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EP 0 910 708 B1 |
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EUROPEAN PATENT SPECIFICATION |
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Mention of the grant of the patent: |
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09.04.2003 Bulletin 2003/15 |
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Date of filing: 12.06.1997 |
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International Patent Classification (IPC)7: E02B 17/02 |
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International application number: |
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PCT/EP9703/110 |
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International publication number: |
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WO 9704/8858 (24.12.1997 Gazette 1997/55) |
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LIGHTWEIGHT OFFSHORE PLATFORM STRUCTURE
LEICHTGEWICHT STRUKTUR FÜR EINE OFFSHORE-PLATTFORM
STRUCTURE PLATE-FORME DE FORAGE LEGERE
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Designated Contracting States: |
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DK GB NL |
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Priority: |
17.06.1996 EP 96201687
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Date of publication of application: |
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28.04.1999 Bulletin 1999/17 |
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Proprietor: SHELL INTERNATIONALE RESEARCH
MAATSCHAPPIJ B.V. |
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2596 HR Den Haag (NL) |
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Inventor: |
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- VAN DE GRAAF, Jan, Willem
NL-2596 The Hague (NL)
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References cited: :
GB-A- 2 000 211 US-A- 4 326 595
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GB-A- 2 065 198 US-A- 5 051 036
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] The present invention relates to an offshore platform structure comprising a framework
supporting a platform deck, the framework having at least on leg, and conductor means
for conducting wellbore equipment from the platform deck into at least one wellbore
extending into the earth formation below the platform structure.
[0002] An offshore platform structure of this type is disclosed in GB-B-2000211. The platform
structure is formed of a framework with a leg at each platform corner, the legs being
fixed to the seabed by piles extending through the legs. Conductor conduits extend
from the top of the platform structure through a number of conductor guides into the
seabed. Each conductor conduit consists of a straight, slanted, lower part and a curved
upper part having a vertically extending upper end. Each conductor conduit is installed
by first installing a straight, slanted, conductor, cutting off and removing an upper
part of the straight conductor and replacing this upper conductor part by a curved
conductor part which is welded to the remaining lower straight conductor part.
[0003] Another relevant offshore platform stucture is disclosed in US-A-4,326,595, wherein
a conductor conduit is carried in a cage, which is removably positioned in a platform
leg.
[0004] It is an object of the invention to provide an improved offshore platform structure
which is subjected to reduced environmental loading and has a reduced weight.
[0005] It is a further object of the invention to provide a platform structure having conductor
means which are installed in a less complicated manner.
[0006] In accordance with the invention there is provided an offshore platform structure
comprising a framework supporting a platform deck, the framework having at least one
leg, and conductor means for conducting wellbore equipment from the platform deck
into at least one wellbore extending into the earth formation below the platform structure,
wherein said conductor means includes at least one conductor conduit extending through
said at least one leg.
[0007] To achieve adequate fixation of the conductor conduits, suitably the outer diameter
of each conductor conduit and the inner diameter of the corresponding leg are selected
so that the longitudinal axes of the conductor conduit and the corresponding leg substantially
coincide.
[0008] By locating the conductor conduit within the leg it is achieved that the platform
structure is subjected to reduced wave- and current forces when compared to the conventional
structure, so that the structure can be lighter than the conventional structure. The
conductor conduit can be installed, for example, by driving the conductor conduit
through the leg.
[0009] Preferably the platform structure comprises a plurality of said legs and a plurality
of said conductor conduits, each conductor conduit extending through a corresponding
leg.
[0010] Adequate platform stability is achieved if each conductor conduit which extends through
a corresponding leg provides stability to the platform structure on the seabed by
forming an anchoring pile.
[0011] Enhanced platform stability is achieved by grouting each conductor conduit inside
the corresponding leg.
[0012] The invention will be described hereinafter in more detail with reference to the
appended drawing, in which
Fig. 1 shows schematically a plan view of an embodiment of the offshore platform
structure according to the invention.
[0013] The platform structure shown in Fig. 1 includes a framework 1 with four tubular legs
of which only two legs 5, 7 are shown, the legs being interconnected by a number of
horizontal and sloping braces 11, 11a of which the braces 11a are indicated by dotted
lines as these are located at the side of the framework opposite the plane of the
drawing. Each leg has a curved upper part 12 with substantially constant curvature,
and a substantially straight lower part 14. The upper end 16 of the curved upper part
14 of each leg extends substantially vertically, and the lower part 14 of each leg
extends outwardly in downward direction at a selected inclination angle α.
[0014] A platform deck 18 is arranged on top of the framework 1, the platform deck 18 being
provided with a skid beam arrangement 20 for allowing access of wellbore equipment
to a selected one of a number of conductor conduits described hereinafter.
[0015] The platform structure is provided with four conductor conduits of which only the
two front conductor conduits 22, 24 are shown in dotted lines, each conductor conduit
extending through one of said legs. Thus, in Fig. 1 conductor conduit 22 extends through
leg 5 and conductor conduit 24 extends through leg 7. One of the purposes of the conductor
conduits 22, 24 is to conduct wellbore equipment into wellbores below the platform
structure. To enable conventional drilling rigs to be positioned above all four conductor
conduits, the width of the framework 1 at its upper end is restricted to a dimension
which is equal to or less than the reach of the drill rigs considered for use. Further,
to enable the wellbore equipment to be inserted into the conductor conduits substantially
vertically, the longitudinal axes of the legs at their upper ends 16 extend vertically.
The legs are curved outwardly in downward direction so that the width of the framework
base is sufficient to achieve adequate platform stability. The curvature of the legs
is selected such that conventional wellbore equipment can pass through the legs without
special adaptation. The conductor conduits 22, 24 have been driven from the top of
the platform structure through the respective legs to a selected depth z into the
seabed, for which purpose conventional pile driving techniques can be used. To increase
platform stiffness, the conductor conduits have been fixed in the legs by inserting
grout between each conductor conduit and the corresponding leg. The conductor conduits
22, 24 therefore have the twofold function of conducting wellbore equipment into wellbores
extending from the conductor conduits into the earth formation, and of providing a
structural load bearing capacity in analogy to anchoring piles driven into the seabed.
Furthermore, the conductor conduits provide increased strength to the legs, especially
when the conductor conduits are grouted inside the legs.
[0016] Optionally, additional skirt piles (not shown) can be provided which extend through
skirt pile guides 25 into the foundation so as to increase the resistance against
lateral forces acting on the structure.
[0017] Since the conductor conduits 22, 24 extend through the legs 5, 7 of the framework,
the conductor conduits have substantially the same shape as the legs, i.e. each conductor
conduit 22, 24 has a curved upper part with substantially constant curvature, and
a substantially straight lower part. The upper end 27, 28 of the curved upper part
of each conductor conduit 22, 24 extends substantially vertically, and the lower part
29, 30 of each conductor conduit 22, 24 extends at the inclination angle α in outward
direction relative to the vertical longitudinal axis of the platform structure. Conventional
blowout preventors (BOP's) and /or wellheads 31, 32 are located on top of the upper
ends 27, 28 of the respective conductor conduits 22, 24.
[0018] In a first mode of normal operation of the platform structure of Fig. 1 BOP's 31,
32 are located on top of the upper ends 27, 28 of the respective conductor conduits
22, 24. A drilling rig (not shown) is positioned on the skid beam arrangement 20 vertically
above one of the BOP's, for example BOP 31. A drill string (not shown) extends from
the drilling rig through the BOP 31 and through the conductor conduit 22 into a wellbore
extending from the conductor conduit 22 into the earth formation. The drill string
is rotated so as to deepen the wellbore and to finally reach a hydrocarbon containing
zone in the earth formation below the platform structure. Since the upper end 27 of
the conductor conduit 22 extends vertically there is no need to apply a slanted drilling
rig and a conventional type rig can be used.
[0019] When drilling of the wellbore through conductor conduit 22 is finalised, the drilling
rig is repositioned using the skid beam arrangement 20 in order to place the rig vertically
above BOP 32. The drill string is then inserted into the conductor conduit 24 via
BOP 32 and into another wellbore extending from the conductor conduit 24 into the
earth formation. The drill string is rotated so as to deepen the other wellbore and
to finally reach the hydrocarbon containing zone. This procedure is repeated for the
other two conductor conduits.
[0020] In this manner four wellbores are drilled from the platform structure, which wellbores
extend in outwardly deviating directions due to the outwardly extending lower parts
29, 30 of the conductor conduits 22, 24. At the same time the conductor conduits 22,
24 form anchoring piles which provide stability to the platform structure on the seabed
26.
[0021] In a second mode of operation of the platform structure of Fig. 1, reference signs
31, 32 refer to wellheads which are provided on top of the upper ends 27, 28 of the
respective conductor conduits 22, 24. A production tubing (not shown) extends from
each wellhead 31, 32, through the respective conductor conduit 22, 24, into the respective
wellbore extending downward from the conductor conduit 22, 24. Hydrocarbon fluid is
produced via the production tubing's to suitable production equipment (not shown)
which can be of conventional type.
[0022] Instead of the framework having four legs, the framework can have any other suitable
number of legs and corresponding conductor conduits, for example three or five legs/conductor
conduits.
[0023] Instead of positioning the drilling rig on the skid beam arrangement, the wellbores
can be drilled using a separate jack-up rig having a cantilever deck onto which the
drilling rig is arranged. The jack-up rig is positioned adjacent the platform structure
in a manner that the cantilever deck and the drilling rig are located above the upper
ends of the respective conductor conduits. The wellbores are then drilled from the
jack-up rig. In this mode of operation the skid beam arrangement can optionally be
present on the platform structure.
1. An offshore platform structure comprising a framework (1) supporting a platform deck
(18), the framework having at least one leg (5,7), and conductor means for conducting
wellbore equipment from the platform deck into at least one wellbore extending into
the earth formation below the platform structure, wherein said conductor means includes
at least one conductor conduit (22,24) extending through said at least one leg, characterized in that the outer diameter of each conductor conduit (22,24) and the inner diameter of the
corresponding leg (5,7) are selected so that the longitudinal axes of the conductor
conduit and the corresponding leg substantially coincide.
2. The platform structure of claim 1, comprising a plurality of said legs and a plurality
of said conductor conduits (22,24), each conductor conduit extending through a corresponding
leg (5,7).
3. The platform structure of claim 1 or 2, wherein each leg (5,7) is of tubular shape
and extends from the platform deck (18) to the seabed.
4. The platform structure of any of claims 1-3, wherein the upper end of each leg (5,7)
extends substantially vertically and the lower end of the leg extends outwardly in
downward direction at a selected inclination angle.
5. The platform of claim 4, wherein an upper end part of each leg has a selected curvature,
and wherein a lower end part of the leg is substantially straight.
6. The platform structure of any of claims 1-5, wherein each conductor conduit (22,24)
is grouted inside the corresponding leg (5,7).
7. The platform structure of any of claims 1-6, further comprising a skid beam (20) arrangement
provided at said platform deck (18) for allowing access of the wellbore equipment
to a selected one of the conductor conduits (22,24).
8. The platform structure of any of claims 1-7, wherein the structure includes at least
one skirt pile connected to the framework (1) and extending into the seabed.
1. Eine Offshore-Plattformstruktur mit einem Rahmen (1), der ein Plattformdeck (18) trägt,
wobei der Rahmen zumindest ein Bein (5, 7) und Führungsmittel zum Führen einer Bohrlochausrüstung
von dem Plattformdeck in zumindest ein Bohrloch aufweist, das sich unterhalb der Plattformstruktur
in eine Erdformation erstreckt, wobei die Führungsmittel zumindest ein Leitungsrohr
(22, 24) aufweisen, das sich durch das zumindest eine Bein erstreckt, dadurch gekennzeichnet, daß der Außendurchmesser jedes Leitungsrohres (22, 24) und der Innendurchmesser des entsprechenden
Beines (5, 7) so gewählt sind, daß die Längsachse des Leitungsrohres und des entsprechenden
Beines im wesentlichen koinzidieren.
2. Plattformstruktur nach Anspruch 1 mit einer Vielzahl von Beinen und einer Vielzahl
von Leitungsrohren (22, 24), wobei sich jedes Leitungsrohr durch ein entsprechendes
Bein (5, 7) erstreckt.
3. Plattformstruktur nach Anspruch 1 oder 2, bei welcher jedes Bein (5, 7) rohrförmige
Gestalt hat und sich vom Plattformdeck (18) zum Meeresboden erstreckt.
4. Plattformstruktur nach einem der Ansprüche 1-3, bei welcher sich das obere Ende jedes
Beines (5, 7) im wesentlichen vertikal erstreckt, und sich das untere Ende des Beines
in Richtung nach unten unter einem vorbestimmten Neigungswinkel auswärts erstreckt.
5. Plattform nach Anspruch 4, bei welcher ein oberer Endteil jedes Beines eine vorbestimmte
Krümmung hat, und bei welcher ein unterer Endteil des Beines im wesentlichen gerade
ist.
6. Plattformstruktur nach einem der Ansprüche 1-5, bei welcher jedes Leitungsrohr (22,
24) innerhalb des entsprechenden Beines (5, 7) eingemörtelt ist.
7. Plattformstruktur nach einem der Ansprüche 1-6, die ferner eine Gleitträgeranordnung
(20) aufweist, die am Plattformdeck (18) vorgesehen ist, um einen Zutritt der Bohrungsausrüstung
zu einem vorbestimmten Leitungsrohr (22, 24) zu gestatten.
8. Plattformstruktur nach einem der Ansprüche 1-7, bei welcher die Struktur zumindest
einen Mantelpfahl aufweist, der mit dem Rahmen (1) verbunden ist und sich in den Meeresboden
erstreckt.
1. Structure de plate-forme marine comprenant une charpente (1) supportant un pont en
plate-forme (18), la charpente comportant au moins un montant (5, 7) et un moyen de
guidage pour guider un équipement de puits de forage du pont en plate-forme dans au
moins un puits de forage s'étendant dans la formation terrestre en dessous de la structure
de plate-forme, dans laquelle ledit moyen de guidage comprend au moins un conduit
de guidage (22, 24) s'étendant dans au moins le montant précité, caractérisée en ce que le diamètre extérieur de chaque conduit de guidage (22, 24) et le diamètre intérieur
du montant correspondant (5, 7) sont choisis de telle sorte que les axes longitudinaux
du conduit de guidage et du montant correspondant coïncident sensiblement.
2. Structure de plate-forme suivant la revendication 1, comprenant une pluralité des
montants précités et une pluralité des conduits de guidage (22, 24) précités, chaque
conduit de guidage s'étendant dans un montant correspondant (5, 7).
3. Structure de plate-forme suivant l'une ou l'autre des revendications 1 et 2, dans
laquelle chaque montant (5, 7) est de forme tubulaire et s'étend du pont en plate-forme
(18) au fond de mer.
4. Structure de plate-forme suivant l'une quelconque des revendications 1 à 3, dans laquelle
l'extrémité supérieure de chaque montant (5, 7) s'étend sensiblement verticalement
et l'extrémité inférieure du montant s'étend extérieurement vers le bas suivant un
angle d'inclinaison choisi.
5. Plate-forme suivant la revendication 4, dans laquelle une partie d'extrémité supérieure
de chaque montant présente une courbure choisie, et dans laquelle une partie d'extrémité
inférieure du montant est sensiblement droite.
6. Structure de plate-forme suivant l'une quelconque des revendications 1 à 5, dans laquelle
chaque conduit de guidage (22, 24) est cimenté à l'intérieur du montant correspondant
(5, 7).
7. Structure de plate-forme suivant l'une quelconque des revendications 1 à 6, comprenant
de plus un agencement de poutrelles coulissantes (20) prévues au pont en plate-forme
(18) précité pour permettre l'accès de l'équipement de puits de forage à un des conduits
de guidage (22, 24) choisi.
8. Structure de plate-forme suivant l'une quelconque des revendications 1 à 7, dans laquelle
la structure comprend au moins une pile additionnelle périphérique reliée à la charpente
(1) et s'étendant dans le fond de mer.