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). 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 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 "Fortran"®), 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. 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 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 15 A 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 15 A) 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. 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 3M™ Scotch- Weld™ Super 77™ and 3M™ Scotch- Weld™ 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 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 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. 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 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 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 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.