Note: Descriptions are shown in the official language in which they were submitted.
. CA 02318990 2000-07-24
WO 99/38763 PCT/N099/00020
A~1 ARRANGEMENT FOR A DRILL1NGIPRODUCTION
VESSEL WITH GEOSTATIONARY ANCHORING
Several proposed arrangements for drilling for oil and gas from production
ships are
s known. These arrangements can be put into several categories, and there are
three main
categories.
According to the first category, drilling takes place with the aid of
conventional
dynamically positioned or firmly moored drilling ships which are also equipped
with
~ o brackets for the suspension of risers, preferably on the outside of the
hull.
It is typical for this category that the arrangement solutions are used in
areas where
weather conditions are more moderate, and where the ship basically can lie in
a fixed
direction which is co-linear with the dominant wind direction. The ship may be
firmly
~ s moored or based on dynamic positioning, a solution particularly relevant
where great
ocean depths are involved.
According to a second category, drilling takes place from a ship having a
geostationary
turret with production risers, and where the drilling centre is positioned
outside the
2o turret.
Such ships are also normally intended for use in areas where weather
conditions are
moderate, as they are chiefly meant to use the drilling package only when the
ship is
able to lie in certain fixed directions.
2s
A third category in one wherein drilling is carried out from ships having
geostationary
turrets with production risers, and where the drilling takes place centrally
in the turret.
An arrangement of this kind has the best potential for use in more exposed
3o environments, such as the North Sea, west of Shetland and the Norwegian
Sea. With
this arrangement a ship can drill irrespective of the direction from which the
forces of
wind and weather come, and can adjust its position to the direction which
gives least
motion for the drilling operation. Thus far, no combined drilling/production
ship having
such an arrangement has been built, but information regarding several versions
has been
3s published. A recurrent feature in the proposed arrangements in that they
are largely
based on existing turret solutions for pure production purposes.
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WO 99/38763 PCT/N099/00020
2
A typical and well J~nown solution in the last-mentioned category is to place
the derrick
and drill floor up on the actual turret, so that the drilling system is
geostationary
together with the moorings and the risers. Because it is then possible to use
a swivel
solution to transfer the production from the riser to the ship's deck, a
transfer system in
the form of a chain, referred to hereinafter for the sake of simplicity as
"drag chain",
which is located on and supported by the turret, is employed instead. Of
course, this
means that the actual turret will be large in size and will have great bearing
forces, with
the turret's own weight, mooring equipment and forces, riser weight and
forces, the
weight of the drag chain and the drilling package with hook load and riser
forces all
~o contributing.
One problem with an arrangement of this kind is that the drill floor
constantly changes
direction, so that pipe handling becomes problematic. Similarly, the supply of
drilling
mud from high-pressure pumps on the deck represents a problem (must go in the
drag
~ s chain), whilst the return mud is a little easier to handle.
A related and somewhat improved variant of the last-mentioned arrangement is
to lift
the drilling package off the turret and support it directly from the ship's
deck by means
of a separate support structure. The gain here is that the turret is relieved
of the
2o associated loads, and that it becomes considerably easier to arrange the
drilling mud
process {as on a conventional exploration rig).
Nevertheless, the same problem remains as with the arrangement where the
derrick and
drill floor are arranged on the actual turret, namely the elevated height of
the structure,
2s the weight of the drag chain, and problems of clearance for the risers in
the so-called
moonpool, i.e., the vertical opening in the turret. The elevated height of the
structure is
due to the fact that the blow-out preventer (BOP) must be handled at a level
above the
drag chain, preferably at an upper turret level, and that the drill floor and
derrick will be
positioned many metres (as a rule about 15 metres) above this level. The high
level of
3o the drill floor causes problems as regards centre of gravity and not least
as regards the
clearance in the turret opening for the risers.
The invention relates to an arrangement of the last-mentioned type, and the
object of the
invention is to provide a new and improved arrangement for a combined
3s drilling/production ship of the last-mentioned category.
CA 02318990 2000-07-24 ~~ ~~9 (~ (~(?~~
'~ p ~ -02 2000
Pa a 2a
US 4762185 A shows an arrangement for handling drill string elements on an off
shore
drilling rig. A ring-like structure with circular inner and outer walls around
a central drill
axis forms a storage space which can be divided into compartments for vertical
storage
of drill string elements, and other drilling equipment such as a B.O.P. There
is an access
opening for B.O.P. to the central drill axis from its storage position.
NO C 166497 shows a turret construction on a production vessel where one or
more
flexible hoses for transfer of production from the riser to the ship's deck
are laid over a
vertical wheel which is pivotable about a horizontal axis and attached to a
frame attached
to the turret and arranged to roll on a track on the ships deck. This drag
chain
construction gives free access to a circumferential section of the cylindrical
structure of
the turret.
US 4692081 A shows a ring-like drill string storage under the drill floor with
cylindrical
inner and outer walls for vertical storage of drill string elements, where the
inner wall
circumscribes a moon pool.
US 4063650 A shows a transporter system for handling heavy equipment, e.g. a
B.O. on
floating type drilling vessels. The B.O.P. is transported along a track.
CA 02318990 2000-07-24 P~ I, NU 9 9 ~ 0 0 ~ 2 0
Amended pages 3 and 4
According to the invention, an arrangement is proposed for a
drilling/production vessel
having geostationary anchoring, including a turret in the form of a
substantially hollow
cylindrical body, which turret is pivotally supported about a vertical axis in
a vertical
through opening in the vessel,
a vessel-supported drill floor above the turret,
guides means for risers in the turret, and
a drag chain for the transfer of production from the risers to a deck on the
vessel,
characterised by a vertical pipe rack incorporated in a cylindrical structure
coaxial with
the turret and which extends down from the drill floor and into the through
opening in
the turret,
a lateral access opening in the vertical pipe rack on a level with the drag
chain, and
the drag chain includes a support structure which extends around the
circumference of
the rotating part, said support structure having a removable circumferential
section
opposite the lateral access opening, or
that the drag chain only extends along a part of the circumference of the
turret, so that
the lateral opening is freely accessible from the vessel's deck when the
vessel is lying in
its dominant wind direction.
The drill floor is supported on the vessel's deck at such a height as to
enable a BOP or
other largish equipment units to be manoeuvred from the vessel's deck and into
the
turret through the lateral opening. If the blow-out preventer is to be capable
of being
brought inside the turret, the drag chain must not block the lateral opening.
Such
clearance is in theory completely possible by locating the starting point of
the drag chain
on the side of the turret and the end point of the drag chain on the deck of
the vessel so
that in a particular sector or particular circumferential section it is
possible to cross the
drag chain track when the vessel is lying in the dominant wind direction. The
lateral
access opening can also be cleared by breaking a circumferential area of the
drag chain,
i.e., its utilised support structure, naturally on the condition that the drag
chain (the
pipes) are not in this area in the particular vessel orientation.
The new arrangement is also especially distinctive because the volume or space
below
the drill floor is used for vertical storage of pipes, such as risers for
drilling arid drill
AMENDED SHEET
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PC~~Ivo99 / d DD~
0 4 -02- 2000
pipes. As this vertical pipe rack is suspended from the drill floor or the
drill floor
support structure, the pipe rack will be stationary relative to the vessel and
to the drill
floor that is stationary relative to the vessel.
An especially preferred embodiment of the arrangement according to the
invention is one
wherein the drag chain is "inverse", i.e., that it is supported by and moves
on the vessel's
deck, an inner part of the chain following the movement of the turret, whilst
the outer
part rests on the vessel's deck. This means that the inner part of the drag
chain will
follow the movement of the turret, and move relative to the vessel's deck
(scrubber),
whilst the outer part of the drag chain rests on the deck of the vessel.
In a "normal" and known embodiment of the drag chain, the drag chain is
positioned on
the actual turret and is set in motion with the aid of a securing structure
(derrick) which
projects up from the vessel's deck with fixed piping.
An especially favourable arrangement is obtained if the "bull nose" of the
drag chain, i.e.,
the drag chain's turning arrangement includes a planet wheel unit which has
driving
engagement with the turret (sun wheel) and with a rotating drive ring in the
vessel, direct
or via the drag chain. A rotating bull nose of this kind will cause a
"lifting" of the chain
from the ship's deck and will place it on the turret. The planet wheel will to
advantage
be made so that the engagement with the chain is synchronous will the chain's
travel
from inner to outer track and vice versa, i.e., the same radius for the planet
wheel as the
turning radius of the chain. In this way, chain movement friction against the
underlying
surface will be avoided. In all positions, the drag chain will rest against
the underlying
surface, if the transverse movement which takes place when the chain enters
and exits the
planet wheel is disregarded.
The planet wheel solution will be especially advantageous if it is used
simultaneously for
dynamic braking of the turret relative to the orientation of the ship. Safety
is increased
considerably by controlling the planet wheel.
AMENDED SHEET
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A substantial redu~ion in capacity for operating the turret is obtained if the
procedure is
based on the use of forces (moment) from moorings and risers to turn the
turret. This
can be achieved by fuming the ship actively with the aid of thrusters 7 -
15° beyond the
desired turning. As the angle of friction is reached, a controlled movement
will be
s obtained.
On the deck of the vessel there may to advantage be arranged a trackway
leading in
towards a lateral opening for transport of the blow-out preventer. This
trackway
intersects the drag chain path and runs towards a lateral opening in the
turret for a
~ o particular vessel orientation. The trackway may, for example, be made as a
recessed
track which meets similar tracks in the turret. Inside the actual turret, a
transport trolley
running on the trackway will be capable of rolling onto tracks which are
suspended in
the support structure of the drill floor, so that the transport of the blow-
out preventer can
take place in the very centre of the turret, at the so-called cellar deck
level. Here, the
~ s blow-out preventer (BOP) will be capable of being suspended from the drill
floor and
lowered down through the moonpool to the seabed by means of a drill/riser.
The planet wheel unit may to advantage be incorporated in a carriage, which
carnage is
moveable in a guide track around the turret.
In the carriage there may be provided two motors, each of which is drive-
connected to a
respective gear wheel which is in engagement with the turret or the rotating
drive ring in
the vessel.
2s Furthermore, a curved redirecting plate for the drag chain may to advantage
be provided
in the carriage.
The guide track is constructed as a type of circumferential trench and it can
advantageously be covered by a grating or the like which is attached to the
carriage.
The particular advantage obtained with the new arrangement according to the
invention
is a reduction in structural height, because the BOP can be brought in on the
level of the
vessel's deck. At the same time, the space under the drill floor is used in an
expedient
manner for a vertical pipe rack that is stationary relative to the drill
floor.
3s
The invention will now be explained in more detail with reference to the
drawings,
wherein:
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WO 99/38763 PCTIN099/00020
6
Fig. 1 is a perspective view of an arrangement according to the invention;
Fig. 2 is a perspective view of the arrangement in Fig. 1, from the opposite
side;
Fig. 3 is a perspective view of a second feasible embodiment of the
arrangement
s according to the invention, seen from the same side as in Fig. 2;
Fig. 4 is a schematic horizontal projection of the arrangement according to
Figs. 1 and
2;
Fig. 5 is a schematic horizontal projection of the arrangement according to
Fig. 3;
Fig. 6 is a cross-sectional view of a vessel equipped with an arrangement
according to
~o the invention as in Fig. 1;
Fig. 7 is a schematic section of a planet wheel unit used in the embodiment of
Figs. 1, 2
and 4.
Fig. 8 is a schematic horizontal projection of an arrangement according to the
invention,
with a planet wheel unit carriage;
i s Fig. 9 is a schematic sectional view through the rail area in the system
in Fig. 8;
Fig. 10 is a schematic longitudinal sectional view through a planet wheel unit
carriage;
Fig. I I is a schematic horizontal projection of the carriage illustrated in
Fig. 10;
Fig. 12 is a cross-sectional view through the carnage;
Fig. 13 is a schematic horizontal projection of a modified planet wheel
embodiment;
2o and
Fig. 14 is a schematic sectional view as in Fig. 7, of the modified embodiment
shown in
Fig. 13.
The same reference numerals have been used in the drawings for the same or
2s corresponding components in the two embodiments.
Figs. I, 2 and 4 show a section of a vessel I having a deck 2. In the vessel 1
there is a
vertical through opening 3 (see Fig. 6) where in a known manner there is
arranged a
turret 4. The turret 4 is made in the form of a hollow cylindrical body having
an upper
3o annular flange 5.
The vessel 1 is constructed having a hull that can take a large vertical
opening 3, and the
turret 4 on its part is equipped with a through opening or moonpool 6 which is
as Iarge
as possible, so that it will not come into conflict with a drilling operation.
The through
3s opening 6 in the turret can without any difficulty be made so large that,
for example, a 9
- 10° deviation of the drilling riser (not shown) will be allowable
without coming into
contact with the inner wall of the turret. In the exemplary embodiment, the
turret is
CA 02318990 2000-07-24
WO 99/38763 PCT/N099100020
7
constructed as a hollow cylinder with a solid casing, but the turret may also,
for
example, be constructed as illustrated and described in Norwegian Patent
Application
P970508.
s A support structure 7 for a drill floor 8 is provided on the deck 2 of the
vessel. The
support part 7 in this case has three legs 9, 10 and 11. This gives a stable
structure with
plenty of space between and on the inside of the support legs 9, 10, I 1.
A rig or derrick 12, here only indicated schematically, extends upwards from
the drilling
~ o deck 8.
A cylindrical structure 13 extends down from the underside of the drill floor
8. This
cylindrical structure 13 extends down to the deck 2 of the vessel and
advantageously
some way down into the moonpool 6, as is shown in Fig. 6. The cylindrical
structure 13
is is open at the top and made in the form of a vertical pipe rack 14. To
illustrate this
some pipes I S placed vertically in the pipe rack 14 have been indicated in
Figs. 1 and 6.
The pipe rack 14 takes up quite a large part of the circle, and in the centre
there is an
open space under the drill floor 8, for the carrying out of drilling
operations and also for
the lowering of necessary equipment, and especially the so-called blow-out
preventer or
2a BOP.
Here, the cylindrical structure 13 is shown for the sake of simplicity with a
solid casing
wall, but the structure may of course be made as a truss construction.
Regardless of the
casing embodiment, in the vertical pipe rack there is provided a laterally
directed access
2s opening 16 on a level with the vessel's deck 2. A BOP can be passed in
through this
opening 16 from the vessel's deck 2 and into the space under the drill floor
8, for
lowering to the seabed.
In the turret 4 there are provided conductor casings 17 (see Fig. 6) for non-
illustrated
so production riser 18 (see Fig. 1 ). These production risers 18 run up to
valves 19 on the
upper annular flange 5 of the turret. For the transfer of the production from
the turret to
the vessel a drag chain is used which consists of a pipe transfer system in
the form of a
chain and which is known in the industry as a drag chain. A drag chain 20 of
this kind
is indicated in Figs. 1, 2, 4 and 6. The illustrated drag chain 20 extends as
shown along
3s a part of the circumference of the turret and is arranged so that in the
dominant wind
direction of the vessel the side opening 16 will be freely accessible, as can
be seen in
particular from Figs. 2 and 4.
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8
The drag chain's so-called bull nose or chain nose is advantageously provided
with a
special planet wheel unit 21, shown in a schematic section on a larger scale
in Fig. 7.
The planet wheel unit 21 is positioned as a turning arrangement for the pipes
22 in the
s drag chain. In this case, the planet wheel unit 21 includes three gear
wheels 23, 24 and
25. The two upper gear wheels 23, 24 have respective driving engagement with
respectively the upper and lower elements 26, 27 of the drag chain. The lower
gear
wheel 25 has driving engagement with a gear rim 28 on the turret 4, 5 and an
outer
annular gear rim 29 which is attached to the vessel 1. Thus, in this case the
turret 4, S
~o functions like a sun wheel, whilst the gear wheel 25 functions as a planet
wheel. This
planet wheel unit thus forms the so-called "bull nose" or chain nose of the
drag chain.
When the rotating part 4 rotates relative to the ship 1, the chain nose or
planet wheel
unit 21 will also be rotationally actuated and will "lift" the chain from the
ship's deck 2
and over onto the turret, i.e., the track formed in the annular flange 5 of
the turret. In
~ s this way motional friction against the underlying surface is avoided,
because the drag
chain will rest constantly against the underlying surface, apart from the
transverse
movement which takes place when the chain enters/exits the planet wheel.
In Fig. 7 roller bearings 30, 31 are provided for the turret 4, 5, whilst
upper guide rails
20 32 for the drag chain 20 are indicated.
It will be appreciated at once that the arrangement in Figs. l, 2, 4 and 6
gives free access
to the opening 16 in the vessel's dominant direction, i.e., when the ship is
lying in the
dominant wind direction (that is calculated beforehand), so that a BOP can be
brought in
zs under the drill floor 8 with the aid of a non-illustrated trolley which
runs on the
indicated trackway 33.
In Figs. 3 and 5 it is shown how access to the side opening 16 can be obtained
in those
cases where the choice has been made to use a conventional drag chain 35. The
drag
3o chain 35 has in a known manner an inner and encompassing support structure
36, here
only shown schematically, which extends around the whole circle. In Figs. 3
and 5, the
so-called "bull nose" is indicated by means of the reference numeral 37. The
drag chain
35 will not be described in more detail here as it is a well-known device.
What is
essential here is that a portion 38 of the support structure 36 (both inner
and
3s encompassing) can be taken away or removed when the vessel is lying in the
dominant
wind direction, so that access to the side opening 16 is thus cleared and a
BOP can be
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WO 99/38763 PCT/N099/00020
9
moved into the spaee below the drill floor 8, for example, with the aid of a
trolley which
runs on the rails 33.
One embodiment of the invention, where the planet wheel unit is incorporated
in a
s carriage is shown in Figs. 8-12.
This carnage 40 is shown schematically in Figs. 10, 11 and 12. In essence, the
carriage
40 is constructed having a bottom plate 41 and a top plate 42. The planet
wheel unit 21
is pivotally mounted in the top plate 42 and the bottom plate 41. In the
vessel 1 there is
~ o around the rotating part 4, S provided an encompassing trench 43 as guide
track for the
carriage. As in the embodiment in Fig. 7, there is provided in the trench a
gear rim 28
on the rotating part 4, 5 and an outer annular gear rim 29 attached to the
vessel 1. The
planet wheel unit 21 also includes in this case gear wheels 23, 24 in
engagement with
gear rims 26, 27 in the drag chain 20. Furthermore, the planet wheel unit has
a lower
i s gear wheel in engagement with gear rims 28 and 29, see Fig. 12.
In the carnage 40 there are provided two motors 44, 45 which are drive-
connected to a
respective drive or gear wheel 46, 47 which has driving engagement with
respectively
the gear rim 28 on the turret S and the gear rim 29 on the side of the vessel
(see Figs. 10
2o and 11 ).
Support structures 48, 49 for the drag chain 20 are indicated in Fig. 12.
As shown in Figs. 10 and 1 l, a curved redirecting plate 50 for the drag chain
20
2s (indicated by means of a broken line in Figs. 10 and 11 ) is provided in
the carriage.
The motors 44, 45 are used essentially as a brake to control the rotational
speed of the
turret 4, 5 in the vertical opening, and also for locking the turret.
3o A driving mechanism 66 for the turret 4, 5 is ship-mounted and indicated in
broken lines
in Fig. 8. In an arrangement with planet wheels there will be a sector of
90° where a
drive wheel will not come into conflict with the planet wheel.
Advantageously, there is provided, for example, a grating or grid-like deck
surface
3s structure 51 over the trench 43, see Figs. 8 and 9. As shown, this grating
is expediently
divided into sections 52-58 which are hingedly interconnected 59 and are also
hingedly
connected 60, 61 to the carnage 40. The carriage 40 in the schematic view in
Figs. 10
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WO 99/38763 PCT/N099100020
and 11 is shown hawing a rectangular form in horizontal projection, but the
carriage 40
will in practice have the sector shape shown in Fig. 8.
A track 33 runs from the vessel 1 and into the rotating part, for the
introduction of a
s BOP as described above. Supplementary rails are inserted in the open short
rail sections
62, 63 and 64, see Fig. 9, when the track 33 is to be used.
As indicated in Fig. 9, the grating 51 is supported by suitable rollers 65 in
the guide
track or trench 43. The grating 51 can be made to maintain the form of the
drag chain in
i o its lower part, and this will largely ensure that the whole chain in the
vertical plane
maintains the desired form and stability.
Figs. 13 and 14 show how the planet wheel unit 21 can have indirect driving
interaction
with respectively the outer annular gear rim 29 attached to the vessel 1 and a
gear rim
~s 28 on the turret 4, 5, wherein a lower part of the drag chain 20 is in
engagement with the
annular gear rim 29 and the gear rim 28, and at the same time has driving
engagement
with a lower gear wheel 25' in the planet wheel unit. The respective gears 46,
47 also
have indirect driving engagement via the drag chain.
2o Today's drag chains have inter alia a lower chain section wherein the chain
links are
hinged centrally. This must therefore be taken into account (the distance
between the
links diminishes in the "inner swing" when the chain runs in a curve around
the planet
wheel) when forming the teeth on the planet wheel, or the drag chain (its
hinging) must
be modified accordingly.
The invention provides a crucial advantage, namely that heavy and high
equipment, and
in particular a blow-out preventer (BOP) can be moved in on a level with the
vessel's
deck 2. This brings about a possibility for lowering the centre of gravity of
the whole
arrangement, with accompanying improved stability of the vessel.
It is also an advantage that a very expedient vertical pipe rack is provided
which is
stationary relative to the drill floor. A vertical pipe rack of this kind
facilitates the
handling of the pipes to and from the rack.
ss The whole arrangement allows drilling to take place from the ship's weather
deck or
main deck in the same way as drilling from the deck of a semi-submersible
platform,
CA 02318990 2000-07-24
WO 99138763 PCTIN099I00020
11
i.e., with the brackgt joints of the riser just below the drill floor with
underlying
telescopic joints and with a good clearance from risers to other parts of the
hull.
