Casing Leak

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.

From the Well Integrity Blog: This is how we dealt with a leaking liner lap

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.    

From the Well Integrity Blog: 6 ways to prevent well integrity problems

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.

Download Free Ebook: Guidelines for setting Cement Plugs

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.

From the Well Integrity Blog: The resin curing process