Zonal Isolation - the basics

Most oil and gas wells have different zones that are exposed during drilling and completion.

If the well is a producer, it will normally have a gas or oil zone that the hydrocarbons are produced from. It is very common to have permeable formations with a desired hydrocarbon combined with other fluids sorted by density, with gas on the top, then oil and water/brine at the bottom.

Zonal isolation seeks to segregate undesirable intervals from production. This is accomplished during the well construction phase when casings and liners are cemented in place.

During the completion phase, zonal isolation can be achieved mechanically (e.g. packers) or through alternative methods.

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Zonal Isolation
 
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Why is this a challenge?

In many wells, producing the oil is the most desirable option. It is the most valuable fluid and the easiest to control/process. The problem is that both water and particularly gas flow much easier than oil and can dominate the production flow.

An ideal completion will ensure that only the desirable fluid is produced. This can be complicated to get correct as a well changes characteristic over the time it is in production in ways that are not always easy to predict.

  • Too much water is expensive to process and dispose of and can render the well uneconomical
  • Gas can be flared off; however this is becoming more and more uncommon in many areas due to environmental restrictions. It can become quite costly to treat, separate, store, and transport the gas, so minimizing its production is very often desirable

Zonal Isolation: What are your options?

If the completion assembly enables isolating a zone by closing a production sleeve, it can be very easy to seal off that zone. If it does not, zonal isolation becomes more complicated and some form of well intervention is then required.

Plug or Packer

In some cases, zonal isolation can be achieved with a mechanical plug or packer, or a packer assembly such as a straddle. In older wells this is complicated by worn and corroded sections of casing making it difficult to achieve a competent seal. Compromised tubulars can also prevent the conveyance of a suitable mechanical seal down to the relevant depth. To overcome some of these challenges coiled tubing can be used to accurately target an area for isolation by pumping a chemical treatment or cement.

Cement

Cement is the most common sealing material used and it is usually the first remedy employed due to its popularity, availability, and economical attractiveness. Despite the reduced cost of cement, operations can quickly become expensive if it fails to provide a seal. It is not uncommon to deploy multiple cement plugs over the course of several days prior to successfully establishing a seal., These attempts can also potentially damage the well in other areas. Cement is made up of particles that can bridge off in small cracks and pores, making it difficult to squeeze off and seal small leak paths. Additional challenges introduced by the use of cement involve slurry contamination. A cement slurry is heavy and will dilute significantly when exposed to water. Cementitious particles will settle and alter the design density of the slurry thereby compromising the system. Further contamination can occur if the cement slurry is exposed to hydrocarbons that can ultimately inhibit hydration.

Resins

ThermaSet® resin technology is able to overcome many of the challenges affiliated with these conventional solutions and has resulted in a high success rate for attaining zonal isolation. This success coupled with the streamlined proficiency of ThermaSet® is why the Wellcem solution is gaining popularity as a more robust sealing material for zonal isolation.

Additional reading from The Well Integrity Blog: Zonal isolation - What are effective alternatives to Cement?

ThermaSet may come to rescue for Zonal Isolation

Wellcem’s ThermaSet® permanently seal zones in a well to provide isolation. Placement adheres to the conventional methods described above; however, the efficiency of ThermaSet® lies in its ability to create a permanent seal with just one treatment.

As ThermaSet® is immiscible with water, it is resistant to contamination by aqueous based fluids. This property facilitates the spotting of a competent pill across the treatment area. ThermaSet® resin can be tailored to each application and the density can be adjusted from 0.7 to 2.5 SG to maximize placement efficiency. For very small leaks wireline conveyed dump bailers can be used to place the treatment where it is needed.

ThermaSet® is a very low viscosity, particle free, resin-based system that is immiscible with water. It can overcome large amounts of hydrocarbon contamination and still cure into a strong material, making it ideal for formations that are either water or oil wet.

ThermaSet® has the ability to penetrate extremely small leak paths and tight formations to form a permanent and long-lasting seal. The set product is flexible and can endure movement and changes caused by fluctuations in both pressure and temperature without failing.

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

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

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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.