Coiled tubing is a specialized type of flexible piping often used in the oil and gas industries. These tubes usually come in diameters from 1″ to 3 ¼” and are used primarily for well interventions and production in depleted gas wells. It’s viewed by some as an alternative to wireline or joint tubing rigs for completing the same general operations, but industry insiders know that using coiled tubing in well interventions is much more effective.
Advantages of Coiled Tubing for Well Interventions
Those interested in coiled tubing but used to implementing other, less efficient, and more dangerous, solutions may need a little incentive to make the switch. Thankfully, there are plenty of coiled tubing advantages that should change their minds about whether it’s worth changing to a different process.
Coiled tubing can be deployed and retrieved without disrupting the circulation of fluids, and it can be placed into operation while surface pressure is present, which means well operators don’t need to kill the well. It also takes longer to service a well with coiled tubing than wireline or joint tubing because there are no connections to form or break. The tubing can be coiled onto giant spools to be retrieved intact.
Well operations that use coiled tubing can usually maintain a smaller staff because of the piping material’s compact and highly mobile nature. The personnel responsible for operating the well will also be subjected to fewer safety risks since coiled tubing has minimal pipe handling needs. To make matters even better, coiled tubing is less likely to damage the well itself when used appropriately, and it can be retrieved and reused once the job is done.
Common Applications for Coiled Tubing in Well Operations
Maintaining and operating gas and oil wells is tough work. The experts tasked with ensuring that these operations go smoothly deserve to have access to the best technology for the job. Investing in coiled tubing will allow gas and oil companies a chance to help workers while simultaneously improving their bottom lines. The tubing can be used for the following applications:
Sand and Solids Removal
Cleaning sand and solids out of wellbores requires operators to pump fluid into the well, introduce the solids into the wash, and carry them up to the surface, where they can be captured using surface return tanks. The fluids can then be recirculated to the wellbore to optimize cleanout processes. Coiled tubing offers an effective and efficient way to transport sand and solids out of the wellbore and recirculate the wash water back in. It’s a perfect delivery method for both incompressible and compressible cleanout fluids.
Circulation and Deliquification
Hydrostatic heads can kill wells by inhibiting the flow of formation fluids as a result of their weight. Deliquification and circulation are safe and effective options for circulating the fluid out. The operators simply need to run coiled tubing to the bottom of the well and pump in nitrogen gas to force the kill fluid out.
Traditional methods for dispersing fluids to specific locations in the well to cement perforations or perform chemical washes are not very efficient. Operators have to pump the cement from the surface, allowing it to flow through the entire system and potentially damage essential components like downhole safety valves. Coiled tubing offers a much safer solution. Coiled tubing umbilical technology allows operators to deploy complex pumps that eliminate the number of units required and reduce the risk of damage to the well.
Coiled tubing can also be used as a production string, specifically in shallow gas wells. Its narrow internal diameter creates a higher velocity than conventional tubing or casings, which makes it easier to lift liquids to the surface that might otherwise accumulate in the wellbore. Operators can run coiled tubing inside both traditional tubing and casings. They can also use coiled tubing umbilicals to convey hydraulic and electric submersible pumps or jet pumps for service applications or deliquification.
Logging and Perforations
Logging is traditionally performed with a wireline. However, coiled tubing is better for the job since it is rigid and can be pushed in from the surface. The effective use of wireline depends on the tool string’s weight to be lowered into wells, and gravity alone is often insufficient for wireline logging in horizontal or highly deviated wells. That’s not a problem with coiled tubing. As a result, it’s often used to complete logging and perforating tasks following chemical washes.
Some oil and gas companies are now using coiled tubing to assist in drilling operations instead of conventional pipes. The advantage of taking this approach is that while drill pipe must be assembled joint-by-joint as it is deployed, coiled tubing can simply be run in. It can also be retrieved more easily.
When coiled tubing is used for drilling, operators deploy it via a stripper to create a hydraulic seal. The application of the hydraulic seal surrounding the coil allows operators to drill underbalanced and improves control capabilities.
Coiled tubing drills utilize different technology, including bottom hole assemblies and mud motors, allowing operators to effectively steer the drill bit to better control the well’s trajectory. While coiled tubing drilling remains less popular than the use of conventional drill pipes today because it requires investing in new technologies, it’s becoming more common as more companies make the switch.
In low-rate gas wells, coiled tubing can be used as vent strings or completion tubing. Operators can follow the same guidelines established for jointed tubing. As long as the coiled tubing is designed to handle the tension, burst, and collapse stresses that can occur during well operation, it will offer an easy to deploy alternative. Just keep in mind that it will be subjected to plastic deformation, which can cause accumulated fatigue damage. Coiled tubing may need to be replaced more frequently than jointed tubing.
The Bottom Line
Coiled tubing is a versatile material. It can be used in a wide variety of well interventions and operations. As the gas and oil industry’s interest in coiled tubing continues to rise, companies can expect even more innovations and new equipment designs.