Note: Descriptions are shown in the official language in which they were submitted.
CA 02252787 2004-12-02
SLIP JOINT
The present invention relates to a slide joint for a riser between a well and
a floating
petroleum installation, for example, an oil platform, comprising an outer pipe
and an
inner pipe, which pipes are adapted to move telescopically relative to one
another to
compensate for changes in the distance between the sea bed and the platform.
A known slide joint of this type is shown in Figure I . To maintain tension in
the riser,
a plurality of wires are attached to the upper end of the outer pipe, which
wires in turn
are connected to a plurality of tensioners, which exert a constant tension on
the riser.
The wires, tensioners, appurtenant collection reels and other equipment
associated
with the tensioning apparatus for the riser require considerable space and, in
addition,
are very heavy. Moreover, the wires are under substantial strain and must be
inspected and changed relatively often.
The object of the present invention is to replace the wires, tensioners and
collection
reels, as well as the other equipment connected thereto, with far simpler and
lighter
equipment requiring less space. It is also an objective to provide a slide
joint having
I S improved functional efficiency and greater reliability.
Specifically according to this invention there is provided a slide joint for a
riser
between a well and a floating petroleum installation comprising an outer pipe
and an
inner pipe, which pipes are adapted to move telescopically relative to one
another to
compensate for changes in the distance between the sea bed and the platform,
where
the inner pipe at or near the downward oriented end thereof is fixedly
connected to a
piston, which piston is responsive to actuation by hydraulic pressure in order
to
provide tractive force on the riser, and where there is formed between the
inner pipe
and the outer pipe a first annulus, which is isolated from both the well fluid
and the
surrounding atmosphere, said itr5t aiiuuius auovc tiic p%JlVll bGlllg
slAbJclited tV
hydraulic pressure, characterized in that a protective sleeve is slidably
disposed within
the outer pipe below the piston, which protective sleeve is pressure actuated
to make
contact with the lower end of the inner pipe whereby another annulus, formed
between the protective sleeve and the outer pipe, is subjected to a preferably
constant
pressure in order to seal off the piston against contact with well fluid, and
that the
protective sleeve is provided with an upper piston, the annular area of said
upper
piston toward the second annulus being greater than the annular area of the
upper
CA 02252787 2004-12-02
1-A
leakage of fluid past the upper piston occurs in the direction from the second
annulus
to the third annulus on the opposite side of the upper piston and that the
outer pipe is a
two-part structure, so that it may be divided into an upper and a lower
section, where
the inner pipe is accommodated in the upper section, and the protective sleeve
is
accommodated in the lower section.
This is achieved by connecting the inner pipe to a piston, which piston is
responsive
to actuation by hydraulic fluid to provide tractive force on the riser.
This apparatus enables savings in equipment weight in the magnitude of 100
tons,
which is a considerable weight even on a large oil platform. The equipment is,
moreover, far less demanding in terms of space and provides increased
functional
efficiency in that the riser is able to swing freely in the vertical plane
without
obstruction by taut wires. The tractive force exerted on the riser is entirely
axial, thus
avoiding the incidence of adverse lateral forces on the riser. Maintenance is
also
simplified considerably, for the only components that must be replaced
frequently are
the hydraulic hoses. There is a double set of hydraulic hoses, permitting the
changing
of these hoses one by one without having to shut down the system.
The invention shall now be described in more detail with reference to the
accompanying drawings, wherein:
Fig. 1 shows a slide joint according to the known technique,
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Fig. 2 shows a slide joint according to the invention,
Fig. 3 shows the slide joint in more detail,
Fig. 4 shows the riser with the slide joint in even greater detail,
Figs. Sa-Sf show sections of various parts of the slide joint and the riser,
and
~o Fig. 6 is a schematic view of the invention's hydraulic system.
Fig. 1 shows a slide joint 1 in accordance with the prior art. Slide joint 1
consists of an
inner pipe 2 and an outer pipe 3. Outer pipe 3 is connected to the rest of the
riser 4,
which extends down into the well (not shown). Outer pipe 3 is provided at the
upper
i s end thereof with a collar S to which is connected a plurality of wires 6,
which in turn are
connected to tensioners 7. There are also provided collection reels 8 for
wire. The inner
pipe is connected via a flexible coupling 9 to the production equipment on the
platform
(not shown). In Fig. 1 there are also shown two hoses, which are connected via
ducts in
riser 4 with the BOP, one of these hoses being adapted to throttle the return
from the
2o well, while the other hose is adapted for pumping kill mud down into the
well.
In Fig. 2 a slide joint 10 in accordance with the invention is shown. The
slide joint here
also consists of an inner pipe 11 and an outer pipe 12. Inner pipe 11 is here
also
connected to the platform's production equipment via a flexible coupling 13.
Here,
is however, the slide joint is attached to hydraulic accumulators 14 which,
via hydraulic
hoses 1 S, supply hydraulic pressure to slide joint 10, causing riser 16 to be
placed under
tension.
Fig. 3 shows the slide joint in more detail. Here we also see inner pipe 11,
outer pipe 12
3o and flexible coupling 13. Hydraulic hoses 1 S are attached to a manifold
ring 17, which
is connected to the upper end of outer pipe 12. In Fig. 4 the riser and slide
joint 10 are
shown in a position that is swung out l oo to the side. This outward swing is
permitted
without the hindrance of wires or other equipment. The slide joint is
therefore capable
of swinging outward until it is in quite close proximity to the edge of the
moon pool 18.
In Fig. 5 the slide joint is shown in even more detail. Outer pipe 12 consists
of two
parts, an upper part 19 and a lower part 20, which are joined together by a
flange
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3
connection 21. The outer lower pipe 20 has an internal bore which is narrowed
at its
lower end 22.
Figs. Sa-Sf shall now be described. Fig. Sa is a cross-section of the upper
end 23 of the
s outer pipe, and shows a section of inner pipe 11 and outer pipe 12. At the
upper end 23
of outer pipe 12 is mounted a packer 24 which forms a seal between the
internal surface
of outer pipe 12 and the external surface of inner pipe 11. Beneath packer 24
the
manifold ring 17 is in hydraulic communication with annulus 25 between inner
pipe 11
and outer pipe 12 via an automatic shutoff valve 26.
~o
Fig. Sb shows a section of the slide joint at the lower end of inner pipe 11.
Here we see
a piston 27, which is connected to inner pipe 11. Piston 27 is sealed against
the internal
surface of the outer pipe by means of a packer 28. Annulus 25 is thus
isolated, except
for the hydraulic communication with hoses 15. In Fig. Sb is also shown the
upper end
is of a protective sleeve 29, which is provided with a combined packer and
piston 30
which forms a seal against the internal surface of outer pipe 12. In Fig. Se
this packer is
shown in more detail. Packer 30 does not form a complete seal against the
internal
surface of outer pipe 12, but permits a slight leakage from annulus 31, which
is formed
between protective sleeve 29 and outer pipe 12, and in addition a slight
leakage between
2o protective sleeve 29 and piston 27 to boring 32, for the transport of mud
and petroleum
products. The reason for this slight leakage will be explained later. Fig. Sc
shows a
section of outer pipe 12 at its flange connection 21 between the upper part 19
and the
lower part 20, and also shows a section of protective sleeve 29 a slight
distance below
the upper end thereof. Outer pipe 12 is here provided with a packer 33, which
is shown
2s in more detail in Fig. Sf. Packer 33 forms a seal against protective sleeve
29. Directly
above packer 33 is provided a passage 34 for supply of pressure medium, for
example
air or water, to permit the pressurizing of annulus 31. This will also be
explained later.
Fig. Sd shows a section near the lower end of outer pipe 12 and a section from
the lower
end of the protective sleeve. Here we see that outer pipe 12 becomes narrower
at 35.
3o Protective sleeve 29 is provided at the lower end thereof with a guide and
scrape ring
36, which has an external diameter that is larger than the smallest diameter
of outer pipe
12 at 35.
When hydraulic pressure is supplied via hoses 15 to annulus 25 between inner
pipe 11
3s and outer pipe 12, the inner pipe and the outer pipe will telescopically
slide together.
Riser 16 is thereby placed under tension. The tension may be regulated by
increasing or
lowering the hydraulic pressure. For work at greater sea depths, with a riser
that is
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4
altogether relatively heavy, a much higher pressure will be required than with
a riser
employed at lesser sea depths.
To avoid the possibility that mud, petroleum products or tools, such as drill
heads or the
s like, will scrape up or otherwise damage the internal surface of outer pipe
I2, such that
piston 28 is no longer able to slide without difficulty along the internal
surface of outer
pipe 12, the protective sleeve 29 is provided in order to protect the internal
surface of
outer pipe 12. With the aid of fluid supply through passage 34, protective
sleeve 29 is
held at all times in contact against piston 28. The pressure supplied to
annulus 31
~o through passage 34 is preferably constant. The permitting of a slight
leakage past
packer 30 ensures that mud or petroleum products will not be able to penetrate
into
annulus 31. Protective sleeve 29 is so long that its lower end provided with
scrape ring
36 will never move above the lowermost position for piston 28.
~s Fig. 6 shows the hydraulic system. Here we also see slide joint 10 with
inner pipe 11
and outer pipe 12. Protective sleeve 29 is also shown. A pump 37 delivers air
to a
plurality of air tanks 38. One of the air tanks functions as a stand-by
pressure tank 39
and at all times places at disposal a pressure of 210 bar for those instances
when inner
pipe 11 must be moved rapidly relative to outer pipe 12. The tanks 38, 39 are
connected
2o to accumulators 40 via a valve 41. A valve 42 is also installed between
tank 39 and the
other tanks 38. Accumulators 40 are connected with annulus 25 via hydraulic
hoses 1 S
equipped with an automatic shutoff valve 26 at each end.
Further, there is provided a pressure tank 43 which, via a hose 44, places
annulus 31
zs under a moderate pressure in order to maintain the contact of protective
sleeve 29
against inner pipe 11.
During normal operation the pressure in tanks 38 may vary between 20 and 210
bar,
according to the particular speed at which slide joint 10 must move and to the
3o magnitude of the forces that occur. When necessary, however, a pressure of
210 bar in
tank 39 is available.
The section in Fig. 6a illustrates a somewhat different embodiment of the
connection
between protective sleeve 29 and inner pipe 11.
Protective sleeve 29 could have been fixed permanently to inner pipe 11, but
this would
make more difficult the handling of the slide joint during both transport and
installation.
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Since outer pipe 12 is divided into two parts, 12 and 20, the outer pipe may
be divided
at flange coupling 21. When this is done, one must ensure that protective
sleeve 29 is
situated within the lower part 20, at the same time as inner pipe 11 must be
situated
within the upper part 19. The slide joint may thus be transported in two parts
and may
s be installed by first putting lower part 20 together with riser 16,
whereupon the riser is
lowered until the flange coupling 21 is situated at a convenient level. Now
the upper
part 19 may be put together with lower part 20.
In order to keep the internal pipe protected as well as possible during
handling, a
~o lowering procedure has been established for the BOP to be installed
together with the
slide joint, this being that the BOP is held in retracted position and is
locked
hydraulically. This procedure also makes it possible to connect the hydraulic
hoses, as
well as the throttle and shutoff hoses, at a convenient level prior to
installation of the
BOP. All the hoses are collected on the main manifold ring 17. Manifold ring
17 is
is locked in position when the slide joint is slid through the rotary bore. A
special
handling tool is used to install the BOP and to suspend the slide joint. When
the BOP is
locked on the sea bed, the tractive force on the slide joint is activated, and
the inner pipe
11 is drawn out and the suspension head is mounted the suspension socket and
locked
securely there.
