Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEMS AND PROCESSES FOR
COATING AND LINING COILED TUBING
FIELD OF THE DISCLOSURE
The present disclosure relates in general to coiled tubing commonly used in
the
petroleum industry. The disclosure relates in particular to processes for
applying a
protective material onto the inner and outer surfaces of coiled tubing.
BACKGROUND OF THE DISCLOSURE
Coiled tubing is used for many purposes in the petroleum industry, including
service as production tubing in gas wells, for pumping chemicals into an oil
or gas well,
and to carry well-logging tools or other instruments and equipment into a
wellbore. In
such applications, coiled tubing is often exposed to operational conditions
and
environments that can result in corrosion and/or abrasion of both the inner
and outer
surfaces of the coiled tubing. In some operational conditions, corrosion and
abrasion
risks can be reduced by using coiled tubing made from stainless steel, but
this is an
expensive alternative. Accordingly, it is desirable to apply a protective
coating or liner to
either or both of the inner and outer surfaces of coiled tubing to extend its
service life.
For service in some downhole environments, it may be desirable for the
protective
coating or liner to provide improved friction resistance as well.
BRIEF SUMMARY
In a first aspect, the present disclosure teaches processes for coating the
exterior
surface of continuous coiled tubing with a protective material. In some
applications, the
protective coating material may be a friction-resistant material
(alternatively referred to
herein as a low-friction or friction-reducing material, and meaning, for
purposes of this
patent specification, a material having a comparatively low coefficient of
friction such
that that the frictional resistance of an object or surface to which the
material is applied
will be reduced, as compared to the frictional resistance of the object or
surface without
the friction-resistant material).
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In a second aspect, the disclosure teaches processes for installing a
protective
tubular liner inside the bore of coiled tubing. In such processes, a tubular
liner made from
a selected polymeric material, and having an outer diameter slightly larger
than the coiled
tubing bore, is fed through rollers or dies so as to elastically deform the
liner radially and
thus reduce its outer diameter to less than the coiled tubing bore diameter.
The deformed
liner is inserted into the coiled tubing and then allowed to elastically
rebound radially,
such that the outer surface of the liner is urged into physical contact with
the inner
surface of the coiled tubing. In preferred (but not necessarily all)
embodiments of these
processes, the resultant physical contact between the outer surface of the
liner and the
inner surface of the coiled tubing will be reasonably tight and substantially
uniform, so as
to prevent or deter entry of contaminants between the outer surface of the
liner and the
inner surface of the coiled tubing.
In preferred embodiments of the lining installation process, the tubular liner
is
drawn or pulled through the coiled tubing using a leader line or other
suitable means for
facilitating the application of tension to the tubular liner. However, in
alternative
embodiments of the lining installation process the tubular liner may be pushed
into the
coiled tubing.
In some embodiments, the material used to form a protective coating on outer
surfaces of coiled tubing, or to form a protective liner for protecting inner
surfaces of
coiled tubing, may be a polymeric material comprising either a thermoplastic
material or
a thermoset material or both. The polymeric material may comprise co-polymers,
homo-
polymers, composite polymers, or co-extruded composite polymers. (As used
herein, the
term "co-polymers" denotes materials formed by mixing two or more polymers;
the term
"homo-polymers" denotes materials formed from a single polymer; and the term
"composite polymers" denotes materials formed of two or more discrete polymer
layers
that can either be permanently bonded or heat-fused.)
Polymeric materials used in processes in accordance with the present
disclosure
may comprise any one or more of various polymers. In particularly preferred
embodiments, the coating material may be high-density polyethylene (HDPE) or
cross-
linked polyethylene (PEX). Polyethylene in general has several advantages over
other
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materials such as polyurethane. For example, polyethylene has a lower
coefficient of
friction than polyurethane, it is easier to manufacture (e.g., it does not
require catalysts or
curing agents, and does not require time to cure), it is easier to recycle
than thermoplastic
polyurethane, and it is less costly. However, processes in accordance with the
present
disclosure are not restricted to the use of polyethylene or any other
particular polymeric
material; and do not exclude the use of polyurethane as a coating or liner
material.
Other polymeric materials that may be used as coating or liner materials in
accordance with the present teachings include but are not limited to
polyvinylidene
fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene
(PTFE, or
"Teflon" ), polyphenylensulfide (PPS, or "Fortron"0), polyamide (nylon),
polyester,
polyethersulfone, polyethylene terephthalate (PET), polypropylene,
polystyrene,
polyurethane, epoxy, and acetyl.
The coating or liner material may (but not necessarily will) have: an axial
modulus of elasticity exceeding 100,000 psi; low thermal conductivity;
elasticity (i.e.,
elongation before rupture) of at least 500%; and extreme high chemical
resistance, within
an operating temperature range from as low as -75 C to as high as +220 C, as
required
or desired to suit particular operational conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments in accordance with the present disclosure will now be described
with reference to the accompanying Figures, in which numerical references
denote like
parts, and in which:
FIGURE 1 schematically illustrates one embodiment of a process in
accordance with the present disclosure for applying a protective coating to
the outer surface of coiled tubing.
FIGURE 2 is an isometric view of a section of coiled tubing receiving a
protective coating on its outer surface using one embodiment of a process
in accordance with the present disclosure.
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FIGURE 3 schematically illustrates one embodiment of a process in
accordance with the present disclosure for installing a protective liner
inside the bore of coiled tubing.
DETAILED DESCRIPTION
Processes For Coating Outer Surfaces of Coiled Tubing
FIG. 1 schematically illustrates one embodiment of a process for coating the
outer
surface of coiled tubing with a protective material in accordance with the
present
disclosure, using a coating apparatus generally indicated by reference number
10. In
preferred embodiments, coating apparatus 10 includes, in sequence, a surface
preparation
stage 30, an adhesive application stage 40, an extrusion stage 50, a cooling
stage 60, and
a puller stage 70.
Uncoated coiled tubing 15A is fed from a supply reel 20 into surface
preparation
stage 30, to prepare the surface of the coiled tubing for enhanced bondability
to the
selected coating material by removing undesirable materials such as but not
limited to
mill scale, rust, dirt, grease, or other materials tending to impede adhesion
to the coiled
tubing. In accordance with one embodiment of the process, surface preparation
stage 30
uses shot peening. Alternatively or in addition, surface preparation stage 30
may involve
de-scaling, wire brushing, sand-blasting, or other suitable known surface
preparation
methods. Depending upon the properties of the coiled tubing material and the
selected
adhesive and coating materials, and also depending upon the physical condition
of the
coiled tubing as supplied, effective coating of the coiled tubing may in some
circumstances be accomplished in alternative embodiments of the process
without
requiring extensive (or any) surface preparation. Accordingly, it should be
understood
that surface preparation stage 30 is optional.
After passing through surface preparation stage 30, the uncoated coiled tubing
15A proceeds to adhesive application stage 40 where a suitable known adhesive
or
bonding agent is applied to the outer surface of the tubing. The specific
adhesive
material applied in adhesive application stage 40 will depend on the physical
properties
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and surface condition of coiled tubing 15A, as well as the properties of the
selected
coating material. Depending upon the properties of the coiled tubing material
and the
selected coating materials, and also depending upon the physical condition of
the coiled
tubing as supplied, effective coating of coiled tubing may in some
circumstances be
accomplished in alternative embodiments of the process without application of
a bonding
agent. Accordingly, it should be understood that adhesive application stage 40
is optional.
Next, the adhesive-treated coiled tubing 15A passes through extrusion
apparatus
50, which receives melted HDPE (or other selected coating material) from a
suitable
melter (not shown), which may be part of extrusion apparatus 50 or separate
from it.
Extrusion apparatus 50 (which may be of any suitable type in accordance with
known or
future-developed technology) incorporates an extrusion die (not shown)
configured to
result in the application of a preferably substantially uniform
circumferential coating of
coating material over the outer surface of coiled tubing 15A as it passes
through the
extrusion die in conjunction with a concurrent flow of melted coating material
through
the die. Typically and desirably, the coating will have a radial thickness in
the range
0.125 inches and 0.375 inches, but the coating thickness could be outside this
range
without departing from the scope of the present disclosure.
The now-coated coiled tubing (indicated by reference number 15B in FIG. 1 to
distinguish it from uncoated tubing 15A) proceeds from extrusion apparatus 50
to cooling
stage 60, where the temperature of the still-warm extruded coating is reduced
as
appropriate to solidify the coating. Cooling stage 60 may use any suitable
known means
or process for performing this function, such as (by way of non-limiting
example) passing
coated tubing 15B through a water bath, a water curtain, or an air curtain.
After exiting cooling stage 60, coated coiled tubing 15B passes through puller
stage 70, which grips coated tubing 15B and applies tractive force to pull it
through the
various stages of coating apparatus 10, without damaging the coating material.
The
finished coated tubing 15B is then wound onto a take-up reel 26. As will be
understood
by persons skilled in the art, coating apparatus 10 typically will also
incorporate suitable
idlers and guides (schematically represented by reference numbers 22 and 24 in
FIG. 1)
to facilitate the movement of the coiled tubing through the various process
stages.
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However, processes in accordance with the present disclosure are not limited
to the use of
any particular mechanism for moving the coiled tubing through the process
stages.
FIG. 2 illustrates a section of coiled tubing 15 being coated with a coating
material 55 in accordance with the process described above. An adhesive (i.e.,
bonding
agent) 45 is applied to tubing 15 in advance of the application of coating 55
to enhance
bonding of coating 55 onto tubing 15. Adhesive 45 may be selected from a
variety of
known materials, including but not limited to epoxy materials such as 3MTm
Scotch-
We1dTM Super 77TM and 3MTm ScotchWe1dTM 90.
Processes For Lining Inner Surfaces of Coiled Tubing
Processes for installing a protective liner inside coiled tubing in accordance
with
the present disclosure use a continuous tubular liner made from an elastically-
deformable
material. The outside diameter of the tubular liner in its unstressed state
(i.e., when it is
not subjected to any loadings tending to cause significant deformation) must
be slightly
larger than the bore diameter of the coiled tubing. To enable insertion of the
tubular liner
into the coiled tubing bore, the liner is fed through suitable radial
constriction means
(such as, by way of non-limiting example, rollers or dies) so as to
elastically deform the
tubular liner radially inward, such that the outer diameter of the tubular
liner, upon exiting
the radial constriction means, will be slightly less than that of the coiled
tubing bore.
Through testing, the inventors have found that reducing the outer diameter of
the
tubular liner to somewhere between 0.010 inches and 0.020 inches less than the
coiled
tubing bore diameter will typically be effective for purposes of the presently-
disclosed
processes. However, this is by way of non-limiting example only; in
alternative process
embodiments, the reduced outer diameter of the liner may be less than 0.010
inches or
more than 0.020 inches less than the coiled tubing bore diameter without
departing from
the scope of the present disclosure.
More generally, though, the required degree of radially-inward elastic
deformation
may vary according to various factors including the physical and structural
properties of
the material used for the liner. Such properties may include, by way of non-
limiting
example, the material's characteristic elastic rebound behaviour after the
removal of
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external forces that have caused the material to undergo elastic deformation,
including
how quickly or how slowly the material elastically rebounds toward its
unstressed state.
Other relevant factors may include the application of axial tension in the
liner, tending to
delay or retard the radial elastic rebound of the liner toward its unstressed
state.
After the tubular liner exits the radial constriction means (alternatively
referred to
herein as a "roll-down unit"), with its outer diameter still being reduced and
not having
rebounded to any significant extent, it is fed into one end of the coiled
tubing. Because
the coiled tubing has undergone elastic deformation by passing through the
roll-down
unit, it will want to begin elastically rebounding after exiting the roll-down
unit, tending
to expand radially outward toward its original outer diameter in an unstressed
state
(subject to rebound-inhibiting influences such as axial tension in the liner).
However,
because the tubular liner has been fed into coiled tubing that has an inner
diameter less
than the liner's unstressed outer diameter, the coiled tubing will prevent the
liner from
fully regaining its original outer diameter, and the internal elastic stresses
being relieved
(and thus tending to expand the liner radially outward) will urge the outer
surface of the
tubular liner into physical contact with the inner surface of the coiled
tubing bore.
It will be appreciated from the foregoing discussion that the amount or length
of
tubular liner that can be fed into a given length of coiled tubing will depend
on factors
such as the rate at which the radially deformed liner can be physically fed
into the coiled
tubing, and how much time is available for the feeding of additional deformed
liner into
the coiled tubing before sections of liner previously fed into the coiled
tubing have
radially rebounded sufficiently to contact the bore of the coiled tubing, thus
binding the
liner inside the coiled tubing and preventing further insertion of the liner.
This in turn
will depend on the physical characteristics and properties of the liner
material as
previously noted, and it will also depend on the degree of radially-inward
elastic
deformation undergone by the liner upon passing through the roll-down unit.
That is to
say, the greater the deformation, the more time will be available for liner
insertion before
the liner begins to bind inside the coiled tubing.
To maximize the length of time available for insertion of the radially-
deformed
tubular liner into the coiled tubing, and thereby to maximize the length of
coiled tubing
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that can be lined, one process embodiment in accordance with the present
disclosure
includes the step of feeding a free end of a leader line into a first end of
the coiled tubing
so that it exits the other (or second) end of the coiled tubing into which the
tubular liner is
to be inserted. A suitable connection or gripping means attached to the free
end of the
leader line is used to engage the tubular liner after it has passed through
the roll-down
unit. A tension force can then be applied to the other end of the leader line
(i.e., at the
first end of the coiled tubing) so as to pull the tubular liner into and
through the coiled
tubing, thus facilitating higher liner feed rates than may be possible using
some other
liner installation methods.
Preferably, the tension applied to the leader line is high enough to induce
axial
tension in the tubular liner, with the tension being reacted at the roll-down
unit (or at
another suitable location in the apparatus). As discussed previously herein,
such axial
tension in the liner will have the effect of retarding elastic rebound of the
liner, thus
further facilitating installation of the liner. Preferably, the tensile stress
induced in the
liner will be great enough to completely arrest radial elastic rebound of the
liner, such
that liner installation can proceed effectively without limit until the axial
tension in the
liner is relieved.
FIG. 3 schematically illustrates the liner installation process embodiment
described above. The free end 102 of a length of tubular liner 100 (shown for
illustration
purposes being fed from a rotatable liner reel 110) is shown exiting a roll-
down unit 120.
A leader line 130 having a first end 132 and a second end 134 is passed
through a length
of coiled tubing 200 (shown for illustration purposes on a coiled tubing reel
210).
Second end 134 of leader line 130 exits second end 204 of coiled tubing 200
and is
connected to free end 102 of tubular liner 100. First end 132 of leader line
130 exits first
end 202 of coiled tubing 200 (said first end 202 being shown for illustration
purposes as
being near the center 205 of tubing reel 210). A tension force T applied to
first end 132
of leader line 130 where it exits first end 202 of coiled tubing 200 pulls
free end 102 of
tubular liner 100 into and through the full length or a desired portion of the
length of
coiled tubing 200.
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It will be readily appreciated by persons skilled in the art that various
modifications of embodiments of systems and processes in accordance with the
present
disclosure may be devised without departing from the scope and teaching of the
present
disclosure, including modifications that may use equivalent structures or
materials hereafter
conceived or developed. It is to be especially understood that the disclosure
is not
intended to be limited to any described or illustrated embodiment, and that
the
substitution of a variant of a disclosed element or feature, without any
substantial
resultant change in operation or functionality, will not constitute a
departure from the
intended scope of this disclosure. It is also to be appreciated that the
different teachings
1 0 of the embodiments described and discussed herein may be employed
separately or in
any suitable combination to produce desired results.
In this patent document, any form of the word "comprise" is to be understood
in
its non-limiting sense to mean that any element following such word is
included, but
elements not specifically mentioned are not excluded. A reference to an
element by the
1 5 indefinite article "a" does not exclude the possibility that more than
one of the element is
present, unless the context clearly requires that there be one and only one
such element.
Any use of any form of the word "typical" is to be understood in the non-
limiting sense
of "common" or "usual", and not as suggesting essentiality or invariability.
Any use of any form of the terms "connect", "engage", "attach", or any other
term
20 describing an interaction between elements is not meant to limit the
interaction to direct
interaction between the subject elements, and may also include indirect
interaction
between the elements through secondary or intermediary structure.
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