Coiled tubing is used for a variety of different completion, drilling, and intervention operations.
Today we will take a look at the 18 most common coiled tubing operations.
18 Most Common Coiled Tubing Operations
1. Coiled Tubing Milling
Coiled tubing milling is the most common coiled tubing operation.
Bridge Plugs Milling
In most cases, coiled tubing is used to millout bridge plugs after the well is fractured.
Most plugs are designed to be easily milled out to decrease the time required for the milling operation so that the wells can be put on production as soon as possible.
A few plug manufacturing companies even provide dissolvable plugs that dissolve with time and in theory, don’t require milling.
However many oil companies still use coiled tubing with a milling BHA to run in a well and confirm that all the plugs have dissolved before putting the well on production.
Related: What Are Bridge Plugs In Oil And Gas?
Frac Ports Milling
Some operators also use coiled tubing to millout frac ports.
Removing frac ports can increase production and helps to avoid possible issues down the road.
In theory, frac ports can act as settling spots for sand and wax.
Casing Deformation Milling
Milling is sometimes also used to remove the casing deformation often caused by issues encountered while fracturing the well.
A special milling bit is used to dress the casing and the deformation.
Cement Milling
When an improper cement job is done, sometimes cement can get into the casing and you might end up with a few hundred meters of cement at the toe which needs to be milled out.
In more severe cases it can be up to 1000 m of cement.
Cement milling is a pretty slow operation that requires proper pH control but in most cases, it is cheaper than drilling another well or abandoning a portion of the well.
Related: What is Cementing in Oil and Gas?
2. Clean Outs
Cleanout is a very common coiled tubing operation as well and is often used to clean the wellbore on older wells where production dropped off because of sand or wax buildup in the well.
It can also be used to remove sand during the screen out while fracturing.
Because cleanouts are often performed on older well with lower bottom hole pressure, nitrogen is frequently used to keep the returns.
Related: How Coiled Tubing Wellbore Cleanout Operations Are Performed?
3. Confirmation Runs
Confirmation runs are often performed before the frac to ensure that the wellbore is clean and to remove any cement at the toe.
Cement at the toe can prevent the toe port from opening.
4. Logging
Coiled tubing is often used for cement bond logging (CBL) to check the cement integrity between the casing and the formation.
There is also a trend in the industry towards injecting fiber line into the coiled tubing string and using it for logging operations to find out which zones are producing.
5. Camera Runs
Similar to logging, the camera can be run on a coiled tubing string to get a better understanding of downhole conditions.
The camera usually has a built-in battery and memory.
The battery life will limit how long the camera can be in the well.
Another option is to run a camera on e-coil which is basically coiled tubing with an electrical cable inside.
6. Frac Through Coil (FTC)
Fracturing treatment is pumped through the coiled tubing.
Usually, 2 7/8” coiled tubing is used to allow required rates to be pumped.
7. Annular Frac
In the case of annular frac, the treatment is pumped down the casing/coiled tubing annulus.
Annular fracturing is common with completion systems that have shifting sleeves that can be opened and closed.
One example is the NCS multistage system.
Related: What is Hydraulic Fracturing?
8. Tubing Conveyed Perforation (TCP)
Sometimes coiled tubing is used to run TCP guns to create perforations in the casing before the well can be fractured.
Often wireline is used to run TCP guns but in some cases where the toe port can’t be opened coil is used instead.
9. Abrasive Jetting
Similar to TCP abrasive jetting can be performed with coiled tubing to create perforations in the casing before frac.
Abrasive jetting is usually used to create additional perforations on older wells during the re-fracturing operations or to add additional zones when shifting sleeves malfunction.
Related: What is Perforating?
10. Acid Stimulation (Acidizing)
Acid can be pumped down the coiled tubing to stimulate the formation.
This is common in carbonate formations.
11. Fishing
Coiled tubing can be used to retrieve various tools left downhole.
This can be anything from TCP guns to any other pieces of downhole tools.
Using proper fishing tools can significantly decrease the amount of time required to retrieve the fish.
Improper tools, job design, or challenging well conditions can result in weeks of fishing.
Sometimes a camera is used to analyze the fish before running with fishing tools.
Related: What Is Fishing In Oil And Gas?
12. Opening and Closing Sleeves
Coiled tubing can be used to close and open sleeves if a sleeve system is used.
This is usually done after fracturing operations.
13. Velocity String
Coiled tubing can be used as a production string for some wells.
This is usually accomplished by running coiled tubing to a certain depth and then cutting it at the surface and leaving it downhole.
14. Well Nitrogen Kickoff
If the well is not producing because of low bottom hole pressure (BHP) sometimes coiled tubing can be used to pump nitrogen down the well to decrease the hydrostatic pressure of the fluid column and bring the well back online.
Related: How is Nitrogen Used in the Oil and Gas Industry?
15. Setting and Retrieving Bridge Plugs
If a specific part of the well needs to be isolated, either a temporary or permanent bridge plug can be used for that.
Coiled tubing is often used to set or remove the plug.
16. Hydrate Removal
Hydrate removal is similar to cleanouts but instead of regular fluid, hot water or methanol are used to remove the hydrate that might be blocking the production.
Special attention has to be paid when designing a hydrate removal job because there is a potential for pressure buildup under the hydrate.
17. Casing Patches
Sometimes hydraulic fracturing operations can cause damage to the casing.
This often happens in the heel section of the well which prevents the operator from continuing the fracturing operation.
One way to fix this damaged casing is to apply specially designed patch that covers the damaged section of the casing.
Coiled tubing is often used to run a casing patch in the well because it allows a high degree of accuracy when placing the patch as well as provides an option to set a specific amount of weight on the patch to secure it.
18. Coiled Tubing Drilling
Coiled tubing is sometimes used to drill shallow wells or for re-entry drilling.
One limitation of coiled tubing is that the pipe cannot be rotated as well as the amount of force that can be transferred to the bit decreases significantly with the depth.
This makes it challenging to use coiled tubing for drilling deeper wells.
Read next: Coiled Tubing Bottom Hole Assembly (BHA) Components