Zonal Isolation

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.

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?