NO318444B1 - Flushable composite counter body. - Google Patents

Description

The present invention relates to coilable composite pipes.

Spiral coiled steel tubing has a number of applications in oil well operations. They are used, for example, to lead wire rope down the borehole with well tools, such as logging tools and perforating tools. Such pipes are also used in the overhaul of wells, to deliver various chemicals down the wellbore and to perform other functions.

Spiral-rolled steel pipes can be coiled because the steel used in the product has a high ductility (ie ability to deform plastically without breaking). The coiling operation is most often performed while the pipe is under high internal pressure, which introduces combined stress effects. Unfortunately, repeated coiling and use will cause fatigue damage, and the spiral-rolled steel pipe may suddenly fracture and fail. The dangers of the operation and the risk to personnel and the high financial costs of errors in the form of downtime to carry out fishing operations, make it necessary to take the product out of service before the expected error, after relatively few trips into the well. The cross-section of the steel pipe expands during repeated use, resulting in reduced wall thickness and higher bending strength with a corresponding reduction in the ability to withstand pressure. Spiral-rolled steel pipes are limited to internal pressures of up to 350 kg/cm. Higher pressure means a significant reduction in the pipe's integrity, so that it will not withstand continuous bending, thus limiting the pipe's lifetime, even for a single field application.

It is therefore desirable to produce a spirally rolled pipe which is not of steel, and which is able to be used and coiled under borehole conditions, which does not suffer from the limitations of steel pipe, and which is highly resistant to chemicals.

In addition, current logging operations through spiral-rolled steel pipe sometimes use a wire cable that is fed into the spiral-rolled steel pipe to transmit data, or when contemporaneous data is not required, a logging tool that can collect and store data in the borehole. When contemporary data is required, a dedicated coil of spiral-rolled pipe is used with the wire permanently installed in the pipe. This takes up significant cross-sectional space within the tube, making the coiled tube unsuitable for other operations that require a flow path or open hole through the tube. Fluids are sometimes transported from the surface to a downhole location through pipe, to produce a means to treat formations or to operate a mud motor to drill through the formation. In addition, it may be desirable to pump devices through the coiled pipe to a location in the borehole, for various operations. An open bore in the spirally rolled pipe is therefore essential for many operations, and for this reason it is desirable not to have electrical conductors or the like placed inside the open bore in the pipe.

External pressure on the spirally rolled pipe is also an important stress condition, and can be over 175 kg/cm<2>.

US 3 554 284 (Nystrøm) describes the use of a logging cable in which two inner layers of fibers are wound at ±18°, and two outer layers are wound at ±35°.

US 4,255,820 (Rothermel et al.), describes a band prosthesis designed with a tightly woven cylindrical core which provides axial rigidity to the prosthesis.

US 4,530,379 (Policelli) describes a composite fiber tube with a transition to a metal coupling. The fibers can be graphite, carbon, aramid or glass. These fibers, in one embodiment, are alternately laid in ±15° orientation with the longitudinal axis. In the embodiment of Figure 4, "a wider choice of axial angles for the filaments in the layers" is allowed. Furthermore, "this design can be used in a fluid transport pipe that has bending loads in addition to the internal pressure loads, and in structural parts that need bending and axial stiffness". Policelli suggests that the fiber angles can be chosen in a range between 5° and 75° as measured from the axis.

US 4,556,340 (Morton) describes the use of an externally mounted strip on a flexible pipe. The strip can be of any material that has high axial stiffness in tension and low axial stiffness in compression. The strip provides supported bending or bending about a preferred axis.

US 4,728,224 (Salama) describes a composite tension mooring line on separate layers of carbon fibers and aramid fibers, where the fibers are axially or spirally wound at a low angle. A layer of fibers wound at 90° can be arranged as an outer sheath.

US 4,336,415 (Walling) shows a composite tubing assembly for use in a wellbore, with arrangements for transporting production fluids and electrical wiring.

US 3 604 461 (Matthews) relates to a multilayer high-pressure hose which can slide at the core, ie on the inner liner, but which is tightly bound at the periphery. The layers of fibers cross each other and are arranged to prevent migration of the binding agent through the layers to prevent the liner from being attached to the outer layers of fibers. The structure of the fiber layers is thus arranged to move in relation to the lining or the inner tube of the hose.

US 3 856 052 (Feucht) shows a flexible hose with reinforced areas in the side walls and parallel to the longitudinal axis to provide tensile strength in the longitudinal direction. This means that the hose easily collapses through an axis and can easily be coiled on itself.

US 646 887 (Stowe et al.) has one or more conductors inserted into a side wall of a hose.

Most prior art tubular structures, which are designed to be coiled and also to transport fluids, are made like a hose whether they are called a hose or not. For example, the Feucht structure according to US 3,856,052 has longitudinal reinforcements in the sidewalls so that a flexible hose can collapse preferentially in a plane, however, the construction is a classic hose with vulcanized layers of polyester which is not able to carry compression loads or high external pressure loads. Tubing typically uses an elastomer such as rubber to hold the fibers together, but does not use a high modulus plastic binder such as epoxy. Hoses are designed to bend and carry internal pressures, but are not normally subjected to external pressures or high axial compressive or tensile loads. For an elastomer-type material used in hoses, the elongation at break is so high (typically more than 400%), and the work response so non-linear, that it is common practice to define a modulus corresponding to a specified elongation. The modulus of an elastomeric material corresponding to 200% elongation is typically in the range of about 2 to 13.8 MPa (300 psi to 2,000 psi). The modulus of elasticity for a typical plastic matrix material used in composite piping is from 690 to 3,473 MPa (100,000 to 500,000 psi) or more, with representative strains to failure ranging from 2% to 10%. This large difference in modulus and elongation to break between rubber and plastic, and thus between hoses and composite pipes, is what allows a hose to easily collapse into an essentially flat state under relatively low external pressures, eliminating the ability to carry high axial tensile or compressive loads, while the higher modulus characteristic of the plastic matrix material used in composite pipes is sufficiently stiff to transfer loads into the fibers and thus withstand high external pressures and axial tension and compression without collapse. The procedure for constructing a composite pipe to resist high external pressures and compression loads involves the use of complex technical principles of composite mechanics to ensure that the pipe has sufficient strength. It has not previously been considered possible to build a true composite pipe capable of bending to a relatively small diameter, and of being able to carry internal pressures and high tensile and compressive loads in combination with high external pressures. In particular, a hose would not be able to withstand high compression loads and external pressure loads.

US 3,604,461, on the other hand, shows a tubular part for carrying relatively high internal pressures, but which is still a hose made of layers of fibers connected by adjacent fiber windings. The fibers and layers are attached with an adhesive, but the adhesive does not impregnate the fibers, so that the adhesive penetrates to the plastic core. Matthews shows placement of the fibers so that they do not shift relative to each other, but flexibility would be damaged if the adhesive would surround the fibers and layers. If the fibers are not individually surrounded by the matrix, the fibers would not have the ability to carry significant compressive loads or external compressive loads, a characteristic essential to the performance of the invention in coiled tubing applications requiring bending as well as pushing of the tubing and the ability to resist external pressure. In this context, Matthew shows that the liner does not have to be the bond to the hose. Matthew's structure would allow high external pressures to penetrate the liner plastic core and collapse it.

The references that show the use of electrical conductors in a hose do this by making them inserts in the walls of the hose and not as integral structural parts that function to strengthen the hose and give it special structural qualities. The electrical and optical conductors are located at or near the minimum moment of inertia to isolate them from significant bending stresses that would be exerted during bending if they were located elsewhere. Prior art hoses with conductors are not particularly concerned with protecting the conductors against bending forces exerted during coiling of the hose, since the hose can be flattened to reduce the effect of bending. In the present invention, the pipe must be held generally circular and be able to resist collapse when high bending stresses are exerted during coiling, and when the pipe bulges as it is pushed into the wellbore.

In the described embodiments of the invention, composite pipes are arranged for borehole operations such as for use during well logging and overhaul operations in oil wells. The pipe, which is preferably coilable, comprises a composite pipe part with an outer composite structure containing strong and rigid fibers embedded in a resin material such as epoxy. The fibers are oriented to resist internal and external pressures and to provide low bending stiffness. Two inner regions in the outer structure are located near the neutral axis of the tube part, and located in diametrically opposite walls of the outer composite structure to form selective reinforcements within these opposite walls. The inner regions define a minimum moment of inertia for bending that extends diametrically through the inner regions, and a maximum moment of inertia for bending that is generally orthogonal to the minimum moment of inertia, where the inner regions comprise composite structures oriented far from the axis of the tube to provide a high axial stiffness and strength to the outer tubular part, so that the composite tubular part has significantly greater bending stiffness around the major axis compared to the bending stiffness around the minor axis to thereby provide a preferred bending direction for the composite tubular part when it is coiled and uncoiled. The arrangement of fibers or other structural materials in said inner area is oriented to form a high axial stiffness, high compressive and tensile strength and low bending stiffness to counteract shear stresses. High strength and modulus fibers are embedded in and banded in a matrix that holds the fibers in place, acts as a medium for load transfer and protects the fibers from environmental damage. The plastic agent in which the fibers are embedded to form the matrix will have a modulus of elasticity (hereafter modulus) exceeding 689 MPa (100,000 psi). The liner also serves as a pressure retaining part to prevent leakage of internal fluids inside the pipe. In one configuration, the liner has a circular bore that is required in some borehole operations. In other embodiments, the liner is made concave to accommodate selective reinforcement members in the sidewalls of the outer structure, which in turn allows the exterior surface of the composite spirally rolled tube to be approximately circular.

The outer composite structure consists of several layers or plies of oriented fibers laid as described in a matrix, which outer composite structure is bonded to a liner such that the liner is integrally attached to the outer composite structure to prevent external pressures being applied directly to it outer surface of the liner, thereby preventing collapse of the liner. In addition, energy conductors, such as electrical wires or optical fibers, can be made integral with the tubular part, and also arranged so as to enhance the desired physical characteristics of the pipe. Energy conductors usually have low tensile strength, and can thus easily be damaged by large deformations such as those exerted by bending. Placing energy conductors inside the inner area ensures that the energy members are not exposed to significant bending stresses.

In the following, the invention will be described in more detail with reference to the drawings, where figure 1 is a schematic cross-sectional view of a composite pipe part containing oppositely positioned internal parts with integrated electrical conductors, figure 2 is a graphic representation showing the reduction in the ratio of tension in the fiber direction with the imposed axial strains as a function of increasing cross-ply angle for a laminate made of high strength graphite fibers, Figure 3 is a schematic cross-sectional view of a composite pipe section showing the internal arrangement of fibers with different angles and electrical conductors, Figures 4, 5 and 6 are schematic cross-sectional views of the internal parts of a composite pipe section, showing alternative internal arrangements of the fibers, Figure 7 is a schematic drawing illustrating the use of a composite pipe section in a wellbore operation, Figure 8 is a schematic cross-sectional view of a composite pipe section showing layers of fiber tape or rope placed in the spaces between about braided layers to define a moment of inertia for bending in the tube part, figure 9 is a schematic cross-sectional view of a composite tube part with longitudinal unidirectional carbon rods lying under braided layers to define a moment of inertia for bending in the tube part, figure 10 is a cross-sectional view of a composite tube having a circular outer diameter profile where the outer composite part consists of longitudinal reinforcement material laid between adjacent layers of fibers, the outer region being bonded to an elliptical inner liner, and Figure 11 is a cross-sectional view of a composite tube having an inner liner with opposed convex surfaces and longitudinal reinforcing members, comprising conductors, located between adjacent laminates forming an outer composite area.

Composite fibers (graphite, Kevlar, fiberglass, boron, etc.) have many advantages, such as high strength, high stiffness, light weight, etc. However, the work response of composite fibers is linear to fracture, and the fibers are therefore not ductile. Spiral-rolled composite pipes must therefore address the tensile limitations in a different way, ie by forming a construction that meets the requirements with a near elastic response, or with large deformations of the matrix. Such a composite device must have a high resistance to bending stresses and internal pressures and external pressures. It must also have high axial stiffness, high tensile and compressive strength, and have resistance to shear stresses. All these properties are combined in the composite tube of the invention to produce a spirally rolled tube which can be bent to a radius compatible with winding on a spool of reasonable size.

P.K. Mallick, in a textbook entitled "Fiber-Reinforced Composites, Materials, Manufacturing and Design" defines composite as follows: "Fiber-reinforced composite materials consist of fibers of high strength and modulus, embedded in or bonded to a matrix with distinct interfaces between them . In general, the fibers are the main load-bearing parts, while the surrounding matrix holds them in the desired location and orientation, acts as a medium for load transfer between them, and protects them from environmental damage due to high temperatures and humidity, for example". This definition defines composites as used in this invention, with fibers selected from a variety of available materials, including carbon, aramid and glass, and a matrix selected from a variety of available materials, including thermoset resins such as epoxy and vinyl ester or thermoplastic resins such as polyether ether ketone (PEEK), polyether ether ketone ketone (PEKK), nylon, etc. Composite structures are capable of carrying a variety of loads in combination or independently, including tension, compression, pressure, bending and torsion.

Webster's "Ninth New Collegiate Dictionary" defines hose as "a flexible tube for conducting fluids". By comparison, a hose is completely different from a composite pipe. Tubing products such as control cables used in subsea applications are constructed of strong fibers such as aramid, dacron or nylon, laid down in a geodesic pattern on a plastic liner substrate of a tubular construction. Alternatively, a hose may be constructed of strong fibers with a low modulus binder material such as rubber. In any case, a hose is designed to carry compressive loads and to exhibit good bending flexibility, but a hose has a very limited ability to carry compression loads, tensile loads and torsional loads or external pressures.

The composite pipe described in this invention can not only carry high internal pressures, but can also carry high compression loads, tensile loads and torsion loads, independently or in combination. Such capability is essential if the tubing is to be used for applications such as coiled tubing in which the tubing is pushed into a high-pressure reservoir and to overcome friction against movement within the wellbore, particularly for highly deviated or horizontal wells. In addition, the pipe must be able to support its own weight when hanging 6,000 meters or more in a wellbore, and must be able to have great traction to pull out tools or to overcome wedging from sand and circulating solids that have collapsed around the pipe. Such loads in the case of spirally rolled pipe in deep wells can be over 10,000 kg. In other applications, the pipe must also be able to carry high torsional loads. It was not considered possible prior to the development represented in the present patent application, that one could design and build a composite pipe which could be bent to a relatively small diameter as required for coiling spiral-rolled pipes, and at the same time be able to bear internal pressures and other loads.

It is also important for the application as coilable spiral-rolled pipe that the liner is integrally attached to the composite structure. The necessity for a banded casing is that under certain operating conditions encountered in boreholes, the outer surface of the pipe will be exposed to higher pressure than the interior of the pipe. In addition, stress and bending of the pipe can introduce microscopic cracks in the laminate that would serve as microscopic pathways for the introduction of external pressure that would be exerted directly on the surface of the liner. If the liner is not bonded to the structure, the outer surface of the liner which cannot withstand high pressures will be subjected to such high external pressures, which in turn would result in collapse of the liner. A non-bonded liner might be able to withstand, for example, external pressures on the order of 690 kPa (100 psi), but would not withstand pressures in excess of 7 MPa, which would typically be imposed in the aforementioned application as spiral-rolled tubing.

The present invention can best be described with reference to the drawings. Figure 1 shows a cross-sectional view of a pipe part which is composed of an outer composite part 2 which can have a generally cylindrical shape, and two inner composite parts 4 which form inner areas inside the tubular part, where an imaginary diametrical line drawn through the inner parts defines a minimum moment of inertia. The cylindrical composite part 2 contains fibers as in crossing layers and oriented with from ±35° to ±70° with the axis of the tube. (±) denotes opposite orientation of the fibers by the indicated number of degrees. This orientation of the fibers is chosen from a range which will provide structural efficiency for the outer generally cylindrical part 2 when this part is subjected to various combinations of loads imposed by bending, stretching, compression, torsion and internal pressures. The outer part 2 may contain from about 5 to about 10% fibers which are oriented at about ±85 to 90°, ie approximately perpendicular to the longitudinal axis of the composite tube part. Inclusion of these peripheral fibers (85-90°) lowers the pipe's Poisson's ratio towards 0.5, and increases the axial stiffness and makes the response to load deformation more linear and thus allows higher axial tensile loads and compression loads. Peripheral fibers may in some applications be unnecessary. These fibers are again embedded in a matrix binder which surrounds the fibers and the layers of fibers into a uniform structure comprising the cylindrical part 2.

The opposed inner composite parts 4, which form the inner regions, contain fibers oriented at 0° with the longitudinal axis of the tube to meet the need for high axial stiffness, and high tensile and compressive strength, are placed close to the axis of least moment of inertia to have only a small effect on the overall bending stiffness of the pipe. One or more energy conductors 5, such as electrical conductors or fiber optic cables, with an optional insulation cover 7, can be centrally located in the inner area 4 so that when the pipe is bent around the axis with the least moment of inertia, there is minimal bending stress on the energy conductors. These conductors may be insulated if necessary, or they may rely on the composite fibers for electrical insulation from each other. Axial loading and thermal expansion can cause cracks in the parts 4, and it may therefore be desirable in these parts to arrange some fibers which are crossed and oriented at ±35° to ±70° with the axis of the tube, to counteract delamination. The cross-layer oriented material which is resistant to shear stress can be arranged either in the form of a woven fabric or braided material, and is usually found in the inner core part 4 in an amount of between 5 and 25%.

The inner areas can be arranged so that the core part 4 has protrusions close to the inner wall of the outer pipe part 2, which protrusions are generally shaped like sinusoidal curves, as shown in figures 1, 3 and 11. In order to reduce the stress in the 0° oriented material during bending of the pipe 2, it is desirable that this material forms the inner areas close to the axis of the smallest moment of inertia for the cross section of the pipe. This is arranged by placing the inner areas so that the 0° material is concentrated in diametrically opposite sides of the tube as in the sine waveform shown, in which the amplitude of the sine curve can be a small projection as in figure 8-11, and up to a larger projection as shown in figures 1 and 3. The projection can be towards the inside of the pipe as shown in figures 1, 2, 10 and 11, thus allowing the outer diameter of the pipe to become circular, or towards the outside of the pipe as shown in figures 8 and 9, so that the inner diameter of the tube 5 can become circular. Good strength in shear and transverse tension in the 0° oriented material in its attachment to the outer generally cylindrical composite part 2 can be achieved by encapsulating the 0° oriented material with ±3° to ±70° cross-ply material, and attaching the cross-ply material to the outer cylindrical composite part.

The fibers in the outer cylindrical part and the inner core parts are held together with a plastic matrix binder material, comprising a thermosetting resin such as vinyl ester or epoxy, or a thermoplastic resin. The outer composite structure consists of several layers of composite material which are braided or filament wound around a thermoplastic tubular lining part 8 so that the lining is integrally attached to the innermost layer or laminate of composite material. The attachment should be integral with the outer composite structure to ensure that it is sufficient to withstand large transverse tensile forces and interlaminar shear stresses, unlike a non-attachment contact. The bonded attachment between the liner 8 and the entire outer composite structure 2 is important to prevent external compressive forces from being exerted directly on the liner, which would collapse the liner.

Economic, structural, damage tolerance and manufacturing considerations may make it advantageous to use fibers of different materials and different resins for the two components of the composite tubular part. The requirements for great stiffness and great strength in the parts in the inner area can, for example, be best met by using 0° graphite fibres. On the other hand, lower costs and higher tensile strength for glass fibers may make glass fibers the material of choice for the outer generally cylindrical part. Other fibers that can also be used are ceramic fibers, polymer fibers, for example from Kevlar fibers which are a product of the Du Pont Company. Test results have also shown when fibers of aramid (Kevlar) are used in the construction of composite coilable pipes, that the pipe becomes very resistant to damage and that final failure modes are localized. For example, damage experienced during burst tests with pipe constructed with aramid fiber reinforcement will most often occur only on one side of the pipe, while the failed pipe shows significant residual tensile strength. Such a characteristic is of considerable value when recovering a failed pipe from the borehole. The mentioned plastic binders, among others, can be used in the production of the components in the composite pipe parts of these materials.

The size of the various components in the composite pipe part will depend on the part's overall size. If the composite pipe part is to be used as a spirally rolled pipe, it will usually have a diameter of from about 12 mm to about 10 cm. A representative composite pipe could have an external diameter of 37.5 mm, a wall thickness of 6.25 mm and a corresponding internal diameter of 25 mm. The structural laminate would be about 4.75 mm thick, and the lining about 1.5 mm thick. Using the design shown in Figure 8, the maximum diameter in the chosen reinforcement area could be 41.6 mm, and the carbon/epoxy selective reinforcement bands would be about 7.5 mm wide.

Reference is again made to Figure 1. It may be desirable to line the interior of the composite tube part with a wear-resistant and chemically resistant lining material 8 to produce a pressure-type chamber. Materials such as polytetrafluoroethylene (PTFE), polyvinyl chloride

(PVC), polyethylene (PE), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), nylon, polypropylene (PP) or polyether ether ketone (PEEK) can be used for this purpose. Co-extrusions of two or more of these materials may also be desirable for certain applications. The seal provided by liner 8 holds fluid within the pipe which may be under internal pressure as high as 70 MPa (10,000 psi) or more. The liner serves as a pressure vessel part to counteract leakage of internal liquid materials, and the outer composite layer forms the structural holder for the liner and thus any internal pressure loads in it.

When used in boreholes, the composite pipe can bulge, and at the bulge points, exert a normal force on the walls of a casing or open hole. This force will create friction as the pipe moves down through the hole. The exterior of the composite pipe can be covered with a protective wear-resistant layer 6 to counteract such wear and friction. Here again such materials as polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polyethylene (PE), ethylene tetrafluoroethylene (ETFE), polyvinylidene fluoride (PVDF), nylon, polypropylene (PP) or polyether ether ketone (PEEK) with or without fiber reinforcement can be used to form this protective layer.

The axial stress in the cross-ply fibers in the outer cylindrical portion of the composite tube due to bending is significantly lower than it would be in similarly placed 0° oriented fibers. Typical reductions in the ratio between the stress in the fibers and the applied axial stress for a cross-ply laminate as a function of the angle of the cross-ply are shown in the graphic representation in Figure 2 using representative properties in a high-strength graphite fiber. It may be noted that for angles greater than about 25°, the fiber stress is less than half the axial stress applied to the laminate, and decreases rapidly for larger cross-ply angles. Orienting the fibers in the outer generally cylindrical portion in the manner described herein optimizes the pipe's ability to carry the applied loads and minimizes stress in the fibers due to bending. Minimizing the bending stresses in the fibers allows larger diameters for the outer generally cylindrical portion of the composite pipe than would otherwise be possible for a specific coil size. On the other hand, a tube of a given diameter, produced in this way, can be wound on a coil of smaller diameter. The generally cylindrical shape of the composite pipe is also well suited for introducing such a part into the well with the chain drive mechanism that is normally used to drive the pipes into the wellbore. The design of the composite pipe according to the invention, where internal areas are formed on opposite side walls, creates a largest and a smallest moment of inertia and forces a desired bending direction. The effect of this is that it forces the composite tubes to wind onto a coil by bending around the minimum moment of inertia. Down the borehole, the crack pattern or bulge pattern will be a mixed mode that has a period associated with the smallest moment of inertia and a longer mode with less curvature associated with the largest moment of inertia. Another advantage of forcing the bend to always occur around the same axis is that damage that may occur during the bend is isolated and localized to a particular area of the pipe, instead of being globally distributed around the pipe. The absence of global damage accumulation will lead to a longer life of the pipe. The advantage of the selective reinforcement design is that materials of greater stiffness and greater strength can be placed in the inner regions of the composite pipe without causing a significant increase in the bending stresses or sacrificing a smaller bend radius allowed for coiling.

In figures 3, 4, 5 and 6, the broken lines inside the body of the tubes indicate the orientation of the fibers in the layers of the tube. The dotted lines indicate the fibers which are oriented approximately parallel (0°) to the axis of the tube. Lines consisting of alternating dots and dashes indicate fibers oriented approximately ±35° to ±70° with the axis of the tube. Lines consisting of many dashes separated by two short dashes indicate fibers oriented approximately ±35° to ±70° with the axis of the tube. Finally, a line consisting of bare lines indicates fibers oriented at about 90° to the axis of the tube. Figure 3 illustrates the internal arrangement of fibers for a composite tube of the type shown in Figure 1. In Figure 3, the angulation of the different fibers in the composite tube part is represented by individual lines. Each line represents a layer or laminate of fibers 14. The reference number 16 denotes the outer wear cover, and 18 the inner wear and chemical resistant liner for the composite pipe. As shown in the drawing, the inner composite layer is made of 0° oriented material and cross layer material. The cross-ply fibers are usually held in a woven fabric or in braided form as shown, and may be extended from the inner regions to connect with the outer generally cylindrical portion of the composite tube. For structural continuity and sealing, at least a portion of the cross-ply material in the inner regions is still around the inner region of the outer, generally cylindrical portion. The 0° oriented fibers can also be arranged in the form of a cloth or fabric, but this material is however usually present as bundles of fibers or ribbons. As previously noted, the outer cylindrical portion contains the layers 14 of primarily ±35° to ±70° cross-ply fibers with or without a small amount of fibers oriented ±85° to ±95°. The fibers in the composite pipe section are encased in a suitable plastic bonding material (not shown in the drawing) to form a unitary structure which in turn is bonded to the liner 18.

Figures 4, 5 and 6 show different internal arrangements of fibers in the inner areas. The electrical conductors 5 are not shown for simplicity, but would be placed within a plane along the least moment of inertia of the composite pipe, as shown in Figure 3, with the fibers gradually formed around the conductors. In Figure 4, the 0° oriented and the cross-lag oriented fibers are both shown in a generally elliptical shape. In Figure 5, there are 0° oriented fibers represented by dots, concentrated in the inner part of the core region. In Figure 6, both the 0° oriented fibers and cross-ply oriented fibers are arranged in a linear form which is parallel to the axis of minimum moment of inertia for the pipe part. In each of the devices shown in Figures 4, 5 and 6, both the sine wave regions and the base portion of the inner region core members are surrounded by cross-ply oriented fibers which continue completely around the inner regions and onto the inner surface of the outer generally cylindrical composite member to resist shear stresses and delamination.

The cross-ply fibers used in the inner areas of the composite part have the preferred orientation, but it is however within the scope of the invention to use fibers oriented from ±35° to ±70° in the inner areas to encapsulate the axial or 0° inner parts. Additionally, while ±45° oriented fibers are preferred for use in the outer generally cylindrical composite portion for some construction needs, fibers oriented from ±35° to ±70° may be used without departing from the scope of the invention. The fiber sequence or stacking frequency for ±45°, 0°, 90° and ±45° fiber orientations as shown in the drawings are representative only, and may be varied to meet specific construction needs.

The axially oriented material is necessary for high axial strength and stiffness in a pipe which is otherwise tailored to show high pressure bearing capacity and low bending stiffness. For coiling purposes, a tube constructed in this way will bend about the axis of minimum moment of inertia without exceeding the allowable low stress characteristics of uniaxial material (compared to the high axial stresses allowed for the layers of cross-ply laminate 14 (Figure 3) that make up the body of the tube ), and still be sufficiently flexible to allow bending of the device on a coil. In such a form, the pipe is made essentially circular on the inside, with the unidirectional material integrated into the side wall, so that an irregularity is created on the outside of the pipe instead of on the inside. Such unidirectional materials can be arranged in the form of circular rods (figure 9) placed between the cross-laid layers that make up the body of the pipe. The rods can also be shaped to adapt to the natural geometry that develops when the rods are inserted. Alternatively, unidirectional tape or twine (figure 8) can be placed between the cross layers in the pipe. For a braided construction, the unidirectional material can be introduced as warp material as an integral part of the layers in the braid.

Alternative designs of the invention shall be described in the following with reference to Figures 8-11 in the drawings. Figures 8 and 9 show an arrangement of an alternative spirally rolled pipe construction in which the selective structural reinforcement parts form an irregularity on the outer areas on opposite side walls of the outer cylindrical part 2. Figures 10 and 11 give a generally circular design on the outside of the pipe, with a non-circular protrusion on the inside of the tube, to allow for the selective reinforcements, and both types of design offer the advantage of a minimum moment of inertia for bending in the composite tube. In Figure 8, the composite pipe consists of an inner thermoplastic lining 3 to form a body on which the tubular part can be constructed, and to provide a relatively smooth internal bore in the pipe part. The lining serves the function of sealing against leakage of internal fluids under pressure. These pressures can be as high as 70 MPa (10,000 psi). The layers of braided or filament wound materials such as Kevlar 49 and carbon, encapsulated in a matrix material such as epoxy, are applied as the outer generally cylindrical portion 2 of the pipe. A pair of oppositely placed inner areas 4 are formed in the outer generally cylindrical part by placing layered strips 11 of carbon or other material of high rigidity in a unidirectional fiber tape or the like between adjacent concentric layers 9 of braided carbon/epoxy or filament wound material. In the case of the cylindrical part 2, the layered strips 11 are also encapsulated in a matrix material such as epoxy. The strips of carbon/epoxy tape 11, e.g. 7.5 mm wide, can be placed between e.g. five of the braided layers 9 which form the generally cylindrical outer part 2. These tape strips 11 can be made of e.g. five layers of 0.125 mm thick fiber tape which would then make each layer 11 about 0.625 mm thick. This arrangement of strip strips constituting the internal areas 4 on opposite sides of the pipe section is sufficient to define a minimum moment of inertia for bending, which extends diametrically through the internal areas, and a maximum moment of inertia for bending which is generally orthogonal to the minimum moment of inertia . These inner parts or strips 11 which make up the inner areas are designed together with the other structural elements in the pipe part to give great axial stiffness and strength to the outer part of the pipe part, so that the pipe has greater bending stiffness around the largest axis compared to the bending stiffness around the smallest axis, to form a preferred bending direction around the axis with minimum bending stiffness when the pipe is coiled or uncoiled.

A further advantage of forcing the tube to bend around a single axis is associated with the accumulation of damage and wear that will naturally occur during thousands of trips on and off the coil. Repeated deployment with high internal pressures and high axial tensile and compression loads will eventually lead to damage to the pipe, and the need to replace it or reduce the allowable loads. If the pipe is free to bend in any direction, the damage will be universal around the circumference of the pipe, while if the damage is preferential as will happen with selective reinforcements so that the bending is forced to occur around the smallest moment of inertia, the damage will be localized and lead to a longer lifetime for the pipe.

Reference is now made to Figure 9, where the inner areas are provided with an alternative arrangement by arranging a plurality of high modulus fiber rods between adjacent braided or filament wound layers 9. Such rods consist of carbon, boron, glass etc. encapsulated in a matrix material such as epoxy or a thermoplastic material such as PEEK. These rods are shown positioned between the fourth and fifth braided or filament wound carbon or aramid layers 9. More than one set of rods may be positioned between other intersecting layers. The rods 13 can be of the order of 1.7 mm in diameter. A void 17 formed between the fourth and fifth layers by the separation action of the rods can be filled by a filler material 15 such as unidirectional carbon or E-glass yarns or fibers encapsulated in a matrix in the area near the outer rods of the system. It is important that the rods remain straight and in a fixed radial position in the outer, generally cylindrical part. This is to ensure that the smallest moment of inertia for bending will still be defined at the inner area of the structure, which includes the rods 13 and the filling material 15 in the embodiment in Figure 9.

The devices shown in Figures 8 and 9 form an irregularity 4 on the outer surface of the outer cylindrical part 2 so that the axial elements 11 and 13 for selective reinforcement can be inserted into the side walls and still provide a liner 3 having a circular internal drilling out. Certain operations down the borehole require approximately circular internal borings in a pipe string, for example to facilitate the pumping of tools through the pipe string. An example is the use of ball packings used to seal perforations in the casing in various well treatment operations. Pumping tools and plugs that require differential pressure across a device also require a smooth circular tube for application and operation. A circular internal bore in the pipe string may thus also be necessary in some applications.

The inner areas 4 of all designs can consist of energy conductors (not shown in figures 8-10) similar to the design of the pipe parts in figures 1, 3 and 11. These energy conductors can be electrical or optical conductors or any material or substance which can be modulated with information data. These energy conducting paths can also serve as part of the physical construction of the internal areas that form the smallest moment of inertia for bending inside the tube. Of primary importance when placing the conductors in these inner areas is to ensure that the bending stresses are minimal. When placed in the area of selective reinforcement, the conductors are close to the neutral bending axis. If they are placed elsewhere in the pipe, the bending stresses may exceed those permitted and result in breakage of the conductors. This would be even more critical if the conductors were optical fibers.

Placing the conductors in the area of selective reinforcement will also produce additional stiffness. A metal conductor as shown in figure 21 on figure 11 will for example form a unidirectional longitudinal stiffening material in the opposite side walls, which will provide axial stiffness together with compression strength as well as tensile strength and shear strength. This reinforcement will help to unfold the coiled tube to push it into a tube or the like, to pull it out of a tube or hole, and will help to create a maximum and minimum moment of inertia to promote preferential bending of the coiled pipe, and at the same time form a structure that will not collapse, thus maintaining a general circular outer shape necessary to feed the pipe through a pressure-loaded stripping element at the entrance to the well.

Reference is now made to figures 10 and 11, where the outer composite layers 9 consist of fibers wound or braided in a desired orientation, and the tape on an inner liner 3. The fibers that make up the layers 9 are embedded in a matrix that keeps them oriented and acts as a load transfer between the fibres. These fiber layers are tightly bonded to each other and to the liner 3 so that external pressure cannot be transmitted from outside the pipe through cracks or spaces in the outer composite layer and directly to the outer surface of the liner 3, thereby causing the liner to collapse. The arrangement of the materials in Figures 10 and 11 is such that the outer surface of the composite pipe is approximately circular despite longitudinal reinforcement parts in opposite side walls of the pipe. While in Figures 8 and 9 the insertion of the reinforcement layers 11 has created an additional bulge in the side walls of the tube, the design in Figures 10 and 11 is provided with shaped liners, which form a built-in inner bulge in the side walls to form a space for the parts 11. In Figure 10, the lining 3 is somewhat elliptical with oppositely positioned, relatively straight inner side wall parts 10 located close to the longitudinal reinforcement parts 11. This shape gives a somewhat greater wall thickness in these opposite side walls 10, which in turn provides the additional space necessary to allow room for the longitudinal or unidirectional materials 11 which constitute the reinforcement in opposite side walls, and at the same time maintain a generally circular outer shape of the cylindrical part 2.

In Figure 11, the inner liner is shaped to form a concave inner wall 25 which also provides a thicker wall area in the outer composite portion near the opposite inner walls 25 to accommodate the additional thickness caused by the build-up of the aligning or stiffening materials 11 which is placed between the layers 9.

Conventional stripper elements used in spiral-rolled pipe operations to seal over the wellbore entrance have a circular cross-sectional profile. To allow for the non-circular cross-sections shown in Figures 8 and 9, the inner diameter of the stripper elements must be made to a similar design. In the alternative design of the spiral-rolled composite pipe as shown in figures 10 and 11, the pipe's construction is such that it has a circular outer diameter profile, and thus can use a conventional stripping element for spiral-rolled pipes. Insertion of selective reinforcement 11 as shown in figures 3, 10 and 11 in a design with a circular outer diameter makes it necessary to arrange the non-circular cross-section of the inner lining of the pipe, and thus make the opposite side walls thicker. This thicker cross section is necessary to allow for the axially oriented 0° carbon/epoxy material or other high stiffness fiber/matrix reinforcement material 11, which forms an axis with minimum moment of inertia so that bending will naturally take place around a preferred axis.

The embodiment in figure 11 is a variation of that shown in figure 10, in that the liner 3 takes an approximate shape of a figure eight. This design also provides sufficient room in the sidewalls to accommodate the additional axially oriented 0° carbon/epoxy materials or other fiber/matrix material with high stiffness. Such a configuration is necessary when very high axial tensile loads and compression loads are required, such as for deploying a pipe in very deep wells. The polymer liner 3 can be extruded in the design shown in figure 10 or 11, and later used as a foundation for the construction of the outer composite wall 2. It is important for coiled pipes and other applications that exert external compressive loads that the liner is integrally bonded to the outer structural element to form a uniform structure and thus prevent external pressure from being directly applied to the outer surface of the lining 3.

Reference is now made to Figure 7, which shows a wellbore, generally designated by reference numeral 19. The wellbore has a vertical upper portion 26 extending to the surface, a vertical lower portion 28 and a diverging portion 30 connecting the upper and lower portions 26 and 28. The vertical portion 26 and the deviated portion 30 are normally several thousand feet long, while the vertical portion 28 is usually much shorter. The wellbore may also end in a near horizontal section.

In operable relation with the wellbore 19 and placed on the surface, there is arranged an injector unit denoted by the reference number 24. A reel 20 is also arranged on the surface, and the composite pipe 22 is stored on this reel. Roller bellows are often used as guides in the injector 24, and also to drive the composite pipe down the hole. Contacts, not shown, are arranged on the reel 20 to form electrical or optical connections between the wires in the pipe 22 and a surface cable 36, so as to connect the wires 5, 21 in the pipe 22 in the borehole with a control system 38 on the surface.

Coil 20 and injector 24 are not detailed, since these types of devices are well known in the art. Specific coil and injector devices are shown in US 3,401,794, US 3,722,594 and US 4,682,657, among others.

After the apparatus as shown in figure 7 is assembled, the composite part 22 is passed through the injector 24. The desired well tool, such as a logging tool 32, is then attached to the pipe 22. An electrical connection is made between the well tool and the conductors 5, 21 which are integrated in the pipe 22. The well tool 32 is then placed in the upper part 26 of the well 18 and lowered into the well using gravity. When the well tool 32 reaches the deviated part 30 in the well, the frictional contact between the tool and the wall of the deviated part is sufficiently large to overcome the force of gravity. When this occurs, the injector 24 is used to apply a downward force to the composite pipe so that the logging tool 32 is forced into and along the deviated section 30.1 In the event that the continuous application of force by the injector 24 is not sufficient for this purpose, the injector may be operated as follows that it provides alternating upward and downward movement of the composite pipe and the logging tool 32 to ensure continuous downward progress. Activation of the logging tool at desired intervals is carried out by the control device 38 on the surface through the wires 5, 21 which are placed inside the composite pipe, and electrically or optically connected to the logging tool 32.

When the logging tool 32 leaves the deviated part of the well and enters the vertical area 28, further obstacles to movement of the tool may arise. In this case, the described procedure can be repeated to produce further downward movement of the logging tool. It has been seen that large compression forces can be applied to a coiled pipe used down a borehole. The axial bracing that is arranged is thus very important, which complicates the structural requirements for a coilable pipe. Combination of axial stiffness and low bending stiffness has led to the unique development presented in this invention.

If another type of well tool is used instead of the logging tool 32 (e.g. a perforating tool) the device is connected and moved to the correct operating zone or formation in the well hole 19 in the manner previously described. After it reaches the desired zone, appropriate switches in the control device 38 can be operated to start the perforating tool by means of electrical circuits formed by conductors 5 (figures 1 and 3) and conductors 21 (figure 11) which are placed inside the composite pipe. Composite pipes that have integrated electrical conductors also offer a significant advantage over previous spiral-rolled pipe operations. Placing the conductors in the wall of the tubular cable leaves a completely open bore in the pipe, which will allow the use of the pipe as a completely open fluid conductor to perform downhole operations. Fluids and/or other devices can be pumped through the tubing to treat downhole formations, operate a mud motor for drilling or coring, or to design a variety of tests and operations with instruments and tools. These suggested areas of use are not intended to be limiting in this context. At the same time, placing the conductors in opposite side walls will provide an axial stiffness that also promotes preferential bending, which helps to provide a low bending stiffness.

In addition to its use in well logging and well overhaul, the composite pipe according to the invention can be used in underwater hydraulic lines or as production pipe in which long sections of pipe are coiled and led down the borehole for permanent production. Production tubing is normally larger in diameter than is necessary for spiral-rolled tubing, and may be too large to bend on a spool of practical diameter. If the pipe diameters become too large for coiling, it is possible to manufacture the composite pipe on site, on land or at sea. Large coil sizes are practical for use offshore where the composite pipes can be manufactured close to a dock site. The presence of electrical or optical energy conductors in the pipe enables the operation of many downhole tools, as well as data collection from downhole or other remote locations.

The obvious importance of the winding characteristics of such a spirally wound tube is central to this invention. It has been found that with the correct materials, orientation and arrangement thereof, a pipe or cable can be constructed which is capable of being subjected to high stresses arising from coiling and uncoiling and from loads imposed in the borehole environment. In the special well operations in the petroleum industry on land, it is necessary to limit the size of the coils due to the transport needs for handling such coils. A coil with a diameter of 2.4 meters and a pipe with a diameter of 5 cm will result in significant stresses due to the coiling operation. The arrangement of the pipe structure described in this application is a response to the needs resulting from this representative coiling situation.

Another advantage can be noted for the use of composite pipe fittings. With composite pipes, deformations become more elastic and usually greater than for steel pipes, and this stored energy can be used constructively to help release the pipe from a wedged position or a friction bond. The pressure in the tube can be pulsed to produce the intended function. Although this technique can also be used for spirally rolled steel tubes as well as for composite tubes, the high stiffness of steel compared to the low stiffness of the tube according to the invention will limit the amount of local displacements associated with pressure pulsing of steel tubes compared to displacements obtained using composite tubes . Activation of a downhole gasket will allow pressure pulsing of the composite pipe with lower pressure applied to the inside and outside of the pipe. Pressure pulsing can also help free a composite pipe that is wedged down the borehole.

When designing composite structures, one can use several well-known techniques such as braiding, pulling, filament winding and casting. To create the multiple layers characteristic of the invention, a number of individual braids or filament winding devices are arranged in a row, with each composite lamina layer placed directly over the previous lamina layer to build up the total thickness required, with resin material applied to each layers to ensure total wetting between the fibers and between the layers. This wetting produces the final uniform structure necessary to prevent pressure migration from the outer surface of liner 3 (Figures 8-11) and liner 8 or 18 in Figures 1 and 3.1 drawing filaments or fibers are drawn through a resin -impregnation device, and then through nozzles to give it the desired shape, or alternatively resin can be injected inside the nozzles. Finally, the desired product, which is produced continuously, can be wound on a reel or spool. As an example, drawing is used in US 4,416,329 to produce a tape structure containing bundles of graphite fibers saturated with thermoplastic resin. The surfaces of the belt are covered with layers of woven material, such as glass cloth. Corners on the tape are made of Kevlar or glass. US 4,452,314 used drawing to form curved sections consisting of glass filaments or other reinforcing materials placed in a thermosetting resin. The curved sections combine to form a suction rod.

The composite pipe part according to this invention can also be produced using drawing processes comprising either conventional drawing equipment or drawing winding equipment or drawing in combination with braiding or filament winding. In one method, the 0° oriented material is drawn in advance and fed into a similarly designed depression on a drawing die, and later drawn together with the cross-layer material. Drawing can also be used to make either continuous or discrete lengths of composite pipe parts. In the draft winding process, the 0° oriented material is either fed into the process as a prefab bar or fed into the unit as a prefab strip or wet lay. The cross-lamination material is then wound onto the tube and the assembly is drawn through a die for integral curing. The drawing process can use material produced by weaving or braiding the fibres. The woven or braided material can be prefabricated as a feed material, or can be fabricated in the production line as part of the drawing operation.

Claims (13)

1. Composite tubing (22) for storage on a spool (20), which can be coiled and uncoiled for use in a wellbore (19), comprising a generally cylindrical tubular casing (3) having a smooth internal bore and high axial stiffness , an outer composite part (2) which is integrally bonded with the liner, where the outer composite part (2) contains fibers which are cross-laid in concentric layers (9) around the liner and baked in a plastic binding material which penetrates the entire outer composite part so that the liner ( 3) and the outer composite part (2) maintains a generally cylindrical shape during use and during winding on a reel (20), and axial stiffness elements (11,13) which are arranged in opposite side walls of the outer composite part (2) to create a minimum moment of inertia on the cross-section to form a preferred bending direction of the tube and thus exert minimal bending stresses on the axial stiffness elements. 2. Composite pipe (22) according to claim 2, where the outer composite part has sufficient structural integrity in the layers (9) of fibers and surrounding binding material to essentially prevent the migration of fluids under pressure into contact with the outer surface of the lining (3 ), and in that the binding of the liner (3) to the outer composite part (2) is sufficient to prevent the migration of fluids under pressure along the outer surface of the liner (3). 3. Composite pipe (22) according to claim 1 or 2, wherein the plastic binder material has a modulus of elasticity greater than 689 MPa (100,000 psi) to provide sufficient support and load transfer characteristics to prevent the pipe from collapsing when coiled or loaded with high external pressure or when subjected to high axial tensile and compressive loads. 4. Composite pipe (22) according to claim 1, 2, or 3, where the outer composite part (2) comprises several layers (9) of continuous fibers oriented at ±35° to ±70° with the longitudinal axis of the tube. 5. Composite pipe (22) according to any preceding claim, where the axial stiffness elements (11,13) are arranged by structural rods (13) which are oriented substantially at 0° with the longitudinal axis of the pipe. 6. Composite pipe (22) according to any preceding claim, where the outer composite part (2) consists of continuous fibers embedded in a plastic binder matrix, which is wound, braided or woven in concentric layers (9) on the lining. 7. Composite pipe (22) according to any preceding claim, where it has peripherally oriented fibers approximately perpendicular to the longitudinal axis of the pipe. 8. Composite pipe (22) according to any preceding claim, where the axial stiffness elements comprise at least one energy guideway (21). 9. Composite pipe (22) according to any preceding claim, wherein the liner (3) is preformed with a concave surface on opposite side walls, and a generally cylindrical outer surface to provide sufficient thickness in the side walls to accommodate the axial stiffness elements (11, 13), and still maintain a substantially cylindrical outer surface of the composite tube (22). 10. Composite pipe (22) according to any preceding claim, where the axial stiffness elements (11,13) comprise a unidirectional material which is inserted between concentric layers of woven or braided material as an axial warp part. 11. Composite pipe (22) according to any preceding claim, where the inner parts comprise narrow strips (11) of material which are placed along the longitudinal axis of the pipe and encapsulated in a matrix of material with a modulus of elasticity greater than 7000 kg/cm<2> . 12. Composite pipe (22) according to any preceding claim, where the liner (3) has a circular bore, and the axial stiffness elements (11,13) are arranged in the outer composite part (2) so that a displacement in the side walls of the outer composite part ( 2) due to axial stiffness elements (11) is transferred to the outer surface of the spiral tube in the form of an irregularity on the outer surface. 13. Composite pipe (22) for coiling in an open tubular shape on a reel (20) and for being uncoiled for injection under power into a wellbore (19) or the like, where an outer composite part (2) containing a plurality of continuous fiber layers (9 ) which is applied to a pressure-resistant inner tubular liner member (3) and cross-laminated to resist internal and external pressures and tensile and compressive loads while maintaining a low bending stiffness, a matrix of plastic binder material with a modulus of elasticity greater than 689 MPa (100,000 psi ) which surrounds the fibers and fiber layers so that the fibers are baked into the matrix, and binding the fiber layers to each other and to the liner to form an integrated structure with the liner (3), which prevents fluids under external pressure from having direct access to the outer surface of the liner (3), and axial internal reinforcement parts (11,13) arranged inside the outer composite part (2) in opposite side walls thereof, to form a preferred bending axis when the tube (22) is wound in open tube form on a reel (20).