What is Coiled Tubing?
Coiled Tubing is a long continuous steel pipe used to perform well completion, well intervention or workovers on a live well. During these processes, different types of fluids are pumped into the Coiled Tubing to operate and complete both onshore and offshore applications. Often Coiled Tubing has an outside diameter often ranging from ¾ – 5 ¼ inch and is typically wound on a large reel or installed on a Coiled Tubing unit reel.
History of Coiled Tubing?
Coiled Tubing was first developed during the Second World War for Operation PLUTO (Pipe-Line Underwater Transportation of Oil)
How is Coiled Tubing made?
Coiled Tubing strings are made from multiple flat cuts of hot rolled sheet steel, called master coils. These master coils are then placed into a mill that turns the flat sheet into a continuous rolled tube. From there, the rolled tube is formed into a long continuous steel pipe with lengths that can go for miles.
During the milling process, several tests are performed on the tubing. Eddy-current, laser micrometer (OD measurements) and UT (wall thickness) are data logged during milling. After the string is milled, it is rolled or installed onto a shipping spool. From here it goes through a series of mechanical and integrity tests including tensile testing, flattening testing, metallographic examination, and hydrostatic testing. Finally, the string is purged of fluids and inhibited for corrosion and installed onto a Coiled Tubing unit where it becomes operational ready.
Who makes Coiled Tubing?
There are only a few Coiled Tubing Manufactures in the United States, one of those being Global Tubing. Global Tubing’s manufacturing facility is located in Dayton, Texas. Global Tubing can produce outside diameter sizes that range from 0.750 inches (19.1 mm) to 5.000 inches (127 mm) with wall thicknesses from as small as .087 inches (2.00 mm) to as large as .337 in (8.6 mm). Global Tubing’s proprietary steel chemistry, experienced manufacturing and technical personnel, state-of-the-art mill technology and digital control systems deliver consistently higher quality products. Global Tubing also has several service center locations:
1. Dayton, Texas, USA (Manufacturing Facility and Service Center Headquarters)
2. Houston, Texas, USA (Forum Energy Technologies Office)
3. Midland, Texas, USA (Service Center)
4. Smock, PA, USA (Service Center)
5. Red Deer, AB, Canada (Service Center)
6. Grande Prairie, AB, Canada (Service Center)
Typical Coiled Tubing Equipment
Coiled Tubing Unit (CTU) – Equipment consisting of components which usually include a Control Cabin, Coiled Tubing reel, and Coiled Tubing, Injector Head, Goose-neck, Power Pack, and well control components.
Coiled Tubing Reel – Component of Coiled Tubing unit used to spool string. Includes level-wind guides tubing for efficient spooling; can be mounted on CTU or trailer. It can also be connected to fluid pumps and/or nitrogen pumps.
Power pack – System that provides power to the Injector, BOP’s, Reel, and Control Cabin. Also provides back-tension during operations. Systems are available in either hydraulic or electric-over-hydraulic.
Control Cabin – located behind a Coiled Tubing reel on a CTU, or as a separate unit in offshore operations, a control cabin houses all the controls necessary to operate a Coiled Tubing unit
Injector Head – Facilitates the entry of a Coiled Tubing string into the wellhead stack, regulates direction (run in hole or pull out of hole), and speed of the string. It is controlled by the operator in the control cabin with the use of a closed loop hydraulic system.
B.O.P.’s (Blowout Preventer) – Used in case of emergency to maintain well control.
1. Main BOP – Consists of: Slips, Pipe, Shear, and Blind
2. Combo B.O.P. – Used in addition to a regular B.O.P., combines Shear & Blind and Pipe & Slips
Fluid Pumps – Pressurize fluid that is pumped down Coiled Tubing string, usually in a tandem configuration.
Nitrogen Pumps – supply Nitrogen gas to Coiled Tubing inlet, either to pump pure nitrogen for lifting operations, or nitrified fluid in commingled operations. Can efficiently purge Coiled Tubing dry.
Crane – Holds up injector and riser assembly. Commonly contracted to a 3rd party company. Cranes may not be required for some specialized Coiled Tubing rig-ups, such as automatic mast Coiled Tubing units or Tower set-ups.
Flowback Equipment – connected to the Christmas tree as an outlet for produced fluids during operation. Used to control the backpressure / effective wellhead pressure for specific Coiled Tubing operations.
Advantages of Coiled Tubing?
1. Able to perform operations without killing the well. In a conventional workover operation, the well needs to be killed before the Coiled Tubing operation can be safely performed. Coiled tubing jobs can be performed with the live well in a balanced (barrel-in-barrel-out) operation.
2. Formation Damage is minimized
3. Mobility – Coiled Tubing rig up and rig down can be performed in a day whereas, workover rigs can take up to a week to rig up and down
4. Time – service time is reduced significantly compared to joint tubing since Coiled Tubing is continuous and has no connections to make or break
5. Safety – with reduced manual pipe handling, safety is improved for crews and personnel.
6. Overall cost – Coiled Tubing is more cost-efficient per hour because of the increase in efficiency, and workover duration is drastically reduced
Coiled Tubing Application
Millout / Drillout
Zonal Isolation / Sand Control
Tubing Conveyed Perforation
Future of Coiled Tubing / Technology / Technical Advancements
SMARTaper – Global Tubing’s patented Coiled Tubing technology which eliminates bias-weld fatigue spikes for longer running lengths. SMARTaper increases horizontal reach and adds strength in high-fatigue zones while managing the overall weight of the Coiled Tubing strings.
DURACOIL – technically advanced, cost-efficient Coiled Tubing for service in challenging downhole environments. DURACOIL has been tested to improve tubing fatigue life, predictability and resistance to abrasion, , and able to perform exceptional in high-pressure environments
Trends – as well depth begins to increase, so does the complexity of the Coiled Tubing string design. Advancements in bottomhole assemblies / tools, chemical additives and friction reducers that reduce helical buckling