Endeavor Management’s Keith Caulfield and Mike Cowan examine the results of a recent JIP that showed resin may be a potential alternative to cement in P&A operations.
Endeavor Management recently completed a joint industry project (JIP) covering covering several subjects related to the decommissioning industry. One that was of intense interest to JIP member companies was the use of resins for well plugging and abandonment (P&A).
Endeavor Management has researched the potential for resin as an alternative to cement. We set out some of the conclusions here.
For years, resins have been viewed as a dramatic upgrade to cements for many uses in well construction, remediation, and P&A. However, three factors have contributed to keep resins from being more widely used: the “durability gap,” dealing with uncertainty of the long-term durability of resins, the “knowledge gap,” created by the lack of resin-trained industry personnel, and the perception that resins are much more expensive than cement.
Any P&A barrier must create a “sealing boundary” between the different regions of a well:
- Sealant/outer casing surface
- Sealant/inner casing surface
Cements are placed as a liquid full of solids-in-suspension. As cements hydrate, they cure into a rock-like solid. Any seal created is predominantly mechanical.
At the interface between cement and formation, the solids-laden cement does not penetrate very far into the pores, leaving a seal that exists virtually at the formation wall. This interface can follow variations in the mating surface. There can be a chemical bond component to formation and casing, but the overall sealing bond is mainly a mechanical bond defined by friction and a solid-to-solid interface.
A broad analogy describing the way cements seal is “the clamp.” A clamp applies mechanical load (compression) to the items being secured. Mechanical seals in a clamped joint need the force provided by the clamp to create the seal. As long as the clamp remains, the system is stable. Move, jiggle, or relax the clamp and the properties of the entire system are changed for the worse.
For resins, the sealing mechanism is completely different. At the formation interface, resins – being liquid during placement – penetrate far deeper into the formation than cements. With resins, the sealing interface is actually out in the formation instead of being at the interface. At the interface between well and formation, resins seal by spanning this interface, rather than sealing at the interface.
There is a chemical bond between resins and the casing. A well-formulated resin can achieve characteristics similar to a heavy-duty radial tire, with no matrix permeability and good adhesion to the various well surfaces. Cements cannot do this.
Simply put, resins have material properties more tolerant of the differential stresses that can cause barrier failure.
An analogy that best describes the way resins seal is “the glue.” A glued joint, especially with glue forgiving of relative movement, only needs clamping action (external force) until the glue cures. After that, the clamp can be moved, jiggled, or relaxed at will; the glued joint will remain intact. After curing, the glue seals by chemical bond.
With the right type of glue, a glued joint will last far longer than a clamped joint. In similar fashion, a well-chosen and well-placed resin barrier can last far longer than a cement version. So, if you move, jiggle, or relax the clamp on a glued joint, the ‘glue’ (resin) will still seal while a clamp-dependent mechanical seal (cement) will not.
While the “clamp” (structure) of any oil well is typically very robust, what might happen to these “clamps” over geologic time frames? When you replace the cements with correctly-engineered resins, the barriers no longer remain dependent on the “clamp” for effectiveness; they can seal even if things happen to the formation interface.
As shown above, there are many ways that resins can effect a “step change” improvement in reliable well barriers. There is general agreement among cementing experts that resins will seal problematic well interfaces differently and more effectively – If these better seals can be trusted for the time frames necessary in permanent well P&A.
There is no better time to move forward and remove that big “IF” from this situation. It becomes obvious that a subject ripe for industry collaboration is to determine the “price tag” for a thorough study of the long-term durability of resins as effective sealing barriers in oil well utilization.
Knowledge and cost gaps
Factors that have combined to keep resins from being more widely used include:
- Cements are far more established in the industry, having been used since its beginnings.
- Knowledge of where and how to use cements is very common.
- Resins have varied formulations that can be custom-fitted to nearly any well situation. However, practical knowledge is limited to few people or organizations.
The use of cements as a major component of well construction has generally been successful, when viewed from a historical perspective. Stated perhaps too simply, these demands have been to get the resources out of the ground economically and without hurting anybody. In the last 50 years, they were augmented to include “and do no immediate harm to the environment.”
The decommissioning industry must consider time frames far beyond the scope of any past oilfield activity: the demands of geologic time, taking into account not only the present, but extending thousands of years forward. This new perspective forces us to look for a better sealing material.
Small numbers of people know enough about resins to enable change to occur across the breadth of the industry. If resins are to improve the quality of well P&A sealing, then much effort needs to be put into wider education around how to best use them.
The industry could collaboratively help establish an educational program that will spread the specialized knowledge of resins to benefit the industry. A field guide for resins will be needed for the future, just as cementing guides exist today.
The cost per unit of resins can be 25-40 times the cost of cement. However, resins’ high material costs can be overcome with field operations that fully exploit their technical advantages.
There are three gaps that must be bridged for the use of resins to become common, even though they provide an improved sealing mechanism quite different than cements. If two of these gaps – industry knowledge and proof of their durability – are closed, the third – resins’ higher material costs – can be demonstrated to be less that cement on an installed basis using field techniques that offset these costs and enable a true step-change improvement in well sealing.