Spoolable composite tubular member with energy conductors

#Coiled steel tubing finds a number of uses in oil well operations. For example, it is used in running wireline cable down hole with well tools, such as logging tools and perforating tools. Such tubing is also used in the workover of wells, to deliver various chemicals downhole and perform other functions.

#Steel coiled tubing is capable of being spooled because the steel used in the product exhibits high ductility (i.e. the ability to plastically deform without failure). The spooling operation is commonly conducted while the tube is under high internal pressure which introduces combined load effects. Unfortunately, repeated spooling and use causes fatigue damage and the steel coiled tubing can suddenly fracture and fail. The hazards of the operation and the risk to personal and the high economic cost of failure in down time to conduct fishing operations forces the product to be retired before any expected failure after a relatively few number of trips into a well. The cross section of steel tubing expands during repeated use resulting in reduced wall thickness and higher bending strains with associated reduction in the pressure carrying capability. Steel coiled tubing is limited as to internal pressures up to about 5000 psi. Higher pressures significantly reduce the integrity of the tubing so that it will not sustain continuous flexing and thus severely limit its life, even to a single field application.

#It is therefore desirable to provide a non-steel coil tubing which is capable of being deployed and spooled under borehole conditions, which does not suffer from the limitations of steel tubing and is highly resistant to chemicals.

#FIG. 1 is a schematic cross-sectional view of a composite tubular member containing oppositely disposed inner members with integral electrical conductors.

#FIG. 2 is a graph showing reductions in the ratio of the strain in the fiber direction to the imposed axial strain as a function of increasing the cross-ply angle for a laminate made of high strength graphite fiber.

#FIG. 3 is a schematic cross-sectional view of a composite tubular member showing the internal arrangement of fibers of differing angularities and electrical conductors.

#Composite fibers (graphite, Kevlar, fiberglass, boron, etc.) have numerous assets including high strength, high stiffness, light-weight, etc., however, the stress strain response of composite fibers is linear to failure and therefore non ductile. Composite coiled tubing must therefore address the strain limitations in another manner, i.e., by providing a construction to meet the requirements with a near elastic response or with large deformations of the matrix. Such a composite arrangement must have high resistance to bending stresses and internal pressure and external pressure. It must also have high axial stiffness, high tensile and compressive strength and be resistant to shear stress. All of these properties are combined in the composite tubular member of the invention to provide a coiled tubing which can be bent to a radius compatible with winding onto a reasonable size spool.

#P. K. Mallick in the text book entitled Fiber-Reinforced Composites, Materials, Manufacturing and Design, defines a composite in the following manner: "Fiber-reinforced composite materials consist of fibers of high strength and modulus embedded in or bonded to a matrix with distinct interfaces (boundary) between them. In general, fibers are the principal load-carrying member, while the surrounding matrix keeps them in the desired location and orientation, acts as a load transfer medium between them, and protects them from environmental damages due to elevated temperatures and humidity, for example". This definition defines composites as used in this invention with the fibers selected from a variety of available materials including carbon, aramid, and glass and the matrix or resin selected from a variety of available materials including thermoset resin such as epoxy and vinyl ester or thermoplastic resins such as polyetheretherketone (PEEK), polyetherketoneketone (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 conveying fluids". By comparison, a hose is distinctly different from a composite tube. Hose products such as umbilical lines used in subsea application are constructed of high strength fibers such as aramid, dacron, or nylon laid down in a geodesic patter onto a substrate plastic liner tubular structure. Alternatively, a hose may be constructed of high strength fibers with a low modulus binder such as rubber. In either case, a hose is designed to carry pressure loads and to exhibit good bending flexibility, but a hose has very limited ability to carry compressive, tension and torsion loads or external pressure.