Fall 2008
Considerations for Fracturing
with Resin Coated Proppants

After a hydraulic stimulation treatment is complete and all the equipment is rigged down and taken off location, the only thing left to maintain communication to the reservoir is the proppant. There are many different types of proppants, ranging from walnut hulls to man-made high strength ceramics. Each of these options has applications where they will provide efficient flow capacity to produce the given formation. The latest technological advances in resin coated proppants can greatly improve and strengthen the base proppant to improve the fracture treatment results.

Types of Resin Coatings
There are three types of resin coatings: precured, partially cured, and curable. Each is designed to improve the strength and technology of the base proppant to meet long-term production goals. However, there are differences between them that can have a major impact on the expected results.

Precured Resin Coatings
A precured resin coating is designed to increase the strength of the individual proppant grains. It does this by putting a thin deformable coating on an otherwise rigid surface. This deformable coat allows for an increased area of grain-to-grain contact to more evenly distribute the point stresses.

With the increased surface area of grain-to-grain contact, less grain failure occurs, leading to reduced fines generation over uncoated proppant. Resin coated proppants also have the ability to encapsulate any fines that are generated due to grain failure. Fines that are not encapsulated are likely to migrate through the proppant pack and reduce fracture flow capacity.

Although a precured resin coated proppant has the ability to reduce fines and strengthen an uncoated proppant, it does not have the ability to prevent proppant flowback. Proppant flowback damages surface equipment and reduces the communication between the fracture and the wellbore. To prevent flowback, a partially cured or curable resin coating is required.

Partially Cured or Curable Resin Coating
Partially cured and curable resin coatings are different, but exhibit all of the same properties except one. This type of resin coated proppant has added benefits over a precured resin coating. Due to its ability to bond, there is a greater reduction in fines generation since the surface area of grain-to-grain contact is larger. Instead of just a single grain making contact with another grain, there are multiple grains bonded together in a network of deformable surfaces. This unified proppant pack increases the distribution of stress on the proppants within the fracture, decreasing the stress on each individual grain.

The ability to bond not only reduces the amount of fines generated, it also reduces the amount of loose fines that are able migrate through the proppant pack. When grain failure occurs with a precured RCP and the resin fails, loose fines are generated. These fines are then mobile and can plug the pore spaces of the proppant pack. With a resin coating that has the ability to bond, even if the proppant breaks, the network of grain-to-grain bonds prevents the fines from migrating through the pack and reducing flow capacity.

This type of resin coated proppant also reduces the effects of embedment into the formation which is very critical for waterfracs in shale formations where narrow frac width is desired. The ability to bond provides a larger surface area for the formation stresses to act upon. The consolidated pack prevents embedment over time and allows for a wider frac to be maintained throughout the life of the well.

The improvements seen with this type of resin coating over a precured resin coating are all related to its ability to bond and create a consolidated proppant pack. A consolidated pack also prevents the proppant from flowing back out of the fracture. Flowback can reduce near wellbore fracture width to the point where communication between the fractures and the wellbore is lost.

Even though there are many benefits achieved through bonding, it can be detrimental if the bonding occurs at the wrong time and in the wrong location. A major benefit of partially cured, “stress-to-bond” proppants is that they require the correct amount of temperature and closure stress to create a bond. This occurs under the conditions in the fracture – not in storage or in the wellbore. Curable proppants only require temperature to start the bonding process. Bonding that occurs in the wellbore can cause costly cleanouts that require drilling or acid treatments to remove the proppant from the wellbore. “Stress-to-bond” proppants left in the wellbore can normally be flowed out or washed out with coil-tubing.

Resin coated proppants are available on many different substrates of varying size and strength to fit a variety of downhole conditions. When deciding on a proppant, it is important to consider fines migration and proppant flowback instead of basing the decision solely on baseline conductivity data. Keeping all these factors in mind will allow you to choose the correct proppant for the specific conditions of the well. This will lead to increased production and ROI while eliminating the costs associated with the problems that can occur. From shallow slickwater fracs to the most extreme conditions in HPHT wells, there are resin coated proppants designed specifically for all your completion needs.


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