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
  • E21B19/00—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables
  • E21B19/002—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling
  • E21B19/004—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling supporting a riser from a drilling or production platform
  • E21B19/006—Handling rods, casings, tubes or the like outside the borehole, e.g. in the derrick; Apparatus for feeding the rods or cables specially adapted for underwater drilling supporting a riser from a drilling or production platform including heave compensators
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S285/00—Pipe joints or couplings
  • Y10S285/90—Balanced pressure

Definitions

• the present invention relates to a method for compensa ⁇ ting the movements of a riser pipe running between a mobile offshore structure and a wellhead on the sea-bed, in which the riser pipe is connected fixedly to the offshore struc ⁇ ture and at its upper end equipped with a sliding joint and a movement-compensated suspension assembly comprising at least one hydraulic cylinder for that section of the riser pipe which is below the sliding joint.
• Such compensation for movement is common when oil and gas wells are being drilled from a mobile rig, for instance a semi-submersible rig or a drilling vessel.
• the sliding joint will here compensate for the varying distance between the well-head and the drilling rig which is caused by tides, the heaving movements of the rig because of waves, and the drift of the rig.
• the pressure inside the riser pipe is comparative ⁇ ly low.
• the pressure may increase if a shallow pocket of gas is encountered, and the sliding joint is therefore generally designed to withstand a pressure in the order of magnitude of 35 bar during a shorter period of time.
• Production riser pipes for mobile production platforms where there has been a requirement for vertical accessability in the well, have therefore been constructed as an integrated unit suspended in tension systems and guides, capable of absorbing the necessary strokes and angular deviations.
• Such rigid riser pipes present the drawback that all operations must be based on moving systems (production trees, blow-out preventer valves etc.) with correspondingly complicated connections. Furthermore, a complicated, voluminous and expensive tension suspension system is required.
• the aim of the present invention is to provide a method 5 for compensating the movements of riser pipes which is not encumbered by the above mentioned shortcomings and draw ⁇ backs.
• volume bal ⁇ anced shall be deemed to mean that the telescoping device may be extended and compressed without any net conveyance of fluid taking place into or out of it.
• Pressure balanced 15 shall be deemed to mean that there will be no effect of axial forces seeking to urge the parts of the telescoping device apart, regardless of the internal pressure.
• the pressure balancing causes the sliding joint to be 20 capable of tolerating very high internal pressures without axial forces being created which will need to be absorbed by the usual tension suspension system. Consequently, it will only be necessary to dimension for the tension which must be maintained in the riser pipe below the sliding joint, with 25. ensuing major savings.
• the volume balancing permits axial movements in the sliding joint even if the riser pipe should happen to be shut at both ends in an emergency.
• the platform will thus be able to make maximal heaving movements in such a situa- 30 tion without experiencing fluctuations of pressure nor any other resistance to the telescoping of the sliding joint.
• the sliding joint used is a telescoping device which com ⁇ prises a telescope casing with an internal cylinder surface, a telescopic pipe which has an external cylinder surface and is sealedly and slidingly arranged in the telescope casing, an annular piston on the outside of the telescopic pipe in contact with the internal cylinder surface of the telescope casing, so that a chamber is formed on either side of the piston, one of which communicates with the inside of the te ⁇ lescope casing, and the other one communicates with a source of fluid of substantially constant pressure, the cross sec- tion area of the internal cylinder surface of the telescope casing being twice that of the cross section area of the ex ⁇ ternal cylinder surface of the telescopic pipe.
• a similar telescopic device is more or less known from US Patent No. 2 373 280, issued on 10 April 1945.
• This pre- viously known device was developed as a pressure balanced thermal expansion joint for pipes in plants for the manufac ⁇ ture of synthetic rubber where temperatures could become very high.
• the patent is silent on volume balancing, and it is possible that the inventor has not been aware of this characteristic of the expansion joint, since it was not re ⁇ quired for his purpose. In any circumstances, nobody ap ⁇ pears to have realized previously that a similar telescoping joint could advantageously be used in riser pipes for the production of oil and gas from mobile platforms.
• the hydraulic cylinder of the suspension assembly be incorporated into the telescoping device.
• This may for instance be done by arranging the hydraulic cylinder as an annular casing round a cylindrical surface on the out ⁇ side of the telescoping device, which is provided with an annular collar to form the piston of the hydraulic cylinder, the annular casing being connected, directly or indirectly, to the offshore installation.
• the usual tension cables are obviated, with their comparatively complicated tension cylinders and an un ⁇ complicated, compact, robust and dependable unit is obtained which handles both the movement compensation and the tension function.
• connection between the said one chamber and the inside of the telescopic pipe by way of a pressure vessel with a movable partition, preferably a cylinder with a floating piston.
• the invention also relates to a telescoping device as defined in patent claims 6 to 10.
• Fig. 1 shows a schematic outline, partly in section, of an offshore well installation and a riser pipe which is equipped with a device according to the invention and which leads from the well installation t.o the mobile platform above.
• Fig. 2 shows an axial section through a telescopic device according to the invention. ' -.
• Fig. 3 shows an axial section through a modification of the telescopic device of fig. 2.
• Fig. 4 shows a lengthwise section of a modification of the embodiment of fig. 3.
• Fig. 5 shows a lengthwise section of one variety of the
• the well ⁇ head comprises a valve tree 2, a pipe suspension assembly 3 and bushing pipes 4 of various diameters extending into the ground. This also applies to a production pipe 5.
• riser pise 6 extends upwards to a mobile rig structure, only indicated with its production deck 7 and BOP-deck 8.
• the riser pipe 6 is connected to a telescopic device 9 according to the invention which is attached underneath the production deck 7 of the platform. From the telescopic device the riser pipe continues upwards to a BOP 10, and between this and the telescopic device, a production pipe 11 branches off.
• the construction of the telescopic device 9 is further illustrated in fig. 2.
• the telescopic device comprises a telescope casing 13, which has an internal sylinder surface 14 of diameter D.
• a sealing area 16 provides a seal between the telescopic pipe 15 and the upper end of the telescope casing 13, while a second sealing area 17 provides a seal against the telescopic pipe at an internal collar 18 inside the telescope casing.
• the telescopic pipe 15 is provided with an annular piston 19 which, by means of a sealing area 20, provides a seal against the internal cylinder surface 14 of the telescope casing 13.
• annular chamber 21 is created above the piston 19, and a lower annular chamber 22 under ⁇ neath the piston.
• the cross section area of these chambers 21, 22 and the piston 19 is, because of the ratio stated above of diameter D to diameter d, equal to the external cross section area of the telescopic pipe 15.
• the upper chamber 21 communicates with the inside of the telescopic pipe 15 through ports 23 in the telescopic pipe.
• the lower chamber 22 communicates with the ambient atmosphere via ports 24 in the telescope casing 13.
• the same pressure will prevail in the chamber 21 as in the telescopic pipe 15 and the lower part of the telescope casing 13.
• the area of the piston 19 equals the cross section area of the telescopis pipe 15, the force with which the pressure in the lower part 25 of the telescope casing seeks to expel the telescopic pipe 15, will be pre ⁇ cisely balanced by the force acting in the opposite direc ⁇ tion against the piston 19.
• the gliding joint formed by the telescope casing 13 and the telescopic pipe 15, is thus com ⁇ pletely pressure balanced.
• the telescopic pipe 15 If one envisages that the telescopic pipe 15 is being pushed into the telescope casing 13, the telescopic pipe will displace fluid from the lower part 25 of the telescope casing. However, the volume of the upper chamber 21 will increase to exactly the same degree so that any fluid dis ⁇ placed from the lower chamber 25 will flow through the ports 23 and into the upper chamber 21. There is consequently no net conveyance of fluid into or out of the telescopic device 9 from relative movements between the telescopic pipe and the telescope casing, and the sliding joint formed by them is thus completely volume balanced.
• a very straightforward way has been found in which to solve the problem of tension. This is done by using a hydraulic cylinder in connection with the telescopic device itself, to exert the required lifting force in the telescope casing.
• the telescope casing 13 is here provided with a piston in the form of an outside flange 26 which provides a gliding seal against a cylinder 27 arranged round the telescope casing.
• the cylinder 27 is sealed against the telescope casing at 28 below the piston 26, to provide a cylinder chamber 29.
• This chamber communicates through a conduit 30 with a source of hydrualic fluid at constant pressure, e.g. the usual battery of accumulators.
• the cylinder 27 is at its upper end provided with a flange 31 and this in turn is by means of bolts 32 fixedly attached to a flange 33 on the upper part of the riser pipe 6.
• This in turn is fixedly connected to the production deck of the platform 7, so that the tensile forces are transfer- red to the deck.
• the well fluid produced contains abrasive impurities which it is desirable to keep away from the seals of the te ⁇ lescopic device, particularly in the annular chamber 21 shown in fig. 2, it is possible to proceed as indicated in fig. 3. There are here no ports 23 between the inside of the telescopic pipe 15 and the chamber 21.
• the sealing area 17 is somewhat less exposed, be ⁇ cause impurities in the well fluid are unable to form a sediment on its upper surface, but in order to give it extra protection, it may be provided with injection of pure oil, for instance taken from the chamber 29 of the tension cylin ⁇ ders through a duct in the piston 26, the body of the tele ⁇ scope casing and the internal collar 18.
• this connection may be placed openly between the piston 26 and the collar 18 so that a non-return valve may be positioned here to prevent inadvertent return flow of well fluid to the chamber 29.
• Fig. 4 shows a modification of the hydraulic cylinder for maintaining tension in the riser pipe.
• the press ⁇ ure vessel 34 has been extended by means of an auxiliary cylinder 38 in which is arranged an auxiliary piston 39.
• the auxiliary piston 39 is connected to the piston 35 of the pressure vessel via a piston rod 40 which is carried sealed- ly through a fixed partition wall 41 between the pressure vessel 34 and the auxiliary cylinder 38.
• the conduit 30 from the battery of accumulators communicates with the auxiliary cylinder below the piston 39.
• a piston 42 is con ⁇ nected to the underside of the piston 35 and carried through the bottom of the pressure vessel 34 in order to provide the same effective area on both sides of the piston 35.
• the piston rod 42 may be obviated for instance by executing the piston 35 as a differential piston.
• the tension in the riser pipe is produced by, in the annular chamber 21 , in addition to the internal pressure
• This superimposed pressure is created in the chamber 37 of the pressure vessel 34 by supplying an appropriate pressure to the auxiliary cylinder 38 through the conduit 30.
• Fig. 5 illustrates a further example of how the tension cylinder may be combined with the telescopic device.
• Used here as the basis is the embodiment of the telescope casing and the telescopic pipe shown in fig. 2.
• the external cylinder 27 has been removed and has instead been replaced by a cylinder 43 which constitutes an extension of the tele- scope casing 13.
• the telescopic pipe 15 is provided with a corresponding extension 44, having an annular piston 45 slidingly arranged in the cylinder 43.
• the cylinder chamber above the piston 45 communicates with the battery of accumu ⁇ lators or the like through the conduit 30.
• This embodiment lends greater length to the telescopic device, something which may be a restricting factor if the telescopic device needs to be able to cater for strokes of 7.5 m or more, but provides the advantage in comparison with the embodiment of fig. 4 that the differential pressure above the sealing area 16 will be lower.
• the telescopic device may be turned upside-down so that the telescope casing is fitted fixedly to the platform while the telescopic pipe is connected to the lower part of the riser pipe.
• the pressure vessel 34 of fig. 3 may be given a number of different embodiments, the piston 35 may for example be replaced by a sufficiently flexible membrane, and it will here be possible to use an ordinary hydraulic accumulator as the pressure vessel.
• the telesco ⁇ pic device may advantageously be provided with e.g. hydraul- ically operated attachments at both ends to afford brief in ⁇ stallation and dismantlig time for maintenance and possible - replacement.
• the upper part of the lower section of the riser pipe may be provided with a sus ⁇ pension device.

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• Engineering & Computer Science (AREA)
• Geology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Physics & Mathematics (AREA)
• Environmental & Geological Engineering (AREA)
• Fluid Mechanics (AREA)
• Mechanical Engineering (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Earth Drilling (AREA)
• Rod-Shaped Construction Members (AREA)
• Load-Engaging Elements For Cranes (AREA)

Priority Applications (4)

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Publications (1)

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Cited By (14)

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Citations (3)

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• 1988
  • 1988-11-09 NO NO885006A patent/NO169027C/no unknown
• 1989
  • 1989-11-08 WO PCT/NO1989/000116 patent/WO1990005236A1/en active IP Right Grant
  • 1989-11-08 DE DE68918937T patent/DE68918937T2/de not_active Expired - Fee Related
  • 1989-11-08 US US07/536,668 patent/US5069488A/en not_active Expired - Fee Related
  • 1989-11-08 EP EP89912504A patent/EP0408685B1/en not_active Expired - Lifetime
  • 1989-11-08 BR BR898907159A patent/BR8907159A/pt not_active IP Right Cessation
• 1990
  • 1990-07-03 DK DK159790A patent/DK159790A/da not_active Application Discontinuation

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