual design where rigid pipes 58a, 58b, 58c extend from the line 13 alongside the platform shaft 47 out to the respective points of discharge.
• the pipes are supported by frame-work structures 57a, 57b, 57c which in the shown embodiment are in the shape of triangular towers.
• Each corner can for instance consist of pipes where one of the pipes can be a gas discharge pipe.
• the lower point of discharge 59a can be mounted onto a smaller framework tower on the sea bed 11.
• the framework structures are spread around the platform 40 in order to spread the loads.
• An advantageous characteristic of this embodiment is that the system is independent of movements between the platform 40 and the sea bed 41.
• FIG. 4e shows a corresponding embodiment with rigid pipes 58a, 58b, 58c, as in fig. 4d, but where the points of discharge are supported by a framework tower 60 which rests on the sea bed 11, and where framework bridges 61 are stretched between the tower 60 and the platform 40 to support the pipes.
• a method for depressurization of process equipment on platforms off-shore according to the invention can comprise the following steps:
• - high-pressure gas is relieved through an underwater gas-release system to a predetermined level, after which further relieval takes place through a choke or a valve which opens in a side ⁇ line for pressure-relief in a conventional system.

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• Engineering & Computer Science (AREA)
• Mining & Mineral Resources (AREA)
• Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Environmental & Geological Engineering (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Processing Of Solid Wastes (AREA)
• Excavating Of Shafts Or Tunnels (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Earth Drilling (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=19889742

Family Applications (1)

Country Status (5)

Cited By (1)

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Citations (4)

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• 1987
  • 1987-03-05 NO NO870910A patent/NO870910L/no unknown
• 1988
  • 1988-03-01 WO PCT/NO1988/000016 patent/WO1988006674A1/en unknown
  • 1988-03-01 BR BR888805854A patent/BR8805854A/pt unknown
  • 1988-03-04 FR FR8802792A patent/FR2612247A1/fr not_active Withdrawn
  • 1988-11-01 GB GB8825478A patent/GB2209781A/en not_active Withdrawn

Patent Citations (4)

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