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History of coiled tubing technology

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Numerous continuous-length tubular service concept trials and inventions paved the way for the creation of present day coiled tubing (CT) technology. The following discussion outlines some of the inventions and major milestones that directly contributed to the evolution of the continuous-length tubular products used in modern CT services.

Birth of coiled-tubing technology

The origins of continuous-length, steel-tubing technology can be traced to engineering and fabrication work pioneered by Allied engineering teams during the Second World War. Project 99, code named "PLUTO" (an acronym for Pipe Lines Under The Ocean), was a top-secret Allied invasion enterprise involving the deployment of pipelines from the coast of England to several points along the coast of France. The 3-in. inside diameter (ID) continuous-length pipelines were wound upon massive hollow conundrums, which were used to spool up the entire length of individual pipeline segments. The reported dimensions of the conundrums were 60 ft in width (flange-to-flange), a core diameter of 40 ft, and a flange diameter of 80 ft. These conundrums were designed to be sufficiently buoyant with a full spool of pipeline to enable deployment when towed behind cable-laying ships. Six of the 17 pipelines deployed across the English Channel were constructed of 3-in.-ID steel pipe (0.212-in. wall thickness). The 3-in.-ID steel pipelines, described as "Hamel Pipe," were fabricated by butt-welding 40-ft lengths of pipe into approximately 4,000-ft segments of pipeline. These 4,000-ft segments were then butt-welded together and spooled onto the conundrums. A total of 172,000,000 gallons of petrol was reported to have been delivered to the allied armies through PLUTO pipelines at a rate of more than 1 million gal/D.[1]

Although the initial development effort of spoolable steel tubulars was reported to have occurred in the early 1940s, the first concept developed for use of continuous-length tubing in oil/gas wellbore services can be found in U.S. Patent 1,965,563, "Well Boring Machine," awarded on 10 July 1934 to Clyde E. Bannister.[2] This approach utilized "reelable drillpipe," which was flexible enough to be coiled within a basket for storage when it was run into or out of the borehole (Fig. 1). This original concept used a rubber hose as the drillpipe, with the hose couplings designed to accommodate the attachment of two steel cables to provide the axial load support for the weight of the hose and bottomhole drilling assembly. The hose-coupling-cable-attachment clamps were also designed to allow removal of the steel cables as the flexible drillstring was removed from the wellbore. When pulling the flexible drillstring out of the wellbore, the separate cable lines were spooled onto drums for storage.

The reeled drillstring system repeatedly used a bottomhole mud percussor and an oscillator (at different times) to drive the bit. In 1935, a total of 4,000 ft of borehole was drilled with this system, with a maximum single borehole depth of 2,000 ft.[3] The Bannister reelable drillpipe system reportedly became inactive in or about 1940 because of the lack of suitable downhole motors available.

The first concept on record for use of continuous-length steel tubing in well-service work was proposed by George D. Priestman and Gerald Priestman, as seen in U.S. Patent 2,548,616, "Well Drilling," awarded 10 April 1951.[4] The patent claimed the invention of a reeled, rigid-pipe drilling system in which the steel pipe is spooled onto a carrier reel. The reeled drillpipe was proposed to be deployed into the wellbore through a series of rollers mounted above the carrier reel, which was also fashioned to serve as a pipe bender (Fig. 2). Once the steel pipe was run through the pipe-bending device, the pipe was oriented vertically and entered a pipe straightener mounted on the wellhead. This straightener was proposed as a series of motor-powered rollers and also served as the drive mechanism for deploying and retrieving the drillpipe.

Modern CT technology

The chronology of modern-day steel CT technology development appears to begin in the early 1950s with U.S. Patent 2,567,009, “Equipment for Inserting Small Flexible Tubing into High Pressure Wells,” awarded to George H. Calhoun and Herbert Allen on 4 September 1951. The fundamental concepts developed and claimed by Calhoun and Allen[5] served as the basis for the vertical, counter-rotating chain tractor device, which was upscaled to serve as the design for the first CT injector placed in operation.

This apparatus provided the ability to insert, suspend, and extract strings of elongated cylindrical elements (such as tubing) for well-intervention services with surface pressure present. A modified version of this device was originally developed to enable submarine vessels to deploy a radio communications antenna up to the ocean surface while still submerged. Using the Calhoun and Allen concept, Bowen Tools developed a vertical, counter-rotating chain tractor device called the “A/N Bra-18 Antenna Transfer System,” which was designed to deploy a ⅝-in. outside diameter (OD) polyethylene encapsulated brass antenna from as deep as 600 ft beneath the water level. Fabric-reinforced phenolic “saddle blocks” grooved to match the OD of the tube were installed as the middle section of the drive chain sets, securing the antenna during operations. The antenna was stored on a carrier reel located beneath the antenna transfer system for ease of deployment and retrieval. The pressure seal was provided by a stripper-type element, which allowed the antenna to penetrate the hull of the vessel. The basic principles of this design concept aided in the development of the prototype Bowen Tools CT injector system.

In 1962, the California Oil Co. and Bowen Tools developed the first working prototype “continuous-string light workover unit” for use in washing out sand bridges in U.S. Gulf of Mexico oil/gas wells (Fig. 3). The original “Unit No. 1” injector was designed as a vertical, counter-rotating, chaindrive system built to run a string of 1.315-in.-OD tubing and operate with surface loads of up to 30,000 lbf. The core diameter of the tubing reel was 9 ft, and was equipped with a rotating swivel mounted on the reel axle to allow continuous pumping down the tubing throughout the workover operation.

The first full-scale continuous length of CT was fabricated from highly ductile 40-ksi-yield, low-alloy Columbium steel. This low-alloy Columbium “skelp” was reportedly rolled to a thickness of 0.125 in. by the Great Lakes Steel Co. (Detroit, Michigan) and then milled into 1.315-in.-OD tubing by Standard Tube Co. (Detroit, Michigan). The 50-ft milled tube lengths were butt-welded together using a combination tungsten inert gas (TIG) and metal inert gas (MIG) process. The assembled tubing string was spooled onto a reel with a 9-ft core diameter to a total length of 15,000 ft and then subjected to numerous bending and loading cycles. The performance of this tubing string and CT unit was tested in several wells (located inland and offshore of south Louisiana) in the early to mid-1960s. The services performed by this original CT unit included sand washing and fishing a storm choke out of the existing completion tubing.[6]


  1. Hartley, A.C. 1948. Operation Pluto. In The Civil Engineer in War, 3, 201-210. London: Institution of Civil Engineers.
  2. Bannister, C.E. 1934. Well Boring Machine. United States Patent No. 1,965,563.
  3. Ledgerwood Jr., L.W. 1960. Efforts to Develop Improved Oilwell Drilling Methods. J Pet Technol 12 (4): 61-74.
  4. 4.0 4.1 Priestman, G.D. et al. 1951. Well Drilling. United States Patent No. 2,548,616.
  5. Calhoun, G.H. and Herbert, A. 1951. Equipment for Inserting Small Flexible Tubing into High-Pressure Wells. Patent No. 2,567,009.
  6. Slator, D.T. and Hanson Jr., W.E. 1965. Continuous-String Light Workover Unit. J Pet Technol 17 (1): 39-44. SPE-938-PA.

Noteworthy papers in OnePetro

Loughlin, Michael J., Plante, Mark 1998. History of and Applications for a Coil-Tubing-Conveyed, Inflatable, Selective Injection Straddle Packer, European Petroleum Conference, 20-22 October. 50655-MS.

Blount, C.G., Ward, S.L. et al. 1993. Emerging Coiled-Tubing Applications at Prudhoe Bay, Alaska, SPE Western Regional Meeting, 26-28 May. 26086-MS.

External links

See also