The present invention relates generally to a composite tube for use
inserted in or connected to a bore hole in the ground, such as in the exploration
and the winning of oil and gas.
Composite tubing, in particular composite tubing capable of being
spooled upon a reel, is commonly used in numerous well operations, including
running wire line cable down a lithosphere bore hole with well tools, working
over wells by delivering various chemicals down hole and performing
operations on the interior surface of the drill hole. The spoolable composite
tubes can be used in conjunction with one well and can then be transported on
a reel to another well location. The composite materials used comprise
reinforcing fibers, such as carbon, glass or aramid, and a matrix material, such
as a thermoplastic or thermosetting polymer, supporting the fibers.
Compared to steel tubing, composite coiled tubing has increased
corrosion and fatigue resistance, combined with a high strength to weight
A recent development in composite tubing is to embed electric power
conductors within the wall thickness of the composite tube to enable the use of
electrically powered devices suspended on or attached to the tube. In addition,
data transmission is possible by superimposing a data signal on the power
Spoolable composite tubing comprising embedded power conductors as
well as methods for their manufacture and the uses of such tubes in bore holes
are disclosed in US 5 921 285 and WO 99/19653.
A problem associated with composite tubes with embedded power
conductors is to embed a power conductor capable of conducting relatively
large amounts of electrical energy in the tube wall without significantly
compromising dimensions, strength, flexibility or structural integrity of the
In particular, to supply sufficient power to an electric drilling motor, a
submersible pump or an electric tractor, typically three copper electrical
conductors are needed each having a cross sectional area of 35-40 mm2.
Such a conductor must be integrated in the tube wall without
significantly decreasing its inner diameter and/or significantly increasing its
outer diameter. Decreasing the inner diameter leads to a decrease of the area
provided for fluid transport, while an increase in the outer diameter increases
the dimension of a spool on which the tube is coiled, thus leading to
transportation problems. Furthermore, increasing the outer diameter is often
not desirable in view of the limited cross-sectional area of the bore hole.
It is an object of the present invention is to provide a spoolable
composite tube having power conductors embedded in the tube wall capable of
transmitting sufficient power for at least one downhole electric power tool such
as a downhole electric drilling motor, an electric submersible pump or an
electrical tractor, without significantly compromising its dimensions, strength,
flexibility or structural integrity and particularly its ability to be bent to a
small radius without being permanently deformed or damaged otherwise.
This object is achieved by providing a tube according to claim 1.
By configuring the conductor as a strip-like element, the cross-sectional
area of the element in the tube wall can be relatively large. The plurality of
conducting filaments provide the conductor with a structure capable of
accommodating to relatively large temporary deformations of surrounding
material which occur during spooling of the tube to a relatively small radius.
The capability of accommodating to relatively large temporary
deformations of the tube wall is markedly improved if each of the conductive
filaments is at least partially oriented at an angle relative to the strip-like
element of which it is a member. Thus can for instance be accomplished by
The capability of accommodating to deformations of the tube and the
ease of assembling the composite structure of the tube are further enhanced if
the conductive filaments are braided, intertwined or braided and intertwined.
A braided and/or intertwined structure of the strip-like elements also provides
the advantage that the filaments are bundled so that handling of the strip-like
element or elements before integration in the tube wall is facilitated.
The filaments can for instance be interwoven separately, but can also be
interwoven as strands.
The strip-like element may comprise both electrically conductive
filaments and electrically non-conductive filaments. The conductive and the
non-conductive filaments can be interwoven.
The strip-like elements configured as flattened braids embedded in the
tube wall thus provide a relatively large cross-sectional conductive area that
can be arranged in the tube wall with a minimum impact on its dimensions,
strength and wear-resistance. In particular, the easily deformable structure of
the braids provide for low deformation of the conductor filaments in the tube
wall when the tube is bent.
Preferably, the strip-like elements comprise a flattened tubular
structure of crossingly interwoven strands of electrically conductive filaments,
e.g. copper wires.
Although the longitudinally extending strip-like elements can be
arranged in many configurations along at least a part of the tube's length,
such as helically, as a sequence of S-turns or forming a zigzag pattern, the
strip-like elements are preferably oriented substantially parallel to the tube
axis. Thus, the strip-like elements form a balanced composite structure so that
that tensile, flexural and pressure loads exerted thereon do not induce
torsional loads exerted onto the tube.
The concept of the electric power conductor embedded in the tube wall
being formed by a flexible, strip-like element comprising a plurality of
electrically conductive filaments is of particular advantage if at least two of
the power conductors are included in the tube wall and positioned mutually
spaced in circumferential sense of the tube. This because considerations
regarding occupied cross-sectional area and mutual insulation are of particular
importance if a plurality of power conductors is required.
By providing three strip-like elements, the elements having
substantially equal dimensions and being distributed substantially equally
along the circumference of the tube wall, it is achieved that the tube has equal
bending stiffnesses in all directions.
By arranging the strip-like elements to curvedly extend along a part of
the circumference of the tube wall, it is achieved that the elements can be
accommodated in a circumferential layer of the tube wall. Preferably, the
strip-like elements or braids are curved substantially concentrically to the
tube axis. This way, the radial thickness of a layer comprising the braids can
By embedding the strip-like elements in a circumferential layer of
electrically non-conductive composite material it is achieved that the layer
containing the braids can add to the structural strength of the tube. This way,
the impact of the embedded conductors on the structure of the tube can be
Such a non-conductive composite layer can also comprise an axially
extending circumferential layer of electrically non-conductive composite
material covering the strip-like elements on the outside and/or the inside,
while the circumferential area between the strips is filled with a composite or
a non-composite material, e.g. the matrix material of the composite material of
the covering layers. This way, the electrically non-conductive layer with
embedded strips can be manufactured relatively easily, e.g. by means of the
thermoplastic tape winding process. It is also possible to provide that the
electrically non-conductive layer inside of the strips also forms the inner liner.
By impregnating the strip-like elements with non-conductive material,
e.g. with the matrix material also included in the electrically non-conductive
layers, bonding between the surrounding non-conductive, insulating layers can
be increased. Preferably the matrix material is applied by pre-impregnating
before bringing the strip-like elements in the intended position. In addition
voids in the braids can be reduced and mechanical and electrical behaviour can
be improved. By using a thermoplastic material, the conductors can be
manufactured in the same way as composite tapes, which facilitates
manufacturing the tube by means of the thermoplastic tape winding process.
By providing the tube with a pressure resistant, inner tubular liner the
pressure resistance of the tube can be increased. Such a tubular liner can
conveniently be used as a mandrel on which the composite layers are wound.
Preferably, such a tubular liner comprises a non-composite, thermoplastic
Use of thermoplastic material in the tube wall allows local plastic
deformation of the tube wall resulting in cracks being closed or evening out of
other stress or wear-induced damage, in particular under influence of heat
and/or incidental large deformation.
Further advantageous embodiments are discussed in the appended
The invention will be further elucidated using an example shown in a
drawing. In the drawing:
- Fig. 1 is a cross-sectional view of a composite tube;
- Fig. 2 is a perspective view of the tube of Fig. 1;
- Fig. 3 is a perspective, partially cut away view of a connector-coupler
assembly for connecting the tubes end to end;
- Fig. 4 is a longitudinal, cross-sectional view of a detail of the connector
of Fig. 3;
- Fig. 5 is a schematic side view representing an operating sequence in
which a tube as described is employed;
- Fig. 6 is a schematic side view showing use of a tube as described for
retrieving an object from a bore hole; and
- Fig. 7 is a schematic side view showing use of a tube as described as a
riser with integrated power conductors for controlling a subsea unit.
The drawings only serve as non-limiting elucidations of a preferred
embodiment of the invention. In the drawings, identical parts are denoted with
the same reference numerals.
Figs. 1 and 2 show a composite tube 1. The tube comprises a tube wall 2
having a number of circumferential layers axially extending along central axis
A of the tube 1 in a laminar fashion.
The tube wall 2 comprises a central layer 3 of electrically non-conducting
composite material. The non-conducting layer of composite
material comprises a thermoplastic matrix material, e.g. polyetherimide (PEI),
polyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyvinylidene
fluoride (PVDF), polyethersulfone (PES), polysulfone (PSU), polyethylene
terephthalate (PET), polyamideimide (PAI), polyurethane (PUR), polyamide
(PA), polypropylene (PP) or polyimide (PI), reinforced with fiberglass or other
fiber materials. The specific selection of materials will typically be governed by
operating conditions and other application dependent requirements the tube
will have to fulfil.
Embedded in the electrically non-conductive layer are three electric
power conductors, each extending substantially parallel along the tube axis A.
The power conductors are each formed as a flexible strip-like element 4
comprising a plurality of electrically conductive, braided filaments. The strip-like
elements are formed as flat braids wherein strands 5 of copper wires 6 (fig.
1) that axially extend along axis A are arranged in a crossing fashion. The
angle between the axis of the strip and the axes of the conductive elements
therein is preferably between 15° and 70° and preferably between 35° and 55°.
The flat, strip like elements 4 each have substantially equal dimensions
and are distributed substantially equally along the circumference of the tube
wall 2. Depending on the diameter of the tube and the required conductive
cross-sectional area, the thickness to width ratio of the strips is preferably
between about 1:50 and about 1:3 and most preferably between about 1:20 and
Each element 4 is substantially flat and extends curvedly along a part of
the circumference of the tube wall 2, the curvature being substantially
concentrically to the tube axis A.
The electrically non-conductive composite layer 3 wherein the flexible,
strip-like elements are embedded is composed of a radially outwardly and a
radially inwardly disposed covering layer 3A, 3B covering the interposed strip-like
elements 4, which are contained in an intermediate layer 3C. The covering
layers 3A, 3B comprise a thermoplastic matrix material having fiber
reinforcements, while in this example the material of the intermediate layer
3C between the strips is a thermoplastic matrix material without fiber
reinforcement. For ease of application, it can also be advantageous to provide
that the material of the intermediate layer 3C between the strips is a
thermoplastic matrix material including fibers, for instance in the form of
pultruded strips. In the thermoplastic material the flexible, strip-like elements
are embedded. The strip-like elements are impregnated with the thermoplastic
To obtain electromagnetic shielding, the strip-like elements 4 are
radially interposed between axially extending, electrically conductive
composite circumferential layers 7A, 7B with carbon fibre as electrically
conductive high strength material. The layers can be made electrically
conductive by adding conductive particles such as carbon black to the matrix
The tube 2 further comprises a pressure resistant inner tubular liner 8.
The liner 8 is preferably made of a non-composite thermoplastic material, such
as: PEEK, PPS or PVDF, the particular choice being dependent on
requirements for instance regarding operating conditions and chemical
resistance. The inner liner 8 carries the radially outwardly disposed
circumferential layers 7B, 3B, 3C, 3A, 7A as a mandrel.
The tube 1 further comprises an axially extending corrosion resistant
and/or impact resistant, radially outer circumferential shielding layer 9. The
shielding layer is preferably formed by a composite of PPS and wear resistant
material such as glass fibers.
The tube wall 2 according to the present example comprises axially
extending optical fibers, schematically represented by dots 22, disposed in the
electrically non-conductive layer for monitoring partial discharges generated
by a voltage applied on the electrical conductive elements 4. This way,
structural integrity of the insulating layers can be monitored.
Referring to Figs. 3 and 4, the tube ends 10 comprise additionally
reinforced wall portions of increased radial dimension. The reinforced wall
portions are used for attachment of a connector 11. The connector 11 comprises
an inner portion 12 for supporting the inner surface of the tube formed by the
The connector 11 further comprises a cover mantle 13 for covering the
outer surface of the tube which can be placed onto the inner portion 12 such
that the inner portion 12 and the cover mantle 13 clampingly engage end wall
portion 10 of the tube 1. Preferably, the inner portion 12 and the cover mantle
13 co-operate with the tube end 10 to form an anti-slip screw joint.
The inner portion 12 comprises electrically conductive portions (not
shown) electrically connecting the strip-like elements 4 to sockets 14 forming
electrical coupling means.
The connector 11 is used to enable an electrically conductive, torsion
resistant connection of a metal coupler 15 to the composite tube 1.
The coupler 15 comprises an inner, tubular portion 16 carrying
electrically conductive strips for engagement of the sockets 14. The inner
tubular portion 16 further comprises bores 18 that can be aligned with
corresponding bores 19 in the inner portion 12. By providing pins through the
bores 18, 19 a torsion resistant coupling can be achieved between the coupler
15 and the connector 11. The coupler 15 comprises a connecting sleeve 20
which can extend over the connector 11 to provide a protective shield and has
in inner thread engaging an outer thread of the connector 11 for axially urging
the connector 11 against the coupler 15 with a pre-tension.
The coupler 15 can be used for coupling to a connector 11 of a further
tube 1 or can be used to connect to drilling equipment, downhole tools or the
The tube 1 can advantageously be manufactured by means of the
thermoplastic tape winding process, in which thermoplastic tapes of composite
materials are wound onto the tubular inner liner 8 which serves as a mandrel.
The thermoplastic tape-winding process is discussed more in detail in 'On-line
consolidation of thermoplastic matrix composite tape using ultrasonic heating',
Bullock, Daniel E. and Boyce, Joseph, 39th International SAMPE Symposium
April 11-14, 1994, p 1500-1506, which publication is incorporated herein by
The tube 1 can be coiled on a reel, e.g. for transportation. The tube 1 can
be subsequently uncoiled from the reel and be inserted in a bore hole in the
ground. The use of the tubing is discussed more in detail in 'Coiled tubing
technology continues its rapid growth', Ken Newman, World Oil, January
1998, p. 64-71, which publication is incorporated herein by reference.
For spooling to a compact spool, the tube is preferably spoolable to a
radius of curvature of 3 meter or smaller and preferably 2.3 to 1.8 meters or
smaller at an outer tube diameter of 70 mm, i.e. to a radius of curvature of
about 43 times or less, and preferably about 33-26 times or less the outer tube
As is shown in Fig. 5, in operation, if the tube is to be loaded by an
internal pressure, the tube 1 is preferably spooled from a transport reel 23
onto a dispensing reel 24 having a larger diameter than the transport reel 23
before the tube is loaded with pressure. For inserting the tube 1 into the
ground, the tube 1 is uncoiled from the dispensing reel 24. Thus, the tube 1 is
loaded with internal pressure only while in a condition bent to the relatively
large radius around the dispensing reel 24. Another advantage of using a
relatively large dispensing reel is, that during repeated on-site spooling and
unspooling, the tube does not need to be bent to the relatively small radius
required for road transport, so that the life span of the tube is increased.
In Fig. 6, application of the tube 1 as smart fishing string is illustrated.
For this purpose, the tube 1 is equipped with a fishing tool 25 to be attached to
an object to be retrieved from the bore hole 26. The tube 1 is further equipped
with a load monitor 27 communicating with a load display unit 28. Because
the tube 1 is relatively light, it can easily be moved up several times to obtain
a reading from the load display unit indicating whether attachment to the
object to be retrieved has been realized. In many applications, the light weight
of the tube also makes it possible to us the force required to pull the tube
string upwards as an indication whether the tube has been coupled to the
object to be retrieved.
Fig. 7 illustrates yet another application of the proposed tube 1 with
integrated conductors 4. The tube 1 is connected to a remote subsea unit 29
which may for instance include a pump and valves powered via a hydraulic
line 30. The tube 1 and the hydraulic line 30 are connected to a production
platform 31 above sea level 33 and supported by the sea bottom 32. Since the
tube 1 can be flexed substantially, it is also suitable to be used as a riser, the
integrated power conductors 4 obviating the need of separate, and easily
damaged electric cables for controlling valves in the subsea unit 29 or,
alternatively, the need of providing a plurality of hydraulic lines controlled by
valves at the production platform.
It shall be clear that the invention is not limited to the preferred
embodiment discussed herein. In particular, the tube wall 2 may comprise a
higher or lower number of layers. Furthermore, the tube may comprise
composite layers having thermoset matrix material. Furthermore, the tube
may comprise two or more than three flexible strip-like conductors. Also, the
strip-like elements can be covered by radially inwardly and radially outwardly
disposed separate layers of non-conductive material, while the circumferential
areas between the strips are filled with a different, non-conductive material.
The strip-like elements can be provided with a non-conductive cover layer.
Advantageously, the materials of adjacent layers are chosen such that
they bond together. In particular, adjacent composite layers may comprise the
same matrix material and/or a composite layer adjacent to a non-composite
layer may comprise the material of the non-composite material as matrix
material. If two layers containing different matrix materials are to be bonded
to each other the bonding can generally be improved by providing an
intermediate layer of matrix material blended from the matrix materials of the
composite layers to be bonded.
These and other modifications will be apparent to the skilled man and
are within the scope of the invention as defined in the appended claims.