WO2018070879A1 - Tubular steel lattice drilling tower structure - Google Patents

Tubular steel lattice drilling tower structure Download PDF

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Publication number
WO2018070879A1
WO2018070879A1 PCT/NO2017/050265 NO2017050265W WO2018070879A1 WO 2018070879 A1 WO2018070879 A1 WO 2018070879A1 NO 2017050265 W NO2017050265 W NO 2017050265W WO 2018070879 A1 WO2018070879 A1 WO 2018070879A1
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WO
WIPO (PCT)
Prior art keywords
jacket
cps
tower structure
braces
offshore
Prior art date
Application number
PCT/NO2017/050265
Other languages
French (fr)
Inventor
Rene Pascal Emile Freund
Original Assignee
Borealis Offshore Consultants As
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Borealis Offshore Consultants As filed Critical Borealis Offshore Consultants As
Publication of WO2018070879A1 publication Critical patent/WO2018070879A1/en

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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
    • 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
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B17/02—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto
    • E02B17/027—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor placed by lowering the supporting construction to the bottom, e.g. with subsequent fixing thereto steel structures
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B17/00—Artificial islands mounted on piles or like supports, e.g. platforms on raisable legs or offshore constructions; Construction methods therefor
    • E02B2017/0056—Platforms with supporting legs
    • E02B2017/006—Platforms with supporting legs with lattice style supporting legs
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2240/00—Components
    • F05B2240/90—Mounting on supporting structures or systems
    • F05B2240/95—Mounting on supporting structures or systems offshore
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
    • F05B2240/00—Components
    • F05B2240/90—Mounting on supporting structures or systems
    • F05B2240/97—Mounting on supporting structures or systems on a submerged structure

Definitions

  • SLIMTWIS presents a tubular steel lattice tower structure formed by two parts twisted 45 deg. with respect to each other which is aimed at supporting a minimal offshore topside and guiding vertical conductor pipes in medium water depths typical of the North Sea.
  • This invention extends the concept of the twisted base previously implemented on the UKCS in water depths of about 90 m (Elgin-Franklin, Shearwater, ETAP, Culzean) to deeper water up to 150 m which correspond to the present limits of the most advanced jack-up (JU) drilling units.
  • UWPs Ultra-manned wellhead platforms
  • Norwegian authorities have recently been promoted by the Norwegian authorities as an alternative to subsea templates for tapping reserves at the periphery of a main reservoir initially produced via the heavy facilities of a central complex.
  • UWP jacket may remain slightly more expensive to fabricate and install than a subsea structure in terms of capital expenditure
  • a battered jacket is a most effective solution for carrying loads in offshore drilling platforms and actually about 95% of the fixed offshore platforms in the world, irrespective of the water depths, are using this carrying structure.
  • One of the problems that arises with depth is to obtain a structure that is able to withstand the bending forces exerted on the carrying structure from natural forces such as currents, tides, waves, wind, etc. and current structures are normally not able to cope with extreme conditions existing e.g. in the North Sea.
  • One of the considerations to take into account is to lead the forces exerted on the lattice structure along the axial centre line of the pipes or girders included in the structure and to avoid configurations that will remove the attack points of such forces from such axial centre lines.
  • the location of the joints between the twisted section and its immediate vertically adjacent section(s) is an example of the considerations to take when designing a twisted lattice structure. This is illustrated by the prior art structures referred to supra.
  • the purpose of this invention is therefore to widen the application range of these UWP structures, allowing them to match the capacities of the most recent harsh environment jack-up units.
  • a UWP must be economical by comparison to a subsea template alternative. Therefore material, fabrication and installation costs of this jacket are kept to a minimum.
  • its upper part is standardized for all installations on the same field, whereas only its lower part is slightly adapted to the particulars (bathymetry, soil conditions) of its specific location on the field.
  • a UWP is by essence a lightweight structure by comparison to a more conventional offshore jacket where heavy gravity loads ensure that the foundation experiences essentially one-way compressive cycles during storms. Conversely the environmental loads which prevail on a UWP cause large overturning moments and generate two-way tension-compression cycles causing a friction fatigue
  • the UWP must provide adequate protection to the wells against accidental high energy collision by a drifting supply vessel. To that respect sufficient clearance must be maintained between the peripheral belt of the jacket and the conductor pipes (CPs) which are therefore grouped in a compact array at the centre of the jacket.
  • CPs conductor pipes
  • the respective foundations of the UWP jacket and of the JU must remain sufficiently remote from each other in order to avoid interfering. This is achieved by rotating the lower part of the jacket by 45 deg . in order that the foundation facing the JU at one corner of the jacket (pile cluster or suction bucket) is located midway between two spud cans.
  • the lattice jacket structure according to the present invention consists essentially of two tubular lattice towers, the upper one being twisted 45 deg. with respect to the lower one.
  • Fig. 1 displays an embodiment of a lattice structure according to the invention to be included in a twisted tower structure.
  • Fig. 2 displays an embodiment of a bottom section for carrying a lattice structure.
  • Fig. 3 displays an embodiment of assembled bottom and above twisted lattice structure.
  • Fig. 4 displays an embodiment of a joint between respective lattice structures being twisted with respect to each other.
  • Fig. 5 displays an embodiment of a wellhead lattice structure.
  • Fig. 6 displays a bird's eye view of the lattice structure shown in Fig. 5.
  • the upper part of the jacket is of constant square section approximately 14.0 m x 14.0 m with vertical legs located in the NW, NE, SW and SE corners of the square running down to the interface level located approximately 40% down of the water depth.
  • the four vertical faces are braced by X-diagonals, which should provide adequate protection for boat impact across the splash zone, whereas horizontal elevations guiding the CPs are diamond shaped.
  • the lower part consists of a traditional jacket characterized by a square plane cross-section with sizes increasing linearly with depth. This part is twisted 45 deg. with respect to the upper part and the battered legs are located in the N, W, E and S corners of the square.
  • the four battered faces and the horizontal elevations guiding the CPs are braced by X-diagonals, except at top interface where diamond- shaped diagonals are used to provide continuity with the pattern on the upper part.
  • the top of this jacket constitutes the transition where two large diameter bracings which initiate at the base of one leg of the upper part frame into the top of the two adjacent legs of the lower part, respectively. These bracings are contained in the plan of the battered face of the lower jacket.
  • the foundation at each corner of the square footprint may consist of either
  • the foundation is principally designed to resist the two- way tensile-compressive cycles generated by severe storms which cause severe downgrading of the soil characteristics.
  • the upper part consists of a 14.0 m x 14.0 m square and accommodates 10 x 3O"0 CPs in a 4 + 4 + 2 arrangement.
  • the CPs are guided by diamond-shaped bracings at the top, mid-height and bottom of this upper part, resulting in freespans of approximately 26.0 m.
  • a larger variant of this structure would consist of a 21.0 m x 21.0 m square accommodating 16 x 3O"0 CPs in a 6 + 6 + 2 + 2 arrangement.
  • the CPs are guided at the main elevations of the lower part of the jacket by horizontal X-bracings running between the corner legs resulting to freespans between 28.0 and 36.0 m.
  • the jacket can additionally accommodate one or two caissons and/or J-tubes plus several small diameter risers. Rather than running the risers along the legs at tight spacing to prevent their vortex-shedding vibration, these are clustered around the J-tube(s) forming a riser ladder with the vertical J-tube as spine. Typical Dimensions
  • the upper and lower parts can be assembled together on the yard and the entire jacket loaded out horizontally by trailers on the transportation barge.
  • a heavy sea- fastening will be required in order to secure the two pile clusters (or buckets) highest up in the air, as well as cradles to support the upper part rotated by 45 deg.
  • An alternative to this single-piece load-out and transportation would consist of loading and shipping the two parts separately
  • the present invention may be indicated by a structure comprising a tubular steel lattice tower structure formed by two parts twisted 45 deg. with respect to each other, which is aimed at supporting a minimal offshore topside and guiding vertical conductor pipes in medium water depths up to about 150 m.
  • the upper jacket part of the structure according to the invention has in one embodiment a constant square cross-section with vertical legs supporting the CPs by diamond-shape braces.
  • the lower jacket part of the structure according to the invention includes in one embodiment a square cross-section with sizes increasing linearly with depth and battered legs supporting the CPs by X-braces.
  • the structure according to the invention includes a transition between the two parts located approximately 40% down of the water depth, which is constituted by pairs of large diameter braces connecting the base of each leg on the upper part to the top of the two adjacent legs on the lower part.

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  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Geology (AREA)
  • Mining & Mineral Resources (AREA)
  • Mechanical Engineering (AREA)
  • Fluid Mechanics (AREA)
  • Geochemistry & Mineralogy (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Bulkheads Adapted To Foundation Construction (AREA)
  • Earth Drilling (AREA)
  • Foundations (AREA)

Abstract

A steel lattice tower structure for supporting minimum offshore facilities, which is formed by two parts twisted 45 deg. with respect to each other, the upper and lower parts having respectively vertical and battered legs, connected to each other by a transition truss located approximately 40% down of the water depth. The present invention also includes a procedure for fabricating and installing the entire structure as two separate units assembled offshore.

Description

TUBULAR STEEL LATTICE DRILLING TOWER STRUCTURE
Ambit of the Invention
The present invention, referred to hereafter as SLIMTWIS, presents a tubular steel lattice tower structure formed by two parts twisted 45 deg. with respect to each other which is aimed at supporting a minimal offshore topside and guiding vertical conductor pipes in medium water depths typical of the North Sea.
General Disclosure of the Invention
This invention extends the concept of the twisted base previously implemented on the UKCS in water depths of about 90 m (Elgin-Franklin, Shearwater, ETAP, Culzean) to deeper water up to 150 m which correspond to the present limits of the most advanced jack-up (JU) drilling units.
Minimal unmanned wellhead platforms (UWPs) have recently been promoted by the Norwegian authorities as an alternative to subsea templates for tapping reserves at the periphery of a main reservoir initially produced via the heavy facilities of a central complex. Whereas a UWP jacket may remain slightly more expensive to fabricate and install than a subsea structure in terms of capital expenditure
(CAPEX), it is expected to be cheaper to operate and maintain (OPEX) throughout its lifetime. A UWP facility where all equipment is located above sea surface also provides a higher degree of reliability and safety compared to a subsea template. Prior Art
The twisting of lattice structures in offshore drilling towers has previously been suggested in UK patent applications GB 2 282 839 A and GB 2 366 820 A.
However, a mere twisting of sections in a tower structure is not sufficient to provide a substantially improved tower structure. Several considerations have to be taken into account when twisting a lattice structure in order not to weaken the overall performance of such a structure.
Practice has shown that a battered jacket is a most effective solution for carrying loads in offshore drilling platforms and actually about 95% of the fixed offshore platforms in the world, irrespective of the water depths, are using this carrying structure. One of the problems that arises with depth is to obtain a structure that is able to withstand the bending forces exerted on the carrying structure from natural forces such as currents, tides, waves, wind, etc. and current structures are normally not able to cope with extreme conditions existing e.g. in the North Sea. One of the considerations to take into account is to lead the forces exerted on the lattice structure along the axial centre line of the pipes or girders included in the structure and to avoid configurations that will remove the attack points of such forces from such axial centre lines. The location of the joints between the twisted section and its immediate vertically adjacent section(s) is an example of the considerations to take when designing a twisted lattice structure. This is illustrated by the prior art structures referred to supra.
The purpose of this invention is therefore to widen the application range of these UWP structures, allowing them to match the capacities of the most recent harsh environment jack-up units.
Despite, but also because of, its simplicity a minimal UWP platform needs to face the following challenges
1. A UWP must be economical by comparison to a subsea template alternative. Therefore material, fabrication and installation costs of this jacket are kept to a minimum. In particular, its upper part is standardized for all installations on the same field, whereas only its lower part is slightly adapted to the particulars (bathymetry, soil conditions) of its specific location on the field.
2. A UWP is by essence a lightweight structure by comparison to a more conventional offshore jacket where heavy gravity loads ensure that the foundation experiences essentially one-way compressive cycles during storms. Conversely the environmental loads which prevail on a UWP cause large overturning moments and generate two-way tension-compression cycles causing a friction fatigue
phenomenon which may considerably downgrade the capacity of the soil surrounding the foundation. To that respect it is essential to make the jacket as transparent to the wave as feasible, especially across the splash zone where water particle kinematics combined with the lever arm with respect to the sea bottom are highest.
3. The UWP must provide adequate protection to the wells against accidental high energy collision by a drifting supply vessel. To that respect sufficient clearance must be maintained between the peripheral belt of the jacket and the conductor pipes (CPs) which are therefore grouped in a compact array at the centre of the jacket.
4. Conversely the slots must remain sufficiently close to the work-over jack-up in order to minimize the outreach of the cantilevered rig. This is achieved by designing the upper part of the UWP jacket with vertical faces, one of them parallel to the hull of the JU.
5. The respective foundations of the UWP jacket and of the JU (spud cans) must remain sufficiently remote from each other in order to avoid interfering. This is achieved by rotating the lower part of the jacket by 45 deg . in order that the foundation facing the JU at one corner of the jacket (pile cluster or suction bucket) is located midway between two spud cans.
6. Keep equipment layout simple. Here the main rows of the topside are aligned with the rows of the upper part of the jacket, also creating wide open bays facing the JU. STRUCTURE DESCRIPTION
The lattice jacket structure according to the present invention consists essentially of two tubular lattice towers, the upper one being twisted 45 deg. with respect to the lower one.
This structure of the sections is illustrated in the enclosed figures wherein Fig. 1 displays an embodiment of a lattice structure according to the invention to be included in a twisted tower structure.
Fig. 2 displays an embodiment of a bottom section for carrying a lattice structure.
Fig. 3 displays an embodiment of assembled bottom and above twisted lattice structure. Fig. 4 displays an embodiment of a joint between respective lattice structures being twisted with respect to each other.
Fig. 5 displays an embodiment of a wellhead lattice structure. Fig. 6 displays a bird's eye view of the lattice structure shown in Fig. 5. Upper Part
The upper part of the jacket is of constant square section approximately 14.0 m x 14.0 m with vertical legs located in the NW, NE, SW and SE corners of the square running down to the interface level located approximately 40% down of the water depth. The four vertical faces are braced by X-diagonals, which should provide adequate protection for boat impact across the splash zone, whereas horizontal elevations guiding the CPs are diamond shaped.
It is anticipated that this upper structure remains identical for all UWPs to be installed on the same field as long as the properties of the hydrocarbon reservoir are uniform and therefore require identical equipment at topside including risers and umbilicals.
Lower Part
The lower part consists of a traditional jacket characterized by a square plane cross-section with sizes increasing linearly with depth. This part is twisted 45 deg. with respect to the upper part and the battered legs are located in the N, W, E and S corners of the square. The four battered faces and the horizontal elevations guiding the CPs are braced by X-diagonals, except at top interface where diamond- shaped diagonals are used to provide continuity with the pattern on the upper part. The top of this jacket constitutes the transition where two large diameter bracings which initiate at the base of one leg of the upper part frame into the top of the two adjacent legs of the lower part, respectively. These bracings are contained in the plan of the battered face of the lower jacket.
An identical batter of about 1/8 is optimally enforced for all structures aimed at the same field, with only the width of the square footprint requiring adaptation to suit the bathymetry at the exact location. At most North Sea locations, the variations of water depth over a same field seldom exceed ±5.0 m, therefore lower bases should also be virtually identical to each other. Foundations
The foundation at each corner of the square footprint may consist of either
- a traditional cluster of 2 to 4 piles, depending on soil characteristics and water depth. Each pile is driven to target penetration by an underwater hammer then grouted to the jacket sleeve,
- a suction caisson driven into the sea bottom by pressure differential.
Under both configurations the foundation is principally designed to resist the two- way tensile-compressive cycles generated by severe storms which cause severe downgrading of the soil characteristics.
Apputrenances
In a standard configuration, the upper part consists of a 14.0 m x 14.0 m square and accommodates 10 x 3O"0 CPs in a 4 + 4 + 2 arrangement. The CPs are guided by diamond-shaped bracings at the top, mid-height and bottom of this upper part, resulting in freespans of approximately 26.0 m.
A larger variant of this structure would consist of a 21.0 m x 21.0 m square accommodating 16 x 3O"0 CPs in a 6 + 6 + 2 + 2 arrangement.
The CPs are guided at the main elevations of the lower part of the jacket by horizontal X-bracings running between the corner legs resulting to freespans between 28.0 and 36.0 m.
The jacket can additionally accommodate one or two caissons and/or J-tubes plus several small diameter risers. Rather than running the risers along the legs at tight spacing to prevent their vortex-shedding vibration, these are clustered around the J-tube(s) forming a riser ladder with the vertical J-tube as spine. Typical Dimensions
The figures below are representative of a SLIMTWIS structure accommodating 10 slots in 112 m water depth typical of Central North Sea. Whereas these figures are believed to be realistic, they are only indicative and would need to be adapted to suit the particulars of a given location in terms of bathymetry, environmental and geotechnical conditions and reservoir characteristics.
- Square upper part 14.0 m x 14.0 m,
- Interface between the two parts El. -42.0 m,
- Square footprint at seabed 32.0 m x 32.0 m,
- Lower legs batter « 1/8
- CP array 4 + 4 + 2 @ 2.50 m spacing
- CP guides El. + 11.50 m, -15.25 m, -42.0 m, -73.0 m and -106.0 m,
- 100-year extreme wave height 28.0 m
- Soil conditions dense sand and very stiff clay layers
- Foundation four clusters of 3 x 96"OD piles driven 50 m below seabed,
- Operating weight topside 1000 mT,
- Not to Exceed (NTE) jacket weight 4200 mT
- J-Tube 1 x 28"0
- Risers 1 x 12"0 multiphase export + 1 x 1O"0 gas injection import
- Caisson 1 x 24"0 open drain FABRICATION & INSTALLATION Fabrication
It is anticipated that the upper and lower parts of the jacket will be fabricated separately, possibly on two different construction yards.
Standardization of the upper part in particular permits that specific details are produced in series. In particular some critical nodes like those in the transition zone may be cast instead of welded, which would considerably enhance their endurance to fatigue. Load-Out and Transportation
The upper and lower parts can be assembled together on the yard and the entire jacket loaded out horizontally by trailers on the transportation barge. A heavy sea- fastening will be required in order to secure the two pile clusters (or buckets) highest up in the air, as well as cradles to support the upper part rotated by 45 deg. An alternative to this single-piece load-out and transportation would consist of loading and shipping the two parts separately
- the upper part horizontally and flat, which requires minimum sea-fastening because of its comparatively small and constant cross-section,
- the lower part vertically, a procedure previously implemented for the "Gyda" jacket which demands less sea-fastening and also eliminates potential additional permanent bracing on the structure.
Lifting and Upending
It is expected that the entire jacket can be lifted and upended in one piece by the twin cranes of a semi-submersible crane vessel (SSCV) even in its tallest configuration. On-bottom stability may however prove to be critical here due to the comparatively light weight of this structure, therefore tight weather windows must be imposed for the entire operation to proceed safely.
Conversely these on-bottom stability restrictions do not hamper the installation of the lower part as a separate unit, which could even be lowered vertically by the single crane of a monohull crane vessel before piles are driven and grouted, probably without the need of grippers. The upper part is then stabbed on top of it either immediately afterwards, or during a second campaign if the lower part is first used as underwater template for pre-drilling the wells. On-site connection between the upper and lower parts of the jacket can be achieved either by grouting (as successfully implemented earlier on the Kvitebjorn jacket where the interface was much deeper at El. -145.0 m) or by mechanical swaging.
In summary, the present invention may be indicated by a structure comprising a tubular steel lattice tower structure formed by two parts twisted 45 deg. with respect to each other, which is aimed at supporting a minimal offshore topside and guiding vertical conductor pipes in medium water depths up to about 150 m.
The upper jacket part of the structure according to the invention has in one embodiment a constant square cross-section with vertical legs supporting the CPs by diamond-shape braces. The lower jacket part of the structure according to the invention includes in one embodiment a square cross-section with sizes increasing linearly with depth and battered legs supporting the CPs by X-braces.
The structure according to the invention includes a transition between the two parts located approximately 40% down of the water depth, which is constituted by pairs of large diameter braces connecting the base of each leg on the upper part to the top of the two adjacent legs on the lower part.
For producing and erecting a structure as disclosed supra, there may be used a procedure to fabricate and install the entire jacket, either as a single unit assembled onshore, or as two separate parts connected at the offshore site.

Claims

C l a i m s
1. Tubular steel lattice tower structure formed by two parts twisted 45 deg . with respect to each other, which is aimed at supporting a minimal offshore topside and guiding vertical conductor pipes in medium water depths up to about 150 m.
2. Upper jacket part of constant square cross-section with vertical legs supporting the CPs by diamond-shape braces.
3. Lower jacket part of square cross-section with sizes increasing linearly with depth and battered legs supporting the CPs by X-braces.
4. Transition between the two parts located approximately 40% down of the water depth, which is constituted by pairs of large diameter braces connecting the base of each leg on the upper part to the top of the two adjacent legs on the lower part.
5. Procedure to fabricate and install the entire jacket, either as a single unit assembled onshore, or as two separate parts connected at the offshore site.
PCT/NO2017/050265 2016-10-14 2017-10-13 Tubular steel lattice drilling tower structure WO2018070879A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO20161645 2016-10-14
NO20161645A NO20161645A1 (en) 2016-10-14 2016-10-14 Slim twisted jacket for unmanned wellhead platforms

Publications (1)

Publication Number Publication Date
WO2018070879A1 true WO2018070879A1 (en) 2018-04-19

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2323086A1 (en) * 1975-09-08 1977-04-01 Hydrotech Int Inc Pipe union for tubular frame oil rig - has flange on one pipe with sloping front and rear faces
GB2282839A (en) 1993-10-13 1995-04-19 Kvaerner Earl & Wright Offshore tower structure
GB2366820A (en) 2000-09-15 2002-03-20 Kvaerner Oil & Gas Ltd Offshore tower structure

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2323086A1 (en) * 1975-09-08 1977-04-01 Hydrotech Int Inc Pipe union for tubular frame oil rig - has flange on one pipe with sloping front and rear faces
GB2282839A (en) 1993-10-13 1995-04-19 Kvaerner Earl & Wright Offshore tower structure
GB2366820A (en) 2000-09-15 2002-03-20 Kvaerner Oil & Gas Ltd Offshore tower structure

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
KNUT ENGENE: "Subsea On a Stick", KVAERNER, 31 March 2016 (2016-03-31), XP055444035, Retrieved from the Internet <URL:http://www.norskehavskonferansen.no/file=3144> [retrieved on 20180124] *

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