Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
1. Field Of The Invention
[0001] The present invention generally pertains to oilfield equipment, and
more particularly to a
device and method for connecting tubing for downhole use.
2. Description Of The Related Art.
[0002] Coiled tubing is used in a broad array of applications in oilfield
operations such as drilling
and completing oil and gas wells, conveying equipment, and performing
maintenance on completed
oil and gas wells. To deploy coiled tubing into a wellbore, the coiled tubing
string is unreeled or
unspooled from a coiled tubing reel, run over an injector gooseneck and
inserted into a wellhead
system for injecting the coiled tubing into the wellbore. To retract coiled
tubing from a wellbore, the
coiled tubing is reeled or spooled back out of the wellbore through the
wellhead system over the
gooseneck and onto the coiled tubing reel. It is known that bending and
straightening the coiled
tubing in wellsite operations and spooling the coiled tubing on a reel causes
low cycle fatigue in the
coiled tubing, which if left unchecked can lead to failure of the coiled
tubing. The ability to unreel
and reel coiled tubing as a continuous tubing string nevertheless offers
attractive operational
advantages over jointed pipe that requires connections at each length of pipe.
[0003] There are occasions however when connections are required between
coiled tubing strings,
for example, in situations when the length of coiled tubing required for an
operation exceeds the
capacity of the coiled tubing reel; when the capacity of handling equipment
limits the permissible
weight of the coiled tubing reel, thereby limiting the length of coiled tubing
permitted to be spooled
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thereon; when a repair is required in coiled tubing; or when retrieving a
length of coiled tubing from
a well.
[0004] 'The problem of making coiled tubing connections between two coiled
tubing strings or
between coiled tubing and a tool or completion string has been addressed
typically in one of three
ways, those being by field welding, by using stiff connectors or by using
flexible connectors.
[0005] To connect coiled tubing string in the field, butt-welding is commonly
used. Such a weld is
made by placing together the ends of two segments of tubing, each segment
having an end cut
perpendicular to its axis, the ends being placed in line which each other
("butted" together), and a
making circumferential weld placed around the j uncture of the cut ends.
Welding in field conditions
is more challenging and less robust than the bias-type welding that is used
under controlled
conditions in coiled tubing manufacturing. Butt welded sections of coiled
tubing usually are weaker
and have much shorter low cycle fatigue life than the sections of coiled
tubing without welding:
typically a butt weld has a low cycle fatigue life in the order of 50% to 60%
of the low cycle fatigue
life of the coiled tubing. As failure of coiled tubing welds can lead to
unsafe working conditions,
verification testing using methods such as X-ray, tensile testing, or pressure
testing of the butt weld
performance is required prior to deployment of the welded coiled tubing in a
wellbore. In addition,
often connections are required in areas where explosive conditions may be
present which lead to the
need to take additional safety precautions in field welding. In sum, field
welding is a time-
consuming and operationally undesirable method for connecting two segments of
coiled tubing
together.
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[0006] Stiff connectors are used typically for connecting tools and devices to
the end of coiled tubing
such as for connecting a tool string to the end of unreeled coiled tubing
prior to insertion into the
wellbore. Stiff connectors may be used during wellbore deployment to connect
between one or more
unreeled coiled tubing strings. Stiff connectors however are not spooled with
the coiled tubing on
the coiled tubing reel as they lack the requisite flexibility to bend around
the coiled tubing reel and
deployment equipment. As a result, stiff connectors present a number of
drawbacks. Like field
welding, the use of stiff connectors in wellbore deployment requires stopping
the unreeling of the
coil tubing, installing the stiff connector into the coiled tubing, making the
connection, and then
restarting the unreeling of the coiled tubing string to deploy the connected
coiled tubing string into
the wellbore. Furthermore, stiff connectors are often larger in diameter than
the coiled tubing and
are fitted externally about the coiled tubing. As such, they cause operational
difficulties because they
do not pass through the wellhead equipment:
[0007] Stiff connectors are known that are designed to be the same diameter as
the coiled tubing or
to have an end that can be inserted into the interior diameter of the coiled
tubing; such connectors are
referred to herein as internal connectors. Internal connectors offer
operational advantages over
externally placed connectors as the internal connectors do not cause an
increased outer diameter over
the connected portion of the tubing string. Although operational difficulties
are reduced by the use
of internal connectors, the use of stiff internal connectors in coiled tubing
nevertheless poses
difficulties. Use of a stiff connector with flexible coiled tubing creates an
abrupt transition between
the connector and the tubing. As the coiled tubing is bent in routine
activities, the end of the coiled
tubing adjacent to the end of the stiff connector flexes to an undesirable
degree. This area is
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commonly called the hinge point as the bending can be so severe as to resemble
a hinged connection.
Such straining of the coiled tubing at a stiff connection can quickly make the
coiled tubing
unsuitable or unsafe for use. It is common that tubing used with a connector
becomes unsuitable for
use or fails after only a few bending/straightening cycles.
[0008] In general, stiff connectors lack the flexibility to permit them to be
spooled onto the coiled
tubing reel. On occasion, in those situations where one end of a stiff
connector is connected to the
terminal end of the coiled tubing and the connector is relatively short, it
may be possible to spool
coiled tubing onto a reel with a stiff connector attached, provided that the
opposite end of the
connector is not connected to anything. One such internal connector for
connecting one coiled
tubing string to another coiled tubing string or to a completion string (a
fixture for permanent
installation in a well) to a coiled tubing string is described in U.S. Pat.
6,474,701 issued on
November 5, 2002 to Bowles et al.
[0009] Flexible connectors are known to provide a spoolable connection for
coiled tubing strings.
One method for making a spoolable flexible connection for connecting tool
strings to a coiled tubing
string is described in U.S. Pat. 6,561,278 issued on May 13, 2003 issued to
Restarick et al. and
related U.S. Pat. 6,766,858 issued on July 27, 2004 to Restarick et al. The
external connectors
described therein are particularly applicable for use with coiled tubing made
of composite materials
and coiled tubing having a line embedded within a sidewall. In these patents,
a pair of connectors
comprising a first connector disposed about a first end of a severed tubing
string and a second
connector disposed about a second end of a severed tubing string is used to
connect one or more well
tool assemblies to the coiled tubing.
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[0010] Another type of internal flexible connector for use with coiled tubing
is described in SPE
89527, Luft, H.B., et al., entitled Development of a New Spoolable Mechanical
Coiled Tubing
Connector, March 2004. As described therein, this flexible connector uses
composite materials,
including an elastomeric middle section to provide flexibility, and entails a
construction having
composite materials and using both super alloy steels and elastomers
backfilled into the outer
diameter of the connector. The flexible connector described in SPE 89527 has
transition sections on
either end of the connector where the coiled tubing overlaps the connector.
According to Luft et al,
testing of this connector indicated that the low cycle fatigue performance of
the connector/coiled
tubing combination provided a life span for the combination of 39% to 69% of
the life span for the
coiled tubing alone.
[0011] Testing required for confirming that the materials from which a
connector is made are
compatible for use in a downhole environment and for oilfield operations also
is discussed in SPE
89527. Coiled tubing connectors, like the coiled tubing itself, need to be
compatible with the
environment in which they will be used. Testing is required to demonstrate
that significant
degradation to or failure of the coiled tubing connector will not result from
exposure to wellbore
environments. For example, coiled tubing may used for delivering acid
treatments to subterranean
formations, or in environments in which elevated levels of H2S are present.
The acid testing
reported in SPE 89527 on various connector materials shows this compatibility
can vary. To avoid
the cost and time required for compatibility testing, it would be advantageous
to construct an internal
flexible connector from materials having the same or similar chemical
resistance as the coiled tubing.
As a general matter, it would be more cost effective to construct an internal
coiled tubing connector
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from readily available commercial materials rather than specialty products
such as those used in the
connector described in SPE 89537.
[0012] A particular challenge to using a flexible connector and coiled tubing
made of conventional
materials is the varying range of material properties generally accepted in
materials such as
commercial grade steel used to make coiled tubing. These materials normally
are produced with a
10-20% tolerance for yield strength. For example, 4140 (18-22 Rc) steel is
known to have a yield
strength between 80,000 psi and 95,000 psi. This variation in yield strength
is the foundation for
design limitations between the connector and the coiled tubing. For example,
if one of the
components has a yield strength near the minimum allowed ("low yield
component") and the other
component has a yield strength near the maximum allowed ("high yield
component"), the strain in
the components under the same conditions would differ, leading to differing
low cycle fatigue lives.
In such situations, when the low yield component reaches the yield point, the
low yield component
begins to deform plastically but the high yield component remains in its
elastic range and does not
yield. By the point at which the yield point of the high yield component is
reached and the high yield
component begins to deform plastically, the low yield component already has
deformed significantly.
For example, for a conventional material such as 4140 steel having minimum and
maximum yield
curves as shown in FIG. 1, at a stress of 100 ksi, low yield component would
have as much as 4%
strain while the high yield component would have a strain of about 0.5%. Since
low cycle fatigue
life is closely related to the amount of cyclic strain, the low yield
component will fail significantly
sooner than the high yield component.
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[0013] The flexible connectors that are known, such as that disclosed in SPE
89527, have a flexible
section in the center of the connector. This middle flexible section is
designed to have a bending
stiffness similar to that of the coiled tubing. The end sections on either
side of the flexible center
section are much stiffer than the coiled tubing. The design theory behind such
a configuration is to
provide a flexible center section of the coiled tubing connector that deforms
similarly to the coiled
tubing itself under the same amount of strain. The low cycle fatigue
performance of these flexible
connectors depend both on the stiff end connections providing a gradual
transition between the
flexible coiled tubing and the flexible center section of the connector and on
the flexible centers
section having similar stiffness and fatigue life to the coiled tubing.
Therefore it is crucial to the
performance of these flexible connectors designed with flexible center
sections that both flexible
center section of the connector and the coiled tubing strain equally. This is
not easily achieved given
the variation of material properties and the varying stress/strain conditions
along the bend distance
between the flexible section of the connector and the length of the coiled
tubing string beyond the
influence of the connector end section. It has been observed that coiled
tubing connectors that use a
flexible section between two stiff end connections often have inconsistent
performance and
periodically fail much sooner than expected.
[0014] Therefore, there exists a need for improved methods and apparatus for
connecting coiled
tubing. In carrying out the principles of the present invention and
embodiments thereof, methods and
apparatus are provided which solve the problems in the prior art.
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SUMMARY OF THE INVENTION
[0015] The present invention provides a method of connecting a first tubing
and a second tubing
using an internal tubing connector having a bore, the connector having a first
end section having a
tapered outer surface and stiff section wherein the stiff section of the
connector is secured to the first
and second tubings. In some embodiments, the internal surface of the connector
along the bore is
also tapered. In some embodiments, a second end section having a tapered
external surface is also
provided and disposed within the second tubing. In preferred embodiments, at
least one of the first
tubing or second tubing is coiled tubing, and in particular embodiments, both
of the tubings are
coiled tubing. In the methods of the present invention, at least one of the
first or second tubings may
be spooled on a reel. The connector and method of connecting of the present
invention is useful
particularly in making repairs in coiled tubing, wherein a section of coiled
tubing is damaged or
removed and the apparatus and method of the present invention is used to
repair, patch or generally
connect the two sections of coiled tubing between which a portion of tubing
has been damaged or
removed.
[0016] The connector apparatus of the present invention useful for connecting
a first and a second
section of tubing comprises a body with a longitudinal bore therethrough, a
first end section, and a
stiff section; the first end section of the connector having a tapered outer
surface; and the exterior of
the stiff section adapted to be connected to the inner diameter of a first and
a second tubing. In some
embodiments, the connector may further comprise a second end section, the
second end section
having a tapered outer surface and the stiff section being disposed between
the first and the second
end sections. The first or second end section may further comprise a tapered
internal surface along
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the bore. An annular lip may be provided about the body and adapted to be
disposed between ends
of the first and second sections of tubing. One or more seals may be disposed
between the connector
body and the first or the second, or both, tubings. The stiff section of the
connector of the present
invention may be secured within the first and second tubings by engaging the
exterior surface of the
body with the inner surface of the tubing using a plurality of indentations,
grooves, ridges, punch
hole, or other connective means. In some embodiments, a debris barrier is
provided between at least
one end section of the connector and the tubing.
(0017] The present invention in specific embodiments relates to a method of
deploying coiled tubing
in a wellbore comprising providing a coiled tubing connector having a body
with a bore throughout,
the body having first and second end sections with tapered external surfaces
and a stiff section
disposed between the first and the second end sections; placing one end
section into a first coiled
tubing section, placing the second end section into a second coiled tubing,
securing the stiff section
to the inner diameter of the first and second coiled tubings to form a
connected tubing and lowering
the connected tubing into a wellbore. The method may further comprise
retrieving the coiled tubing
from the wellbore. The first or second coiled tubing may be disposed on a
reel. Similarly, the
connected coiled tubing may be disposed on a reel. In some embodiments, the
connector may
comprise an annular lip disposed about the body and adapted to be disposed
between ends of the first
and second sections of coiled tubing and in some embodiments, the connector
may comprise at least
one barrier to prevent debris from entering between the end section and the
coiled tubing.
[0018] Other features, aspects and advantages of the present invention will
become apparent from
the following discussion.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a representative stress/strain curve for a grade of steel.
[0020] FIG. 2 is side view of a specific embodiment of a coiled tubing
connector constructed in
accordance with the present invention and in use to connect a section of
coiled tubing to a tool string.
[0021] FIG. 3A is a side view of another specific embodiment of a coiled
tubing connector
constructed in accordance with the present invention similar to the one shown
in FIG. 2 but shown
not connected to any coiled tubings.
(0022] FIG. 3B is a side view of another specific embodiment of a coiled
tubing connector
constructed in accordance with the present invention.
[0023] FIG. 3C is a side view of another specific embodiment of a coiled
tubing connector
constructed in accordance with the present invention.
[0024] FIG. 4 is side view of two coiled tubing connectors constructed in
accordance with the
present invention, and in use to connect coiled tubing to a tool string.
[0025] FIG. 5 is a side view of a specific embodiment of a coiled tubing
connector constructed in
accordance with the present invention, and in use to connect two sections of
coiled tubing to a tool
string.
[0026] FIG. 6A is a strain diagram from a finite element model of a prior art
internal coiled tubing
connector having a flexible center section.
[0027] FIG. 6B is a strain diagram from a finite element model of an
embodiment of a coiled tubing
connector according to the present invention.
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[0028] FIG. 7 is side view of another specific embodiment of a coiled tubing
connector constructed
in accordance with the present invention, and in use to connect two sections
of coiled tubing.
[0029] While the invention will be described in connection with the preferred
embodiments, it will
be understood that it is not intended to limit the invention to those
embodiments. On the contrary, it
is intended to cover all alternatives, modifications, and equivalents as may
be included within the
spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0030] Referring to the drawings in detail, wherein like numerals denote
identical elements
throughout the several views, there is shown in FIG. 2 a coiled tubing
connector 10 constructed in
accordance with the present invention and in use to connect a first section of
coiled tubing 12 and a
second section of coiled tubing 14. The connector 10, having a body 16 having
a longitudinal bore
18 therethrough, comprises a stiff section 27 and at least one end section 28.
Often stiff section 27
is provided between two end sections 28, as is shown FIG. 2. In some
embodiments, body 16 of
connector 10 may be discontinuous, and in further embodiments, stiff section
27 is separable from
one or more end sections 28. It is preferred for embodiments for connecting
two sections of coiled
tubing such as that shown in FIG. 2 that body 16 of connector 10 is a
continuous body in which one
region of connector body 16 is stiff section 27 and other region or regions of
connector body 16 are
end section or sections 28. Such an embodiment is particularly useful to be
placed between a first
section of coiled tubing 12 and a second section of coiled tubing 14 to form a
repair between the two
section, for example when an area has been damaged, stressed, or is of
inferior quality.
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[0031] The stiff section 27 of connector 10 has an outer diameter that it will
fits snugly within the
inner diameter of first and second sections of coiled tubing 12 and 14. The
exterior diameter of body
16 remains essentially constant throughout stiff section 27, excepting in
localized areas where a
means, such as a groove or indentation, to effect a connection with coiled
tubing 12 and 14 are
present.
[0032] In end sections 28 of body 16, external diameter 29 of body 16
gradually decreases from the
end 31 of the end section 28 proximate to the stiff section 27 towards the
distal end 33 of the body
16, such that the external diameter of end section 28 of body 16 is not
engaged snuggly within the
interior diameter of coiled tubing 12 or 14. When coiled tubing 12 and 14 is
straight, end section 28
is not in contact with the inner diameter of the coiled tubing 12 or 14 owing
to the decreasing
external diameter 29 of end section 28. This decreasing external diameter,
referred to herein as
tapered, may be constructed in any vaxiety of ways that provides a smaller
external diameter at the
distal end 33 of end section 28; examples of ways by which a taper may be
formed include but are
not limited to a single angle, a series of short angle sectors, a constant
radius, or a compound radius.
[0033] As coiled tubing 12 is connected to connector 10 in stiff section 27
and coiled tubing 12
bends as is routine in coiled tubing deployment and operation, only a limited
area of end section 28
will be in contact with the interior diameter of coiled tubing 12 as it bends
owing to the decreasing
exterior diameter 29 of end section 28. In this way, there is a limited area
of contact between coiled
tubing 12/14 as it bends over the length of end section 28 and that limited
area of contact translates
along the length of end section 28 as coiled tubing 12 bends. As such, the
stress point occurring at
the point of contact translates along the end section 28 and overlapping
coiled tubing 12, thereby
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avoiding the formation of a specific point of stress concentration or hinge
point. This characteristic
of the present invention is referred to herein as the restrictive bend
feature.
(0034] The restrictive bend feature avoids the formation of a hinge point
resulting from stress
repeatedly concentrating in areas. It is known that such hinge points create a
week point in coiled
tubing connectors. By design, this restrictive bend feature provides a
transition between the stiff
section 27 of connector 10 and the coiled tubing 12 or 14 and distributes the
strain in the coiled
tubing over the length of end section 28 rather than in a localized hinge
point. By such a strain
distribution, the maximum stress imposed on any particular point of coiled
tubing 12 or 14
overlapping end section 28 and the duration of time at which any particular
point is subj ected to that
stress is reduced. This serves to improve the low cycle fatigue performance of
the overall coiled
tubing and connector configuration. Such a configuration is notably different
from known flexible
internal connectors and is counter to the conventional approach of providing a
flexible middle
section with stiffer section on either side. Thus the coiled tubing connector
of the present invention
is useful to provide a connection that is flexible on both ends and stiff in
the middle.
[0035] In various embodiments, the diameter of the internal surface of body 16
along longitudinal
bore 18 in end section 28 may decrease in a similar manner to external
diameter 29, may remain the
same throughout end section 28, or may increase to form an internal tapered
surface 30. In
embodiments in which the diameter of the internal surface of body 16 along
longitudinal bore 18 in
end section 28 remains the same or increases, the cross sectional wall
thickness of body 16 in end
section 28 decreases toward distal end 33 as a result of decreasing external
diameter 29. This
decreasing wall thickness makes end section 28 more flexible at distal end 33
and increasingly less
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flexible along the length of end section 28 extending to the end of stiff
section 27. In this way,
connector 10 is most flexible at the distal end 33 of end section 28 and has
diminishing flexibility
traversing toward stiff section 27 along the length of end section 28 such
that the stiffest area of end
section 28 is at end 31 adjacent to stiff section 27.
[0036] Connector 10 may be secured to the coiled tubing 12 and 14 in stiff
section 27 by techniques
suitable for use with internal connectors such as roll-on connectors, screws,
crimping, and dimpling.
In FIG. 2, the connection between stiff section 27 and coiled tubing 12 and 14
is shown made by
indentations 22 on the outer surface of stiff section 27 receiving
protuberances 20 on the coiled
tubing 12 and 14. Such indentations may be made a variety of ways such as
surrounding the coiled
tubing with a mold and pressing the mold to form indentations, using a push or
screw to form the
indentations, or using a pre-pattern of weaker points in stiff section 27 into
which coiled tubing 12 or
14 may be easily pressed. In some embodiments, the exterior surface of stiff
section 27 may be
patterned in a manner to facilitate this connection with coiled tubing 12 and
14. For example,
indentations in the exterior surface of stiff section 27 may spread uniformly
about the circumference
in a localized area or along the length of stiff section 27. Alternatively,
depressions for receiving
screws holes may be provided in the exterior surface of stiff section 27; such
depressions may
similarly be in a localized area or along the length of stiff section 27.
[0037] In addition, the pattern, shape, or depth of such indentations may be
varied and in particular,
be varied in such a manner that the stress during bending of the connection is
distributed across the
indentations and not concentrated in a limited localized area. Moreover this
variation may be done
in such a manner as to vary the relative snugness of the connection between
connector 10 and coiled
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tubing 12 or 14 across stiff section 27 of connector 10 such that the
connection between connector 10
and coiled tubing 12 or 14 is relatively snug near the ends of coiled tubing
12 or 14 and the
connection is less snug in other areas of stiff section 27 of connector 10.
For example, dimple
screws closest to the ends of coiled tubing 12 or 14 of the tubing can be
tightened to a different depth
compared to those screws furthest from the ends of coiled tubing 12 or 14.
[0038] Alternatively or in addition to indentations along the external surface
of stiff section 27,
indentations may be provided on the internal surface of body 16 along
longitudinal bore 18. In this
manner, a thinner wall section of body 16 is provided in desired locations at
which coiled tubing 12
or 14 may be pressed or crimped to secure contact between connector 10 and
coiled tubing 12 or 14.
In another embodiment, a groove may be provided around the circumference of
stiff section 27 or a
series of circumferential or partially circumferential grooves may be placed
or staggered along the
length of stiff section 27. Various combinations of these techniques may also
be used and are
considered within the scope of the present invention.
[0039] Connector 10 may preferably be provided with one or more seals 24 to
prevent fluid leakage
between the connector 10 and each of either or both of the coiled tubing
12/14. These seals 24 may
be of any known type, including but not limited to O-rings, chevron seals, T-
seals, dynamic seals
such as PolyPakTM, and various other elastomeric devices.
[0040] In specific embodiments, the present connector 10 may include an
annular lip 26 disposed
about the body 16 in the stiff section 27 and positioned such that it is
disposed between the
respective ends of the coiled tubings 12 and 14. The diameter of annular lip
26 is the same or
essentially equivalent to the outer diameter of coiled tubing 12 and 14. As
such, annular lip 26 does
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not preclude connector 10 from passing through the wellhead equipment. Annular
lip 26 provides
support for the end of the coiled tubing 12 or 14 or to reduce forces that
cause flaring of tubing ends
and also to contain and protect the tubing ends. As will be appreciated by
those of skill in this art,
the annular lip 26 functions to reduce deformation or "egging" of the ends of
the coiled tubing 12 or
14 during use.
[0041] In some embodiments, a flow control device, such as a check valve, may
be used in
conjunction with connector 10. The flow control device permits fluid flow
through in one
configuration and restricts fluid flow through in another configuration.
Methods of switching such
flow control devices from one configuration to another configuration are well
known and include, for
example, exerting an axial external pressure on the connector, dropping a
ball, or providing a control
signal. Such embodiments are of particular use when the coiled tubing is under
pressure, such as
well pressure or fluid pressure. The flow control device may be placed within
stiff section 27 of
connector 10 or within coiled tubing 12 or 14 adjacent to connector 10. A
combination of internal
and external flow control devices may be also used.
[0042] As shown in FIGS. 3A through 3C, the decreasing exterior diameter 29 of
end section 28 can
be constructed on the external surface of body 16 in a variety of ways,
including but not limited to
with a single angle, a series of short angle sectors, a constant radius or a
compound radius. In some
embodiments, the diameter of the internal surface of body 16 along
longitudinal bore 18 may
increase in end section 28 to form an internal tapered surface 30. For
example, in the specific
embodiments shown in FIG. 2, end section 28 is shown having an outer tapered
surface 29 and a
tapered internal surface 30 in longitudinal bore 18. This internal tapered
surface 30 similarly may be
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constructed in a variety of ways, including but not limited to with a single
angle, a series of short
angle sectors, a constant radius, or a compound radius. In some embodiments,
the manner in which
decreasing exterior diameter 29 and internal tapered surface 30 are
constructed may be the same and
in some embodiments, the manner in which they are formed may be different. In
the specific
embodiment shown in FIG. 3A, end section 28 includes an internal tapered
surface 30 and a tapered
outer surface of body 29. In the embodiment shown in FIG. 3B, end section 28
includes a plurality
of outer tapered surfaces, or short angle sectors, 29A, 29B and 29C, and
internal surface 30 is not
tapered. In the embodiment shown in FIG. 3C, end section 28 includes a tapered
outer surface 29
formed by a constant radius and internal surface 30 in the longitudinal bore
18 is not tapered.
[0043] There is shown in FIG. 4 a coiled tubing connector 10 constructed in
accordance with the
present invention and in use to connect a first section of coiled tubing 12
and a tool string 13.
Connector 10 has a body 16 having a longitudinal bore 18 therethrough and
comprises a stiff section
27 and an end section 28. In some embodiments, connector 10 may disassembled
by separating stiff
section 27 may be separated from end section 28 and assembled by attached
stiff section 27 to end
section 28 by using any number of connection methods known for connecting
while maintaining a
flush exterior surface such as threading, patterned jointing, or lock and key.
[0044] Stiff section 27 of connector 10 has an outer diameter that fits snugly
within the inner
diameter of coiled tubing 12. The other end 41 of stiff section 27 connects to
tool string 13. Such a
connection to tool string 13 may be made by any number of connection methods
known for
connecting while maintaining a flush exterior surface such as threading,
patterned jointing, or lock
and key. In end section 28, the external diameter 29 of body 16 gradually
decreases from end of the
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end section 28 proximate to the stiff section 27 towards the distal end 33 of
the body 16, such that
the external diameter 29 of end section 28 at the distal end 33 of body 16 is
not engaged snuggly
within the interior diameter of coiled tubing 12. When coiled tubing 12 is
straight, end section 28 is
not in contact with the inner diameter of the coiled tubing owing to its
decreasing external diameter
29. In this way, there is a limited area of contact between coiled tubing
12/14 as it bends over the
length of end section 28 and that limited area of contact translates along the
length of end section 28
as coiled tubing 12 bends. As such, the stress point occurring at the point of
contact translates along
the end section 28 and overlapping coiled tubing 12, thereby avoiding the
formation of a specific
point of stress concentration or hinge point. The restrictive bend feature of
end section 28 previously
described is present in the embodiment shown in FIG. 4.
(0045] A specific embodiment is shown in FIG. 5 in which two coiled tubing
connectors 10
constructed in accord with the present invention are shown to connect a first
section of coiled tubing
12, a tool string 13, and a second section of coiled tubing 14. Each coiled
tubing connector 10 has a
body 16 having a longitudinal bore 18 therethrough and comprises a stiff
section 27 and an end
section 28. Each tubing connector 10 is connected to coiled tubing 12 or 14 at
stiff section 27 and to
tool string 13 at one end 41. The first tubing connector 10 is connected at
stiff section 27 to coiled
tubing 12 and the second tubing connector 10 likewise is connected at stiff
section 27 to coiled
tubing 14. Stiff sections 27 have an outer diameter that fits snugly within
the inner diameter of coiled
tubing 12. End section 28 of each of the first and the second tubing connector
10 has an external
diameter 29 that gradually decreases from the end 40 of the end section 28
proximate to the stiff
section 27 towards the distal end 33 of the body 16, such that the external
diameter 29 of end section
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28 at the distal end 33 of body 16 is not engaged within the interior diameter
of coiled tubing 12 or
14 respectively when the coiled tubing is not bent.
[0046] In some embodiments, first or second connector 10, or both, may
comprise a body 16 in
which one region of the body 16 is stiff section 27 and another region of body
16 is end section 28.
In other embodiments, body 16 of the first or second connector 10, or both,
may disassembled by
separating stiff section 27 from end section 28 and assembled by attached
stiff section 27 to end
section 28 using any number of connection methods known for connecting while
maintaining a flush
exterior surface such as threading, patterned jointing.
[0047] Stiff section 27 of each the first and second connectors 10 have an
outer diameter that fits
snugly within respectively the inner diameter of coiled tubing 12 or 14. End
section 28 of each of the
first and the second tubing connector 10 has an external diameter 29 that
gradually decreases from
the end 31 of the end section 28 proximate to the stiff section 27 towards the
distal end 33 of the
body 16, such that the external diameter 29 of end section 28 at the distal
end 33 of body 16 is not
engaged within the interior diameter of coiled tubing 12 or 14 respectively
when the coiled tubing is
not bent. This restrictive bend feature of end section 28 previously described
is included in the
embodiment shown in FIG. 5.
[0048] Each of the embodiments described has a reduction in the exterior
diameter of end section 28.
When bending occurs in routine use, coiled tubing 12/14 bends until it
contacts end section 28. As
bending continues, the contact point between coiled tubing 12/14 and end
section 28 translates along
the length of end section 28, thereby avoiding a localized hinge point. In
this way, connector 10 of
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the present invention undergoes lower strain during bending and as a result,
suffers lower fatigue and
has a longer useful life.
[0049] Advantages of the present invention may be seen by referring to FIGS 6A
and 6B in which
output from f nite element modeling is shown. FIG 6A illustrates the output of
finite element
modeling of a known internal coiled tubing connector having a flexible center
section and stiff end
sections; numerous areas of high strain concentration 50 are shown including
an extended area of
high strain concentration 50 in the flexible center section. FIG 6B
illustrates the output of finite
element modeling having the same inputs as FIG 6B, except that the connector
is modeled is of the
present invention; few areas of high strain concentration 50 are shown for the
present invention
connector. As high strain concentration leads to diminished usage life or to
greater risk of failure,
the advantages of the connector of the present invention are apparent from a
comparison of FIG. 6B
to FIG 6A from which is can be seen that connector 10 of the present invention
undergoes less strain
than the coiled tubing connector having a flexible center section.
[0050] As shown in FIG. 7, in another specific embodiment, connector 10 may
further be provided
with a flow guide/debris barrier 32 disposed at each end of the connector 10.
The barrier 32 may
include a body 34 with a tubular section 36 extending therefrom and adapted to
fit within the bore 18
of the connector 10. The body 34 may include a shoulder 38 designed to engage
the tip of end
section 28 of connector 10. Body 34 may include an annular recess 44 for
receiving an annular seal
42. The body 34 may further include a tapered inner bore 40. The debris
barrier 32 functions to
keep debris and solids, which could impede controlled bending, out of the
restrictive bend area
between external diameter 29 of end sections 28 and internal surface 30 of the
coiled tubings 12/14.
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Barrier 32 may be separate from the connector 10, as shown, or it may be
integral with the connector
10. In various embodiments, barrier 32 may be rigid or flexible. An example of
an integral flexible
embodiment is an elastomeric cone molded to the end of connector 10. Any
combination of these
techniques may be used. If barrier 32 is separate from connector 10 instead of
integral with it, it may
be held in position by a coiled tubing weld bead 46 on one side and connector
10 on the other side.
FIG. 7 further illustrates that connector 10 may include an anti-extrusion
ring 48 adjacent seal 24.
(0051] It can be seen in light of the above description of the tubing
connector of the present
invention and related methods that the present invention represents an
improvement over prior coiled
tubing connectors and methods. Advantages of the present invention include a
tensile strength
similar to the tensile strength of the coiled tubing; the capability of
bending around a coiled tubing
reel and an injector gooseneck during operation; have a low cycle fatigue life
similar to the coiled
tubing; providing a pressure tight seal both from internal and external
sources; and passing through a
wellhead assembly.
[0052] Although the embodiments herein have been described with respect to
coiled tubing, one
skilled in the art would understand that although the present invention is
useful in application for
connecting any tubing, notwithstanding its particular usefulness in coiled
tubing applications.
(0053] Although only a few exemplary embodiments of this invention have been
described in detail
above, those skilled in the art will readily appreciate that many
modifications are possible in the
exemplary embodiments without materially departing from the novel teachings
and advantages of
this invention. Accordingly, all such modifications are intended to be
included within the scope of
this invention as defined in the following claims. In the claims, means-plus-
function clauses are
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intended to cover the structures described herein as performing the recited
function and not only
structural equivalents, but also equivalent structures. Thus, although a nail
and a screw may not be
structural equivalents in that a nail employs a cylindrical surface to secure
wooden parts together,
whereas a screw employs a helical surface, in the environment of fastening
wooden parts, a nail and
a screw may be equivalent structures. It is the express intention of the
applicant not to invoke 35
U.S.C. ~ 112, paragraph 6 for any limitations of any of the claims herein,
except for those in which
the claim expressly uses the words 'means for' together with an associated
function.
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