January 13, 2017

Optimize Your Completion by Reducing Proppant Embedment

Well Challenges

Choosing the right proppant for the right application, instead of using the same proppant in every hydraulic fracturing application, can reduce cost per BOE. In a clay-rich, soft formation, for example, proppant choice is vital to reduce embedment.

What is embedment?
When completing a well in a clay-rich formation, such as the Niobrara in northeastern Colorado and adjacent parts of Wyoming, Nebraska, and Kansas, proppant can press into or embed into the formation and weaken stimulation effectiveness. Rather than increasing near-wellbore propped conductivity for greater hydrocarbon production, embedment reduces fracture width 10% to 60% (Core Lab 2015) and decreases production.

Causes of embedment
A clay formation, such as the Niobrara, has a low Young’s modulus (YM), also known as the elasticity modulus. This formation type is considerably different from a well-consolidated sandstone that has a high Young’s modulus. A low YM, one cause of embedment, can be degraded further by frac fluid and friction reducer; increasing reservoir pressure and temperature intensify this effect. Embedment can worsen as the formation softens and swells.

The wrong proppant, such as frac sand and ceramic, is the other cause of embedment in this low YM dynamic. Because frac sand and ceramic cannot form a consolidated proppant pack, these materials cannot decrease single-point loading or the force that causes a proppant grain to embed into the formation. The first 10% of embedment volume can reduce fracture conductivity between 45% to 80% (Zhang, Ouyang, Hill, and Zhu 2014).

Conditions of closure stress

How to reduce embedment
Curable resin-coated proppant with field-proven unconfined compressive strength (UCS) or bond strength is the best choice in soft formations to reduce embedment. Curable resin-coated proppant bonds and sets into a pack of solidified proppant grains, as opposed to loose frac sand or ceramic grains, with an overall greater surface area that redistributes and lowers single-point loading to maintain fracture width.

Conclusion
Formation characteristics are an important consideration when designing a completion. A clay-rich, soft formation is predisposed to embedment because of a low Young’s modulus that is degraded further by frac fluid and friction reducer. The second cause of embedment is the wrong proppant, such as frac sand and ceramic. Curable resin-coated proppant, which sets into a durable proppant pack, optimizes your completion by reducing embedment.

References
Core Lab. Advanced Rock Properties. corelab.com/ps/hydraulic-fracture-design.

Zhang, J., Ouyang, L., Hill, A.D., Zhu, D., 2014. Experimental and Numerical Studies of Reduced Fracture Conductivity due to Proppant Embedment in Shale Reservoirs. Presented at the SPE Annual Technical Conference and Exhibition, 27–29 October, Amsterdam, The Netherlands. SPE-170775-MS.
http://dx.doi.org/10.2118/170775-MS.

View all posts