Note: Descriptions are shown in the official language in which they were submitted.
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DRUM UNIT WITH AN ARCH COMPENSATOR FOR A WELL INTERVENTION
STRING
Introduction
The present invention relates to a cable drum with an arch
compensator for an intervention string. More specifically the
invention comprises a device for relative motion between a cable and
a cable drum within a frame in order to keep a constant or very low
fleet angle for the winding or unwinding string. In one embodiment
the drum is arranged to move axially within the frame. In another
embodiment the cable is moved laterally relative to the drum.
Background art and problems related thereto
In well intervention operations using a string spooled externally
onto drum while using an intervention string laying guide imposing a
fleet angle is used. The laying guide shifts the intervention string
laterally and imposes a fleet angle on the string. A fleet angle
variation with otherwise constant drum rotation speed and string
speed usually incurs a tension variation which is undesired. Several
of the published patents comprise a drum with a pivotable rotational
axis so as for maintaining the cable near the perpendicular line to
the drum.
US3524606 Cable reel mounting, describes a drum for lowering and
hauling a cable through a set of horizontal guide rollers on top of
a vertical pipe. The drum axis is arranged pivotable so as for
allowing the cable to run tangentially between the drum and the
rollers for all lateral positions of the cable on the drum, so as
for reducing fleet angle variation of the cable relative to the
drum.
US3690409 describes another pivotable drum arranged for keeping the
fleet angle close to the perpendicular line of the drum by shifting
the ends of the drum axially while the cable is wound or unwound. An
advantage of US3690409 is an increased allowable axial length of the
drum and thus an increased cable length capacity.
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GB2296001 describes a winch apparatus for deploying or taking in
line over a pulley arranged at a distance from the drum. The drum
axis is pivotable so as for maintaining the fleet angle of the line
near the perpendicular.
W02006/027553 Richards describes a drum wherein the incoming line
runs via a diamond screw controlled line guide which lays the cable
with a fleet angle nearly perpendicularly on the drum. The diamond
screw controlled line guide allows for the line to be directed
parallel with the drum axis.
DE19942608 Becker describes a winch with an axially translating wire
drum with a single ply. The axial translation for the wire drum is
for guiding the wire in through a fixed entry position of the winch,
while the drum is alternating along its axis.
W02010/117162 also describes such an axially translating drum in a
frame with a fixed entry point.
US7753344 to Moretz also describes an axially translating drum in a
winch housing with a centrally arranged fixed entry position on the
housing.
US2810439 McCullough describes a wellhead winch with an axially
translating drum in a winch housing, wherein the winch housing is
arranged for being connected under pressure to the wellhead.
EP0571207 describes a winch assembly with a translating drum and a
fairlead for guiding the wire onto the drum under a desired fleet
angle.
Another problem in the prior art is related to relative speed
variations between the drum and the injector head. If we try and
stop an intervention string during a hauling operation running the
string out of the well, we run the risk of damaging the cable or the
injector head very quickly. This is due to the inertia of the
different components involved, because the injector head motors move
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less mass and are much faster to respond than the spooling unit
motor which rotates a drum of considerable rotational inertia.
Conversely, while feeding the intervention string into the well and
suddenly stop it, the rotational inertia of the large drum with its
coiled-up string means that it will continue to try and give out
cable despite the injector head has already stopped the cable. The
usual way of compensating for such speed differences often used in
coiled tubing rig ups is to let the coiled tubing travelling through
the air, so when it is stopped or started quickly the length of the
free air arch changes to compensate. However a free travel of the
intervention string hanging in an arch between the injector head's
gooseneck and the spooling unit may not be desirable both from
safety considerations both to operators or mechanical damage,
particularly when the distance is large and swinging movements of
the string may be considerable.
If an internal laying drum is used, and the injection head is
running the cable into the well and suddenly stops, the inertia of
the large drum means that it will continue to try and give out the
rigid cable even though the injector head has already stopped. This
may damage the cable through longitudinal compression with
subsequent buckling or dislocation.
Brief summary of the invention
The above problems may be remedied through use of the present
invention. The invention is a drum unit for an intervention
string for a well, comprising:
- a drum for said intervention string with a drum axis
and with a radius, arranged in a structural frame and
rotatable by a motor;
- a tension compensator for said intervention string,
- wherein said tension compensator comprises a guide arch
displaceable in a direction generally along the intervention string,
orthogonal to said drum axis, using a first force device
connected to said structural frame for keeping said
intervention string in tension;
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- wherein at least a first end of said guide arch is
laterally displaceable in a direction generally orthogonal to said
intervention string, parallel with said drum axis,
- wherein said intervention string runs between said guide arch
to or from said first end to said drum;
- wherein said intervention string runs via a second, opposite
end of said guide arch via a second, fixed guide at
said structural frame, directly or indirectly to or from said
well.
Further features of the invention are given in the dependent claims
attached.
Brief figure captions
The invention is illustrated in the attached drawings, wherein
Fig. 1 is an isometric view of a drum unit (T) according to the
invention, with an intervention string partly wound up onto the
drum. The intervention string is for a well. The drum is driven by a
motor. The drum unit is provided with a compensator for keeping a
desired tension level in the intervention string (3) during the
running of the drum. Further, the compensator arm is arranged
laterally displaceable driven by an actuator, in a direction
perpendicularly to the string for laying the string in a controlled
way onto the drum. The entire drum apparatus is arranged in a steel
frame. The intervention string may be a carbon fibre reinforced
relatively stiff cable, or an ordinary intervention string or coiled
tubing, is shown running out (or in) to the drum unit.
Fig. IB is a top view of the same embodiment of the invention shown
in Fig. 1B.
Fig. 2 is a side elevation view of a similar embodiment of the drum
unit of the invention, with the frame (2) with the drum in the left
frame part 2A , and the compensator shown in the right frame portion
23. The two frame portions may in an embodiment be split for being
transported separately. A difference between this embodiment and the
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embodiment of Fig. 1 is the position of attachment of the
compensator tension mechanism (6).
Fig. 3 is a side elevation view of the frame, the drum and the
compensator according to the invention, with a generally closed
guideway comprising bending restrictors laid horizontally and over a
gooseneck to an injector head on a well.
Fig. 4 shows end views with two different layup patterns on a drum
according to the invention.
Fig. 5 shows a top view of a drum unit according to the invention,
and a perspective view, an end view as seen from the compensator
arch's end, and a side view, all with the compensator arch in a
retracted position closest to the drum, and with the compensator
arch displaced to one side of the drum.
Fig. 6 shows the same as Fig. 5 except for the compensator arch
being retracted to an extended position relative to the drum.
Fig. 7 shows a separate frame section (2B) with the compensator
arch, as seen from the main drum frame section (2A) position.
Embodiments of the invention
The invention is illustrated in Fig. 1 and Fig. 2, a drum unit (T)
for an intervention string for a well, in particular a petroleum
well. The drum unit comprises the following main features:
- A drum (1) with a radius (R) for the intervention string (0), the
drum (1) arranged in a structural frame (2) and rotatable by a motor
(22). The drum (1) has a radius (R) equal to or larger than a
smallest allowable bending radius (RO) for the intervention string.
For carbon fibre reinforced intervention rods of radii 08 mm to 015
mm used by the applicant, the smallest allowable bending radius (RO)
may be between 0.5 m and 2 m. The diameter of the drum should thus
be >= 2R0, between 1 m and 4 m. The drum (1) should be accommodated
to the largest of these and have a diameter of 4.0 m so the typical
height of the frame would be larger than the drum, e.g. 4.2 m. Such
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a drum may accommodate a cable length of 10 kilometres for a 010 nun
cable. Cables such as composite fibre reinforced cables or other
wireline cables intended for use on the drum may have diameters
varying from 8 mm to 15 mm. A long synthetic fibre cable may thus be
injected by means of a drum unit and a wellhead injector into a
wellhead and extended to near the end of a laterally deviated well.
The drum unit is provided with a tension compensator arch of which a
first end is laterally displaceable in the direction of the drum.
Thus we achieve controlled winding relative of the intervention
string (0) in that the intervention string may run in a controlled
line relative to the drum (1) in the structural frame (2) during the
laying of the intervention string (0) onto the drum (1). The
intervention string is thus shifted laterally to the left and right
onto the drum during receiving or feeding out the intervention
string. A lateral angle on the intervention string, which is almost
generally avoided with the present invention, is called a fleet
angle. A fleet angle variation with otherwise constant drum rotation
speed and string speed usually incurs a tension variation, and the
absence of a fleet angle away from the perpendicular line, and its
cable tension variation is taken up by the compensator arch moving a
small length in and out with the varying entry point onto the drum.
Such tension variations would otherwise have required that the
intervention string had to be operated at a lower maximal tension
onto the drum than by the present invention. The alternative of
running the drum at a speed varying with the fleet angle is
prohibitive if the drum is large.
Fig. 5 illustrates the compensator arch in a retracted position
closest to the drum, and with the compensator arch displaced to one
side of the drum. The fleet angles between the string and the
compensator arm is below 1.6 degrees and the arm is laid over 8
degrees or less laterally.
Fig. 6 shows the same as Fig. 5 except for the compensator arch
being retracted to an extended position relative to the drum. The
fleet angle out of the compensator arch's top is 1.5 degrees or
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less, and the compensator arch is 8 degrees or less inclined
laterally.
The width (aial length) of the drum (1) should be less than or equal
to 1/1 of the internal width of the frame. In the present invention
an embodiment has a drum width of about 1/3 as illustrated, i.e.
0.84 in. The maximal width of the drum is the entire width of the
frame; e.g. about 2.5 m. Such a widening of the drum would incur
significantly larger maximal lateral deviation angles for the
compensator arch, and somewhat increased fleet angles out of the
compensator arch for the increased lateral extension, particularly
in the retracted position.
The tension compensator (3) is for keeping a desired tension in the
intervention string (0) during the running of the intervention
string onto and out of the drum (1). The compensator tightens the
intervention string or yields when speed variations between the
injector head's feeding speed and the speed of the drum occur. The
tension compensator (3) also yields when it moves away from the
central plane of the drum in order to compensate for tension
variations which could be compared to an otherwise varying fleet
angle.
The drum shall operate as a slave subordinate to the injector head.
The tension compensator (3) comprises a guide arch (31) for guiding
the intervention string (0). The radius (Rg) for the intervention
string (0)'s path along the guide arch (31) is larger or equal to
the least allowable bending radius (RO) for the intervention string
(0). In an embodiment the radius may be the same for the guide arch
and for the drum. The guide arch (31) is displaceable to and from
the drum, i.e. in a direction orthogonal to said drum axis (10), by
means of a "force device" (6) attached to the structural frame (2),
i.e. a spring or an actuator or a combination of the two. Other
varieties of a force device may be used. In an embodiment of the
invention the neutral plane of the guide arch (31) is a central
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vertical plane through the frame (2) and the drum as seen in Fig.
1B, wherein the guide arch (31) is deviated to one side of the drum.
- The intervention string (0) runs between a first end (31A) of the
guide arch (31) and a tangential point on the drum (1), please see
the upper part of the guide arch in Fig. 1 or 2. The tension
compensator (3) comprises a guide arch (31) displaceable in a
direction generally along the intervention string (0), orthogonal to
said drum axis (10), using a first force device (6, 6B, 628)
connected to said structural frame (2) for keeping said intervention
string (0) in tension. A first guide (4) may be arranged moving in
synchrone with the lateral movement of the guide arch. The first
guide (4) may be arranged on said first end (31A) of the guide arch
(31) or actuator-driven laterally on the frame.
- The intervention string (0) runs via a second, opposite end (318)
of the guide arch (31) via a second, fixed guide (5) at the
structural frame (1), please see the lower left part of the frame in
Fig. 1, indirectly to the well.
In an embodiment of the invention the drum unit according to the
invention, the guide arch is provided with a second force device
(37), please see Fig. 1, Fig. 5 and Fig. 6, for moving said first
end (31A) laterally so as for steering said intervention string onto
said drum (1).
In an embodiment of the invention, the drum unit according to the
invention, the base of said drum (1) is provided with a groove (11)
so as for guiding the base layer of the intervention string into a
desired pattern on the drum. The inventors have during prototype
experiments discovered that with such a groove (11) in the base of
the drum, this feature may make the second force device redundant,
as the incoming intervention string is steered onto the drum by the
groove when winding up the base layer onto the drum, and then steers
itself laterally for the subsequent string layers onto the drum, and
all the time moves the guide arch's first end (31A) along with it
with a very small fleet angle. The drum may in this embodiment be
provided with a Lebus helical groove along the base so as for
steering the first layer of the cable into an even pattern. The next
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layer on the drum will lay itself neatly onto the base layer, and so
on. In this embodiment the inventors have discovered that the
compensator arm does not have to be provided with the lateral
displacement actuator (37), but winds up nicely with the
intervention string turns wound side by side. However, this
embodiment may readily be combined with the embodiment above for
assuring that the intervention string will go into a desired laying
pattern, such as a dense laying pattern with the string always laid
side-by-side for the densest layering, or in other desired patterns
such as shown in Figs. 4.
In an embodiment of the invention the curve radius of said guide
arch (31) is smaller near its lower second end (31B) and increases
towards it upper, first end (31A). This has been tried on the
prototype and reduces the string tension slightly when hauling in on
the drum, which is advantageous for reducing the laying tension.
Advantages
The fleet angle onto the drum will be negligible when the first, top
end (31A) of the guide arch (31) guides the laying onto the drum (1)
the intervention string (0). The guide arch will, given the
dimensions of the drum, arch and frame shown in Fig. 5A be pivoted
laterally up to 8 degrees left or right for the laying to reach the
flanges of the drum. This will slightly twist the intervention
string (0), minimally, and the twist may easily be taken up anywhere
between the lower end (31B) of the guide arch (31) and the second,
fixed guide (5) which is the entry point for the intervention string
(0) on the fixed frame (2). Additionally, a wider drum may be used
than the 1/3 or 1/2 width drum illustrated: A full width drum may be
used.
Bending of the cable is very small, and more importantly one avoids
the variations in tension with varying fleet angle because the
"curved fleet angle" provided with the laterally moving compensator
arm is, as its name indicates, compensated by in-line variation of
the position of the compensator arm. The lateral force required to
steer the cable into its desired position of the drum is negligible
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and facilitates the laying of the cable to an appropriate position
to facilitate the correct desired spooling pattern of the string
member.
In a preferred embodiment of the invention the drum is an external
laying drum, as shown in the drawings. The laying pattern may be
plain, side by side without any crossings as illustrated in Fig. 1
for fully utilizing the capacity of the drum, or laid in a braided
pattern with one or more crossings per revolution if another pattern
is desired, as illustrated by two examples in Fig. 4.
In an embodiment of the invention the guide arch (31) is arranged
linearly displaceable, i.e. it translates to and from the drum. In
another embodiment it is displaceable by being pivoted about a
first, upper, or second, lower axis (32, 33) arranged in the frame
(1).
In an embodiment of the invention guide arch (32) may be constituted
by a rotating sheave wheel that can translate back and forth, and be
pivotable about the axis of the incoming cable. However, a
significant advantage of using an approximately 180 degrees arch
(32) as shown in Fig. 1 and Fig. 2 is the considerably reduced space
requirement compared to a full sheave.
The force device (6) may in an embodiment of the invention comprise
a spring mechanism (61). The force device (6) may alternatively or
in addition to a spring mechanism comprise a pneumatic, hydraulic or
electrical actuator (62). In Fig. 1 and Fig. 2 a hydraulic piston
embodiment is shown.
The drum (1) is according to an embodiment arranged in bearings on
an auxiliary frame (21). The auxiliary frame may, if it is narrower
than the frame, be mouunted on transverse rails (25) arranged in the
lower structure of the structural frame (1).
The drum unit according to the invention is in an embodiment
provided with one or more string tension feeder units (41, 41A, 41B)
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arranged either on the compensator arm or on the structural frame
(2). The string tension feeder units exert at least a minimally
required tension on the intervention string (0) outwardly directed
from said drum (1) and are arranged for feeding the intervention
string (0) in a desired direction outwardly from or inwardly to said
drum (1). The tension feeder unit (41) shall preferably be employed
during rigging and connection to the injector head (8). When the
injector head on the well has received the intervention string (0)
the tension feeder units may be set in freewheel mode or
disconnected. However, the tension feeder units may be operated
during feeding out the rather stiff intervention string from the
drum in order to prevent the string from raising off the drum. Speed
differences between the drum and the string would be taken up by the
compensator guide arch of the invention anyway.
In an embodiment of the invention, the drum unit (T) is provided
with a tension feeder unit (41A) arranged at a first guide (4) for
said string, said tension feeder unit (41A) arranged laterally
moving with said first end (31A) of said guide arch (31).
In an embodiment of the invention said tension feeder unit (41A) is
arranged at said first guide (4) arranged on said first end (31A) of
said tension compensator (3).
In an embodiment, the tension feeder unit (41A) at said first guide
(4) is arranged laterally displaceable on said structural frame (2),
said tension feeder unit (41A) arranged laterally moving in lateral
synchronous operation with said first end (31A) of said guide arch
(31). In an embodiment the syncrhonous operation may be governed by
means of an actuator (41C).
Said tension feeder unit (41A, 41B) may comprise two or more
motorised rollers or belts (42) oppositely arranged on either sides
of said intervention string's (0) path and arranged for gripping and
exerting a longitudinally directed force on said intervention string
(0).
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According to an embodiment of the invention a tension feeder unit
(41B) is arranged by the second, fixed guide (5), please see Fig. 1.
This will allow the end of the intervention string, or a whip
attached to the end of the string, to be held at this point of the
frame structure when the intervention string is hauled in all the
way to the frame (2). This tension feeder unit (41B) may operate
alone and may hold an outer end or "whip" of the intervention string
(0) by said frame (2) when the intervention string (0) is entirely
coiled in onto the drum. Then, however, with the string laid over
the compensator arch, the structural frame (2) may not be split into
two parts, a drum frame (2A) and a compensator frame (28) because
the whip or outer end of the intervention string (0) still is laid
around the guide arch (31) and locks it in place.
Fig. 7 shows a separate frame section (28) with the compensator
arch, as seen from the main drum frame section (2A) position. The
cabinets shown in the right and left lower portions may provide
space for control units, hydraulic brake or motor units, and
hydraulic units for the compensator arm. The placement near the
lower fixed point of the arm gives ample space for the lateral
movement of the compensator arch.
However, if the whip or outer end of the intervention string is
allowed to be pulled further in onto the drum and locked in a first
tension feeder unit (41A), and this is arranged at the drum frame
(2A), further in relative to the guide arch (31), the guide arch
(31) and the compensator frame (2B) are free may and may be
disconnected, please see below. Then the structural frame (2) may be
disassembled into a drum frame (2A) and a compensator frame (28) and
allow them to be transported as two separate parts.
In an embodiment of the invention the first tension feeder unit
(41A) is arranged at said first guide (4).
The tension feeder unit (41A, 4113) may in an embodiment comprise two
motorised rollers or belts (42) oppositely arranged on either sides
of said intervention string's (0) path and arranged for gripping and
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exerting a longitudinally directed force on said intervention
string, please se the insert detail in the upper left portion of
Fig. 1.
Braking using the motorised rollers or belts will generate heat
irrespective of the motorised rollers use hydraulic or electric
energy. As the brakes are small and there is a risk that they must
brake for extensive lengths, large amounts of heat may be generated.
The heat generated by the braking may be taken out in a hydraulic
brake resistor (43) which may dissipate the heat away from the brake
itself.
In an embodiment of the invention, an intervention string guide
channel (7) of fixed length may be arranged between the second fixed
guide (5) and an injector head (8) on said well, please see Fig. 3.
The guide channel may comprise at least two bend restrictors (71)
for the intervention string (0). The guide channel (7) including the
bend restrictors (71) is preferably closed due to safety
considerations. This has clear advantages; personnel and cranes
cannot interfere directly with any running intervention string. The
guide channel (7) may advantageously comprise pipes of fixed shape
in combination with bend restrictors. In this manner the drum unit
may be placed far from the injector head and the guide channel may
be laid along deck and guided along inclined paths through fixed
pipe sections without requiring much space along its path. The guide
channel (7) may advantageously be lined with a Teflon pipe in order
to reduce friction and wear.
As an alternative to the use of the drum unit being placed separate
from the wellhead injector as shown in Fig. 3, in an embodiment of
the invention the drum unit may be connected directly on the well so
as for the intervention string to run directly from said fixed guide
(5) of the structural frame (2) to the injector head (8), i.e. that
the structural frame (2) to be arranged directly above the injector
head (8).
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The intervention string (0) is a relatively rigid fibre reinforced
cable (01), generally of a slick carbon fibre type, or a coiled
tubing (02) or an otherwise slick metal string (03). The
intervention string may comprise an electrical conductor, a fluid
communication line, a signal fibre, or combinations of two or all of
those.
The drum unit illustrated in Fig. 1 has a typical length of 7.14 m,
a height of 4.20 m, and a width of 2.49 m. The total length of the
unit may prove impractical for transport. In an embodiment the drum
unit's structural frame (2) is assembled from a drum frame (2A) and
a compensator frame (28) which may be disconnected and reassembled.
The guide arch (32) is in an embodiment of the invention provided
with a series of small sheaves (34) along its radially outward
facing arch length for supporting and guiding the intervention
string (0). The sheaves guide the intervention string and reduces
friction between the string and the guide arch. As the string runs
externally along the arch on the sheaves the arch must keep the
intervention string in a tension sufficient for the string to bend
into the bending radius of the intervention arch. This is obtained
using the force device (6) to take up any slack of the string.
Additionally, the tension of the string may be controlled using the
first and second guides' (4, 5) tensioner rollers.
As mentioned above, the compensator must tighten or yield the
intervention string when speed variations between the injector
head's feeding speed and the speed of the drum occur. Further, the
drum shall operate as a slave subordinate to the injector head.
To achieve this, the drum unit is in an embodiment provided with a
control system (CS) arranged for receiving control signals from a
higher order control system for the injector head (8) on the
wellhead. The higher order control system sends commands for feeding
down, halting, or hauling up the intervention string. Further, the
control system sets the speed required for the intervention string
(0) accordingly. The control system is arranged for coordinating the
movements of the intervention string on the drum (1) with the
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movement of the intervention string running through the injector
head (8). As the two have different inertia, differences during
injection and hauling are taken up by using the compensator. After
having compensated for a reduced tension in the string due to high
rotational inertia of the drum and coiled-up string when the
injector head suddenly reduces its speed, the compensator arch is
run outwardly relative to the drum axis. If, conversely, the
injector head increases its injection speed, the compensator arch
may be allowed to run inwardly in order for allowing the drum to
catch up, and subsequently the compensator arch is returned to near
a neutral middle position in order for meeting a subsequent need for
slacking or tensioning the string.
The above described embodiments may all be combined except when
mutually exclusive. An example of mutually exclusive combinations is
the fact that a rigid guide arch (31) cannot be arranged pivotable
about both the upper and the lower axis (32, 33) at the same time,
because the guide arch then would be locked in place.
As mentioned under the initial presentation of problems related to
prior art, problems caused by relative speed variations between the
drum and the injector head may be remedied using a free hanging
cable between the gooseneck and the drum. However, the inertia
problems become more apparent if a string channel of fixed length
outside the wellhead, e.g. with a series of bend restrictors is
used, because this creates a fixed distance between the spooling
unit and injector head, and this requires compensation for speed
variations. In such situations the tension compensator of the
invention becomes a significant advantage.
The present invention has been indicated as a drum unit (T) for an
intervention string (0) for a well. First and foremost a petroleum
well is the intended area of use, but a geothermal well or a water
well is also possible.
