Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Locking mechanism
The invention relates to well operations, especially in connection with
production of
hydrocarbons from underground formations. More specifically, the invention
relates
to a device for heave compensation of equipment on a moving vessel, as
disclosed
in the preamble of the independent claims.
Background of the invention
During the recovery of hydrocarbons from wells in underground formations, the
operator must sometimes carry out work in the wells. Such work may be
maintenance or other technical operations, such as perforating, replacing or
reperforating pipes, changing flow regulators, isolating production zones,
monitoring production and logging pressure, flow and temperature. A motivating
factor for the work is to increase the recovery rate of the well. This work,
which is
referred to by the collective term 'well intervention', is difficult to
perform from
conventional surface platforms, especially wherusubsea wells are involved. It
is
well known that subsea wells are less maintained than platform wells and hence
have lower recovery rates. It is therefore desirable to have systems that are
suitable
for maintenance of subsea wells.
A distinction is made between light well intervention and heavy well
intervention.
Today, light well intervention is carried out with the aid of wireline
operations from
a ship. Heavy well intervention (which includes the whole spectrum of
intervention
work) is usually carried out from a special moored, semi-submersible rig that
is
connected to the wells via a riser (pipe for gas and/or liquid). The special
rig fills
the gap between the ordinary drilling rigs and the vessels that carry out
light well
intervention using wireline operations, and has, inter alia, substantially
lower costs
than an ordinary drilling rig.
To further optimise costs, it is therefore desirable that such special rigs
are of
maximum flexibility, such that, for example, in addition to carrying out heavy
well
intervention they can also carry out light well intervention using wireline-
operated
tools.
Known floating intervention rigs have a drilling machine suspended from a
tower
via a heave compensation system for compensating for wave motions, which may
comprise a combined hoisting and compensation cylinder. The tower and the
cylinder are mounted on deck. In an ordinary device, the drilling machine is
suspended from wires (so-called drill line), which run over guide pulleys at
the top
of the mast, via reversing pulleys at the top of the cylinder, :to a fixed
point at the
top of the mast. The drilling machine can therefore be hoisted up and down by
moving the cylinder, and the cylinder also compensates ¨ within certain
tolerances ¨
for the motions of the rig such that the drilling machine is kept as steady as
possible
when carrying out intervention operations. A combined hoisting and
compensation
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cylinder of this kind is capable of handling large loads, typically in the
order of 250
tonnes.
This device is used, for example, when landing large weights on the seabed or
inside the drilling riser, as well as during drilling, and can be operated in
passive or
active compensation mode when there is a need for greater accuracy and control
of
the compensation.
The prior art comprises WO 2007/145503 Al, which describes a device and a
method for heave compensation. A mast is mounted on a floating vessel, a first
compensation means that is attached via wire means on one side of the mast,
and the
other end of the wire means is further connected to a second heave
compensation
means attached to a tool unit for carrying out drilling operations. The second
heave
compensation means and the tool unit are moved along guide rails in the mast
with
the aid of dollies/lever arms.
There are stringent requirements as regards the ability.ottne well
intervention rig to
¨ very accurately ¨ compensate for the movements of the rig. Heave
compensation
requirements are often concretised as an ability to compensate weight change,
positioning accuracy and speed limitation. In known well intervention rigs,
however, the size of the combined hoisting and compensation cylinder, and the
friction in the guide pulleys and reversing pulleys make it difficult to
satisfy one or
more of these requirements. There is therefore a need for a device that is
capable of
obtaining greater accuracy in heave compensation than is the case with known
well
intervention rigs. The invention meets this need and has other advantages in
addition.
Summary of the invention
Therefore, a device is provided for heave compensation of a tool unit which is
suspended via one or more wire means in a mast mounted on a platform, each
wire
means at a first end being attached to the mast via an attachment and running
via a
first heave compensation unit, and each wire means at its other end being
attached
to a second heave compensation unit that is connected to the tool unit,
characterised
in that the second heave compensation unit comprises a movable compensation
means which at its first end is attached to the wire means and which at its
second
end is attached to the tool unit, and that the second heave compensation unit
comprises a releasable locking means with which the motions of the
compensation
means can selectively be prevented and allowed.
In an embodiment, the compensation means is attached to the wire means via a
connecting unit and is attached to the tool unit via a link element, the
connecting
unit and the link element being movable in relation to one another, and where
the
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locking means is movable for selectively and releasably limiting the motions
of the
connecting unit and the link element in relation to one another.
In an embodiment, the locking means comprises a locking bolt with a central,
narrowed portion and broad shoulder portions at each end of the bolt.
In an embodiment, the link element comprises a through hole having a first
portion
and a second portion, the first portion having a larger opening than the
second
portion. The first portion has a dimension that allows passage of the shoulder
portions whilst the second portion has a dimension that does not allow passage
of
the shoulder portions, but does allow passage of the central portion. In an
embodiment, the first portion has a circular cross-section and the second
portion is
elongate.
In an embodiment, the wire means runs between the second heave compensation
unit and the first heave compensation unit via guide pulleys that are mounted
at an
upper part of the mast, and run via the first heave compensation unit between
the
guide pulleys and the attachment in the mast.
In an embodiment, the first heave compensation unit is connected at a first
end to
the platform and at a second end is movably attached to said wire means via
reversing pulleys and a cylinder.
In an embodiment, the device comprises locking means with which the movements
of the compensation units can selectively be prevented, and the compensation
units
transfer loads between the tool unit and the wire unit as substantially rigid
bodies.
In an embodiment, the first heave compensation unit functions as an active
heave
compensator whilst the second heave compensation unit functions as a passive
heave compensator.
In an embodiment, the second heave compensation unit is an integral part of
the tool
unit. The first and second heave compensation units are preferably
hydraulically
operated.
The second heave compensation unit can quickly and simply be installed on any
drilling machine, without structural modifications of the drilling machine.
Overview of the figures
These and other characteristic features of the invention will be elucidated in
the
following description of preferred, non-limiting embodiments, with reference
to the
accompanying schematic drawings, wherein:
Figure 1 shows a mast with a compensation system, seen from a side;
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Figure 2 shows a mast with the compensation means according to the
invention, seen from the front;
Figure 3 shows the mast and the compensation means shown in Figure 2, but
from another side;
Figure 4a shows a section of a first embodiment of the invention, seen from a
side, where the cylinders in the second heave compensation unit are in a
retracted
position;
Figure 4b shows the section shown in Figure 4a, seen from the front;
Figure 4c corresponds to Figure 4b, but shows the cylinders in the second
heave compensation unit in a fully extended position;
Figure 4d corresponds to Figure 4b, but shows the cylinders in the second
heave compensation unit in a mid position;
Figure 5a shows a section of a second embodiment of the invention, seen
from a side, where the cylinder in the second heave compensation unit is in a
retracted position;
Figure 5b shows the section shown in Figure 5a, seen from the front;
Figure 5c corresponds to Figure 5b, but shows the cylinders in the second
heave compensation unit in a fully extended position;
Figure 5d corresponds to Figure 5b, but shows the cylinders in the second
heave compensation unit in a mid position;
Figure 6a shows a section of a third embodiment of the invention, seen from
a side, where the cylinder in the second heave compensation unit is in a
retracted
position;
Figure 6b shows the section shown in Figure 6a, seen from the front;
Figures 7a and 7b show the third embodiment of the heave compensation
unit in an unlocked state, seen respectively from the front and from a side;
Figures 7c and 7d are an enlarged section of Figures 7a and 7b respectively,
and Figure 7e is a sectional view of that shown in Figure 7d;
Figures 8a and 8b shows a locked state, where the motion damper has not
been activated;
Figures 8c and 8d are enlarged sections of Figures 8a and 8b respectively,
and Figure 8e is a sectional view of that shown in Figure 8d;
Figures 9a and 9b show a state in which it is possible to pull the locking
bolt
out of the keyhole, and Figure 9c is an enlarged sectional view of that shown
in
Figure 9b; and
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Figures 10a and 10b shows a position for weight reduction by screwing
together drilling machine and drill string, a so-called "thread-saver"
function, and
Figure 10c is an enlarged sectional view of that shown in Figure 10b.
Description of preferred embodiments
Figure 1 shows a mast 1 located on a deck 2, for example, on an intervention
rig or
drilling rig (not shown). An active heave compensation cylinder 7 and
accumulator
8 and a combined hoisting and heave compensation cylinder 4 are mounted on the
deck 2. The heave compensation cylinder 4 is equipped at its upper end with
reversing pulleys 5 for hoisting wires 6. It is usual to have four or six
parallel
running hoisting wires.
With reference to Figure 2, the combined hoisting and heave compensation
cylinder
4 has a length of stroke d, where the cylinder rod 12 is in a fully extended
position.
The fully retracted and extended positions, respectively, of the reversing
pulleys are
indicated by the reference numerals 5 and 5'.
In the illustrated embodiments, the mast is constructed of a lattice structure
in a
known way, and will therefore not be described in more detail here. Similarly,
the
heave compensation units are driven by fluid reservoirs, regulating valves and
systems, gas tanks and hydraulic power units. These components are well known
to
the skilled person and are therefore not referred to in more detail here.
The mast is equipped with guide rails 9 for a drilling machine 11 in a known
way.
Furthermore, with reference to Figures 2 and 3, the wires 6 are connected to
the
upper part of the mast via an anchorage 10. The wires 6 run from the anchorage
10
via the reversing pulleys 5 on the cylinder rod 12 of the combined hoisting
and
heave compensation cylinder 4, onward via guide pulleys 3 at the top of the
mast
and then down to a compensator 20, which is connected to the drilling machine
11.
Figure 2 shows the combined drilling machine 11 and compensator 20 in a lower
position against the deck 2, whilst these units in Figure 3 are raised
slightly from
the deck.
Three embodiments of the compensator are described below.
First embodiment:
Referring to Figures 4a-d, the compensator 20 comprises two cylinders 22a,b
that
are directly connected between the drilling machine 11 and the connecting link
24
of the hoisting wires. The hoisting wires (not shown in Figures 4a-c) are
connected
to the connecting link 24 via suitable attachments 25. Figure 4a further shows
a
dolly 21 attached to the drilling machine 11 for engagement with the tower
guide
rail as described above.
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The cylinders 22a,b are equipped with a lock 23 with which the cylinders can
be
locked in the retracted position when the system is not in use. The load from
the
drilling machine 11 is transferred to the lifting wires via the cylinders
22a,b and the
connecting link 24.
Figures 4 a,b show the cylinders 22a,b in a retracted position, Figure 4c
shows the
cylinders 22a,b in a fully extended position, whilst Figure 4d shows the
cylinders
22a,b in a mid position. The reference numeral 26 indicates the respective
cylinder
rods of the cylinders.
Fluid reservoirs and control units for the heave compensation cylinders 22a,b
are in
accordance with the prior art and are therefore not discussed in more detail
here.
Second embodiment:
Referring to Figures 5a-d, the compensator 20' comprises one cylinder 27 which
is
connected between the drilling machine 11 (via a link 29) and a connecting
link 28
for the hoisting wires (only attachments 25 for the wires are shown in Figures
5b-d).
Figure 5a further shows a dolly 21 attached to the drilling machine 11, for
engagement with the tower guide rail as described above.
The cylinder 27 is equipped with lock 23 with which the cylinders can be
locked in
collapsed position when the compensator 20' is not in use. The load from the
drilling machine 11 is transferred to the hoisting wires via the cylinder 27
and the
connecting link 28.
The figures 5a,b show the cylinder 27 in a retracted position, Figure Sc shows
the
cylinder 27 in a fully extended position, whilst Figure 5d shows the cylinder
27 in a
mid position. The reference numeral 26 indicates the cylinder rod of the
cylinder.
Fluid reservoirs and control units for the heave compensation cylinder 27 are
in
accordance with the prior art and are therefore not discussed in more detail
here.
Third embodiment:
With reference to Figures 6a to 10c, the compensator 20" comprises one
compensator cylinder 31 (also referred to as a motion damper) that is mounted
to a
connecting piece 32 for the hoisting wires. Figures 6a and 6b further show a
dolly
21 attached to the drilling machine 11, for engagement with the tower guide
rail as
described above. On the connecting piece 32 there is mounted a lock 30 (which,
for
example, is hydraulically operated via an actuator 86) that is capable of
connecting
together the connecting piece 32 and the below-lying link element 33 from
which
the drilling machine 11 is suspended. The lock 30 bears all load when it is in
the
locked position and the compensator 20" is not in use, such that the load from
the
drilling machine 11 is transferred to the hoisting wires via the link element
33, the
hydraulically operated lock 30 and the connecting piece 32. Figures 6a,b show
such
a locked position, in which the cylinder 31 is in a retracted position and is
inactive.
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Fluid reservoirs and control units for the compensation cylinder 31 are in
accordance with the prior art and are therefore not discussed in more detail
here.
Figures 7a to 10c are further illustrations of the compensator cylinder 31,
the
connecting piece 32, the link element 33 and the connection between these
components in different configurations.
The connecting piece 32, to which the compensator cylinder 31 and the wires 6
are
fastened, comprise two plate elements 32a,b arranged spaced apart and fastened
together by means of upper bolts 81 and lower bolts 83. The lock 30, with its
hydraulic actuating mechanism, is also attached to the connecting piece
(hydraulic
connecting lines are not shown, as they are prior art). The lock 30 comprises
a
housing 30' with a locking bolt 87, a locking bolt cylinder 88 and a position
sensor
89 for the locking bolt. The locking bolt 87 has a central narrowed portion
87b, and
broad portions (flanges) 87a at each end.
In this illustrated embodiment, the link element 33 also has a plate form, and
is
disposed between the plate elements 32a,b of the connecting piece in such a
way as
to be movable. The cylinder rod 26 of the compensator cylinder 31 (whose
housing
is fastened to the connecting piece) is secured to the link element 33 via a
fastening
bolt 84. The link element 33 is provided with a through "keyhole" 82, which is
adapted for receiving the locking bolt 87. The keyhole 82 is elongate and has
a
lower portion 82a that has a larger opening than the above-lying, slightly
narrower
portion 82b of the keyhole.
The broad end portions 87a of the locking bolt 87 have a cross-sectional
dimension
that allows passage through the lower, broad portion 82a of the keyhole and
into the
respective support holes 37 in the side plates 32a,b, but does not allow
passage
through the above-lying portion 82b. The central, narrowed portion 87b of the
locking bolt has a cross-sectional dimension that allows movement of the
locking
bolt up and down in the keyhole, also in the slightly narrower portion 82b.
Figures 7a-e show an unlocked state. The locking bolt 87 has been fully
withdrawn
from the keyhole 82 in the link element 33, thereby allowing the link element
33 to
move between the two side plates 32a,b in the connecting piece 32. The link
element 33, which is connected to the compensator cylinder 31 via the cylinder
rod
26, can move between a lower position (as shown) and an upper position,
limited
by, respectively, the upper shoulders 85 and lower shoulders 90 and the lower
(stop)
bolts 83. The figures show that when the link element 33 is in the full lower
position, it will rest on the two lower bolts 83 via the shoulders 85, which
will
prevent the drilling machine from falling if the compensator cylinder 31
should fail.
When the cylinder stroke is reduced to about half stroke (compared with that
shown
in Figures 7a-d), the system will be in the position for motion damping.
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Figures 8a-e show a locked stated wherein the motion damper 31 is not in use.
The
system is locked, such that all load passes through the locking bolt without
affecting
the motion damper. The load is suspended from the drilling machine (not shown)
and is transferred to the link element 33. The link element 33 is suspended
from the
locking bolt 87 that is seated in holes in the side plates 32a,b of the
connecting
piece 32. From the locking bolt 87, the load passes through these two side
plates up
to the upper bolts 81, which connect the hoisting wires to the connecting
piece 32.
This is a normal configuration of the suspension system for drilling and
lifting/lowering the drill string.
Figures 9a-c show a state in which the lower link element 33 has been lifted
up to a
maximum height in the keyhole 82, such that the locking bolt shoulders 87a and
the
broad portion 82a of the keyhole are aligned with one another. This is the
only
position in which it is possible to pull the locking bolt 87 out of the
keyhole 82. The
locking bolt is moved (pulled) horizontally by means of a cylinder 88 equipped
with
a stroke sensor 89 such that there is control of whether the bolt is in
lockable
engagement with the keyhole or not. This lifting of the link element 33 is
done with
the aid of the compensator cylinder 31. As described above, Figures 9a-c also
show
that the lower dimension (diameter) of the keyhole is so great that the
locking bolt
can be moved horizontally through the keyhole. In the upper, narrower part of
the
keyhole, it is not possible to move the locking bolt in a horizontal direction
owing
to the shoulders having increased diameter at the ends. However, the locking
bolt is
free to be moved vertically in the keyhole, throughout the length of the
keyhole.
The sectional view in Figure 9c shows the locking bolt half out of engagement.
It
can be seen that the locking bolt has a shoulder 87a with a larger diameter at
both
ends than the diameter of the central portion 87b. The diameter of the
shoulders fits
in the supporting holes 37 of the connecting piece 32 and the lower part 82a
of the
keyhole in the link element.
Figures I Oa-c shows a state in which the locking bolt 87 is locked, but the
damping
cylinder 31 (not shown in Figures 10a-c) is actuated with a small stroke such
that
the locking bolt is roughly in the middle of the keyhole 82. This is a
position for
weight reduction on screwing together the drilling machine and the drill
string, a so-
called "thread-saver" function.
The task of the compensator 21" is to hold tool that has been lowered into the
well
in an accurate position without subjecting equipment installed in the well to
weights
greater than typically +/- 500 kg whilst the main heave compensation is in
progress
with the aid of the combined hoisting and heave compensation cylinder 4, with
associated accumulator tanks and other necessary, known equipment (not shown).
The compensator 21" with compensation cylinder 31 takes the "peaks" of the
damping from the main compensator 4.
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The compensator 21" may thus have at least the following two functions:
a) Damping/minimising vertical motion and controlling/minimising load
against
components inside the well from tools that may be lowered down into it; and
b) Reducing the load between the shaft of the drilling machine and the top
of the
drill pipe when they are to be screwed together (thread-saver).
Although the compensator 21" is described here as being made up of a lower
link
element 33 that is movably arranged between the two side plates 32a,b of the
connecting
piece 32, the invention should not be limited to such designs, as a variant
may be an
inverted configuration where the lower link element has two side plates and
the
connecting piece comprises one element that is movably arranged therebetween.
The
invention should also not be limited to plate-shaped elements.
Features common to the embodiments:
The combined hoisting and heave compensation cylinder 4 and associated
components
(in the following also referred to as Stage 1) are used when landing large
loads on the
seabed or inside the drilling riser, and during drilling. In such situations,
the compensator
20; 20'; 20" is not necessarily in use, i.e., the cylinders are locked via
their respective
locking mechanisms 23; 30.
For heave compensation, Stage 1 can be operated in passive compensation mode
or in
active compensation mode.
In situations where greater accuracy and control of the compensation are
required, as for
example, during well intervention, Stage 1 will be operated in active
compensation mode.
Stage 1 will therefore be able to achieve heave compensation down to a certain
minimum
level.
The compensator 20; 20'; 20" (in the following also referred to as Stage 2) is
used
together with Stage 1 in order to further increase sensitivity and accuracy,
and to ensure
that the power of the drilling machine does not exceed a defined minimum
value. Stage 2
then functions as a passive heave compensator. The compensator in Stage 2,
which may
have a relatively short stroke length, is constructed such that the cylinder
piston is held
stationary until loaded with a predefined weight. When such a predefined
weight has
been reached, the compensator in Stage 2 will compensate by either retracting
or
extending the cylinder rod 26.
Examples of situations in which the need for a Stage 2 is present include
landing of
lighter equipment within the casing and subsea safety valves.
A two-stage heave compensator of this kind can thus ¨ very accurately ¨
compensate for
the motions of the rig. Within given operational parameters (e.g., max heave
motion of
rig), Stage 1 and Stage 2 in combination can compensate for a relatively small
weight
change and obtain major positioning accuracy at a limited speed. As mentioned
above, a
combined hoisting and compensation cylinder can typically handle loads of the
order of
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250 tonnes. In such a connection, a relatively small weight change may be of
the order of
500 kg, and the positioning accuracy can be of the order of 10 cm.
Stage 1 can handle large loads and most of the heave. The compensator 20; 20';
20"
(Stage 2) is however substantially smaller than Stage 1 and thus generates
less packing
friction. In addition, the compensator in Stage 2 is located on top of the
drilling machine
11 such that it does not take with it other friction than that in the
compensator 20; 20';
20", and possibly some from the well.
The compensator 20; 20'; 20" is thus able to reduce the load amplitude from
Stage 1 to a
load oscillation that is within the requirement for weight change
compensation.
The device according to the invention functions in this way as a two-stage
heave
compensator, where the combined hoisting and heave compensation cylinder 4
(Stage 1)
handles the large loads, whilst the compensator 20; 20'; 20" (Stage 2, which
has better
sensitivity and greater accuracy) is able to compensate for loads that are
smaller than
Stage 1 is adapted to compensate for.
In an embodiment, the load for which the compensator 20; 20'; 20" is designed
to
compensate may be of the order of 8-10% of the load capacity of the hoisting
system.
It will be appreciated that the device for heave compensation can be used for
purposes
other than well intervention.
The numerical values in the description above have been included to illustrate
the
application of the invention, and should not be regarded as a limitation of
the invention.
