Casing Leak: Basics

Casing leaks are not uncommon in oil and gas wells. These leaks are often noticed during the well construction phase or during workover of older wells.

It is normal practice to pressure test the casing string to verify that well integrity is intact before continuing further operations on the well. This is standard procedure for both new wells and older wells during workover.

Casing leaks are often a result of leaking casing threads, burst casing from pressure, corrosion or from casing wear due to extended periods of drilling operations.

Wells that are specifically prone to casing wear during drilling is extended reach wells and multi-lateral wells, due to the multiple drilling trips and long periods of drilling operations taking place through the same casing. The wear from the drill string rotation can in these cases wear a hole in the casing.

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Casing Leak
 
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The challenge in a nutshell

A casing leak is a failed barrier. Consequently, a casing leak can lead to sustained casing pressure, leaks into a formation that should be isolated, or in some cases even loss of circulation if the leak is big enough and the formation cannot hold the hydrostatic pressure.

In the case of fluid losses, a casing leak can escalate become a serius well control problem.

Maintaining proper barriers and casing integrity is even more critical if the well is going to be fractured with high pressure. There is a chance the treatment pressure can hit the wellhead or one of the annuli with lower burst rating than the planned frac treatment pressure.

What options are at hand to remedy casing leak?

If there is a casing leak, how can you save the well? Once it is evident from pressure testing or through fluid losses that a casing leak exist, locating the leak interval in the casing must be done.

Depending on the leak, this can be done with logging tools, but the most common method is to use a multi-set, retrievable packer on a workstring to do multiple pressure tests of sections of the casing to locate the leaking casing interval. When the leak area has been located, there are multiple cures that can be applied.

Straddle packer or Casing patch

A mechanical method of placing a straddle packer or a casing patch over the leak interval is a well proven method in the industry and works well.

This does however reduce the ID of the casing section where these tools have been placed. It can be costly if the leak section is long and finding a good spot for the sealing elements can be hard if the casing is suffering from heavy corrosion or groves have been created in the casing ID by drillstring wear.    

Cement

Cement is the most common cure for casing leaks, it is usually the first remedy to be tried. Cement is normally a low cost material to pump and can be used to seal longer sections of leaking casing. The typical method is placing a balanced cement plug across the leaking interval on top of a retrievable bridge plug, cement support tool (CST) or other remedies set just below the leak interval - and then squeeze cement into the leak path.

Despite that cement is a low cost material to pump, it can become expensive to use due to rig cost. It is not uncommon that multiple cement plugs must be pumped before a seal has been created, this could take several days. The cement has particles that bridges off in small cracks and pores, that can make it hard to squeeze off and seal the smallest leak paths. If a seal has successfully been created and been verified by a positive pressure test, after the cement inside the casing has been drilled out, getting a successful negative pressure test is even harder.

Resins

Wellcem have proven multiple times that ThermaSet resin technology is far more successful in sealing casing leaks than for example by using cement. This is why the Wellcem solution is gaining popularity as another remedy for casing leaks.

Using resins to seal leaks in the casing leak intervals

The ThermaSet sealing system is a very low viscosity, particle free resin based system that is not miscible with water. It can handle large amounts of hydrocarbon contamination and still cure into a strong material.

This means it will work well in formations that are both water or oil wet, it will penetrate the smallest leak paths and tight formations and form a sealing material with up to 10 times the compressive strength of cement and with a flexibility that can handle casing ballooning and casing movement without breaking.

These material properties is the reason that casing leaks can be repaired with a very high degree of success using common cement placement methods. Both positive pressure tests and negative pressure tests after treatment will in most cases be successful.

The placement methods are most often the same as for cement as described above. For ThermaSet, the efficiency in sealing and creating the permanent seal with just one treatment is very common. Doing treatments in two steps is only needed for very complex cases.

ThermaSet can be pumped into the annulus, tubing or casing interval that needs to be treated and gravity does the rest. As ThermaSet is not miscible with water, it will drop through water-based fluids and reach the treatment area intact and undiluted. ThermaSet resin can be tailored to each application and the density can be tailored from 0.7 to 2.5 SG. For very small leaks even wireline conveyed dump bailers or other small volume tool methods can be used to place the treatment where it is needed.

If you want to get more insight to resin-based solutions like ThermaSet for Casing Leak, click here:

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You may also want to learn more about other areas of application like Lost Circulation and more, just scroll down ->

The most common causes for leaks in oil wells_TOFU

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Applications for the Wellcem solution

Application

Plug & Abandonment

The primary objective is to ensure that no leaks to surface exist and that no formation fluid migration occurs even many years after the well has been abandoned.

Application

Zonal Isolation

Most oil and gas wells have different zones. Zonal isolation seeks to segregate undesirable intervals from production.

Application

Sustained Casing Pressure

Regardless of definition, either SCP, SAP or CCA, it is a well integrity issue with a failed barrier. It requires management or workover.

Application

Casing Leak

Casing leaks are often a result of leaking casing threads, burst casing from pressure, corrosion or from casing wear due to extended periods of drilling operations.

Application

Lost Circulation

Lost Circulation means you are losing your circulation of fluids off to a low-pressure and permeable formation somewhere in the well.

Application

Control Line

Many wells have a hydraulic control line running down along the casing or tubing. Control lines can develop an undesired leak.