Coiled Tubing and Coil Pipe Assemblies

Coiled Tubing and Coil Pipe Assemblies

The use of coiled tubing as a means of conveying fluid under pressure is advantageous for a number of different applications. These include fluid control systems, HVAC, fire protection, and other piping system components.

A coil pipe assembly may comprise a flexible first tubing member and a flexible second tubing member each extending axially from a forward distal end to a rearward distal end. A unitary sheathing member commonly surrounds the first and second tubing members to define a generally expandable, self-retracting coil portion for each of the tubing members.

Coiled Tubing

Coiled Tubing is used in the oil and gas industry to carry out various well intervention and drilling applications. It is a continuous length of tubing that is inserted into a well from a reel at the surface and then withdrawn from the well later on. The tubing is typically used to inject fluids into the well for stimulation of production, to remove unwanted material from the well, or for cleaning operations.

CT assemblies include the injector head, coiled tubing reel, control cabin, power pack, and well control equipment. The injector head provides the drive force to push and pull the coil in and out of the well bore. The control cabin monitors and controls the coiled tubing and the power pack generates hydraulic and pneumatic power to operate the CT unit.

The Injector Head uses triplex chains to grip the coiled tubing between profiled gripper blocks that are sized for the tubing diameter. The motors drive the chains and hydraulic tensioning mechanisms keep correct chain tension to prevent the coiled tubing from being crushed or slippage.

Most coiled tubing strings are monowall but some string designs have tapered walls that change thickness from top to bottom on the string. These string types are used on long laterals and can be less expensive to manufacture than monowall.

The coiled tubing string is stored on a reel and is usually mounted on a trailer for easy transportation. The reel is typically offset open spoke type with square and rectangular steel tubing, and has heavy duty roller bearings that are moved transversely by hydraulic cylinders to evenly spool the coil on the reel.

Most coiled tubing string assemblies also include a weight indicator and stripper / packer. The weight indicator measures the amount of load applied to the coil and then gives an indicating signal to the control cabin. Compression on the weight indicator due to increased tubing load or overpull from an injector will pressurize the fluid within the coil and give a positive deflection on the weight indicator while compression downhole from hole friction or obstruction will lighten the coil and give a negative deflection on the weight indicator.

Injector Head

Injector head assemblies are a vital piece of equipment for the coiled tubing drilling industry. They allow operators to drive and retrieve the coiled tubing within wells with pressure or to feed it into an out of well. In most applications, a downward thrust or upward pull on the coiled tubing reaching a maximum of 40,000 to 60,000 pounds (18,150 to 27,215 kg) is achieved with injector heads. Larger units are also available for use with coiled tubing of larger sizes.

Injector heads vary in design and construction from manufacturer to manufacturer. Most are comprised of a pair of Coil Pipe Assemblies opposed endless chain loops that carry a plurality of gripper blocks.

These gripper blocks are designed to grip the coiled tubing while being moved inside of a well. When a coiled tubing string is inserted between the opposing endless chain loops of an injector head, the gripper blocks grab the coiled tubing and hold it within the wellbore while moving the coiled tubing in the direction indicated by the double arrow 206 in FIG. 7.

The coiled tubing may vary in diameter from approximately 1/2” to 3”. Even larger sizes are anticipated to be used in the future, but the current majority of coiled tubing applications involve coiled tubing having a diameter less than 3”.

Typically, the two opposing endless chains loops 2 of an injector head have a fixed drive sprocket 4 at the top and a floating sprocket 6 at the bottom. These sprockets have provisions to move up or down in a slot 8 but are not able to move sideways, which helps prevent excessive wear on the chains 2.

Another aspect of this invention is a method of automatically adjusting the tension of a chain in an injector head used in coiled tubing systems. This method includes preventing the floating bottom sprocket from moving toward the first end of the chain loop using a mechanical stop; and automatically maintaining the chain loop at the desired chain tension by using a tension cylinder.

Injector head chains and skate bearings are subject to a lot of abuse during the course of a drilling project, and many failures occur due to improper chain tension. This is particularly true of those with a mechanical stop, which forces the sprocket down to prevent it from moving toward the first Coil Pipe Assemblies end of the loop. This creates a very high chain tension that can result in overheating and chain slippage, which leads to premature wear and damage to the skate bearings.

Bottom Hole Assembly

The bottom hole assembly is a set of components used on the drill string to provide force to break the rock, survive the harsh mechanical environment and allow the driller to control the direction of the well. It typically includes a drill bit, bit sub, a mud motor (in certain cases), stabilizers, drill collars, heavy-weight drillpipe, jarring devices (“jars”) and crossovers for various threadforms.

Assemblies of this type are primarily used on drilling rigs. They can be installed directly into the borehole or at a separate location within the well, which allows for easier access to the bottom hole.

In one particular form, a dual coil airbrake tubing assembly is constructed for connection within the airbrake system of a tractor/trailer rig or other like vehicle for supplying air pressure from a source thereof to an airbrake system of the vehicle. The tubing assembly comprises flexible, elongate first and second tubing members, 12a,12b, each having an outer surface and extending axially from a forward distal end to a rearward distal end. These tubing members are wound intermediate the forward and rearward distal ends of the tubing members radially about a generally cylindrical surface space to define a pair of expandable, self-retracting coil portions, 38a,38b.

Depending upon the number of turns or revolutions which are formed into the tubing members, each coil portion 38 may be of any length, but preferably extends coterminously along a central longitudinal axis, 36. A unitary sheathing member, 14 commonly surrounding the first and second tubing members and extending intermediate the forward and rearward distal ends, is provided to consolidate each successive pair, one of which is referenced at 58 for turns 39a,39b, of adjacent turns of the individual coil portions 38 as the coil portion 38 is extended and retracted by mutual, spring-like movement.

The sheathing member 14 may be fabricated from a thermoplastic material containing a core of extruded, heat-treated or vulcanized abrasion resistant material. Optionally, a polyester or other fiber reinforcement braided over the core may be incorporated into the sheathing. The sheathing may also be insulated for thermal protection.


Coil pipe assemblies are available in various forms and can be used for a variety of applications. The coil pipe itself may be welded or rolled and welded, depending on the application and requirements. Commonly used materials include low carbon steel, stainless, and ductile iron. Other materials such as AWWA piping, copper, and brass may also be used.

Coils are typically stored on reels that are driven by a hydraulic motor. The reels are designed to be able to coil the tubing under constant tension and uncoil it when required. The coiled tubing is then placed into the injector head to be lowered into the well.

In order to prevent the leakage of fluid from a coil tubing string when it is injected into a well bore, a method is provided for the use of a seal assembly for supplying a high-pressure fluid seal around the first and second coil tubing strings that are connected to a downhole tool, or that are inserted through the respective bores in the seal plate 22. The method of providing a high-pressure fluid seal around the coil tubing strings includes the steps of forming a packing chamber 34 on the periphery of the seal plate 22, and supplying lubricant through passages 36, 44 to the annular seals 36 and 44 to lubricate the seals while the first and second coil tubing strings are injected into and extracted from the well bore.

The lubrication is necessary because the frictional force of the tubing moving past the annular seals 36 and 44 produces heat that can damage the seals. The lubrication of the annular seals is particularly desirable because it allows for better sealing of the coil tubing strings, which will reduce the likelihood of fluid leakage during the injection and extraction processes.

In addition, the lubrication can help to avoid a situation where the coil tubing strings become stuck in the well bore. This can cause the well to fail and can be particularly hazardous when a blowout preventer is in place. The lubrication of the seals can also help to prevent the string from being pulled out of the well, which can cause a major accident.