Plug and Abandonment (P&A) of a well involves plugging back a wellbore and temporarily securing it for a few months to years or permanently with an eternal perspective in mind.
In most areas, the retirement of assets is outlined by the national regulatory agency. 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.
In places where no national regulations exist, oil companies typically implement their own standard procedures for how to safely plug back a well.
Plugging back a well is a standard operation in the life cycle of a well that all oil companies address when the well is no longer useful or becomes unprofitable. This is not an operation that generates revenue and is purely an added expense that must be completed as quickly and cheaply as possible while adhering to regulatory guidelines.
Older wells often suffer from annular leaks or a loss of casing integrity that can further complicate the P&A operation. These cases often require the operator to cut and pull tubulars or section mill casing in order to gain access to the leaking interval and seal it off.
The majority of standard P&A operations require a rig that immediately introduce increased costs to the operator. Typically plugging back of wells utilize cement or a combination of mechanical plugs and cement.
Mechanical sealing methods of placing a plug in a cased part of the well is a proven concept across the industry. Quite often casing integrity is compromised due to the age of these assets and can be unreliable as a result of corrosion or tubular erosion. Identifying an intact setting depth for sealing elements can prove difficult and ultimately result in failed pressure tests.
Cement is the most common material used for P&A. Placing several cement plugs on top of mechanical plugs set at various depths in the well is a common abandonment technique. If the well is intact with no difficult leaks detected outside the inner casing strings and the completion can be pulled without any issues, the placement of mechanical and cementitious plugs is a straightforward and reliable method for P&A.
Complications with well abandonment arise when annular integrity is compromised. In order to gain access to the compromised annulus the casing must be cut and pulled, section milled, or perforated. The annulus is then typically sealed through conventional means by placing a cement plug across the target interval and squeezing cement into the leaking annulus. This can become difficult due to the inherent limitations of cement. A cement slurry is comprised of particles that can bridge off in small cracks and pores and make it difficult to squeeze off and seal small leak paths.
Other wells can have various problems with the completion, it could be leaking, broken, split, collapsed. Casing could also be collapsed. All these issues could make it hard to do a conventional P&A because you may not get to the area you want to treat with a work string.
When the well provides extra challenges, Wellcem’s resin technology and solutions can be a good alternative. Wellcem has proven multiple times that ThermaSet® resin technology is far more successful in sealing an annulus than for example by using cement.
The resin can also be made light or heavy and because it is immiscible with water, it can reach places cement cannot because cement will be diluted on the way. Therefore, the Wellcem solution is gaining popularity in P&A operations.
Wellcem’s ThermaSet permanently seal leaks in oil and gas wells. The placement methods are most often the same as for cement, but in some cases where access is difficult and we have mostly water or water-based fluid in the well, ThermaSet can be gravity fed to the place it is needed.
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 adjusted from 0.7 to 2.5 SG.
Recommended reading: Resin curing process
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 areas that are both water or oil wet, it will penetrate the smallest leak paths and tight formations and form a permanent and lasting seal with a flexibility that makes it a much more robust seal that for example cement. ThermaSet® has also been proven to last for a very long time (thousands of years) in most normal downhole conditions.
If you want to get more insight to resin-based solutions like ThermaSet for P&A, click here:
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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.