Full Dissolvable Frac Plug for High-Temperature Wellbores
Authors: Norman Tyler , Walton Zachary , Fripp Michael 
Published: April 2018

Dissolvable frac plugs are used for hydraulic fracturing applications. However, most new dissolvable materials exhibit limited strength and accelerated degradation in high-temperature formations. A new high-temperature dissolvable frac plug was developed for such high-temperature formations, where wellbore temperatures generally exceed 250°F. This new dissolvable frac plug is composed of a high-strength metal with an elastomeric seal that dissolves completely in higher-temperature wellbore fluids.

Traditional frac plugs are constructed from composite materials and nondissolving elastomers. These nondissolving frac plugs obstruct production and need to be milled out after fracturing is completed. Dissolvable frac plugs dissolve in wellbore fluid, eliminating the need for a separate mill run intervention into the wellbore. However, the dissolution process of the metal and elastomer accelerates in higher-temperature shale formations. As dissolution occurs, material strength and elastomer integrity decreases. Therefore, a high-strength dissolvable metal and elastomer was developed to create a frac plug capable of providing effective zonal isolation while fully dissolving in high-temperature formations.

The new high-temperature frac plug is optimized for use with the fluids used and temperatures experienced in Middle Eastern basins. Comprehensive laboratory testing was conducted on the dissolvable metal alloy and dissolvable elastomer for the new high-temperature dissolvable frac plug. During laboratory testing, the dissolution performance of the high-temperature frac plug was optimized by increasing the material dopant for select, noncritical components of the frac plug. Metallographic analysis illustrates the effect of the dopant on the dissolution of the metallic alloy and how accelerated dissolution for select components can reduce the time required for full dissolution of the frac plug. The dissolvable elastomer uses a hydrolytic degradation reaction that is suitable for high-temperature fluids.

Temperature modeling was conducted to predict wellbore temperature over the duration of the pumping and treatment schedules for certain wells in the Middle East region. Based on these models, a second high-temperature frac plug option was developed to optimize the dissolution performance in such wells by increasing the material dopant for additional frac plug components. The result is two high-strength frac plugs that can be set anywhere within the wellbore and dissolve completely in high-temperature formations. The high-strength dissolvable materials allow dissolution in water-based wellbore fluid, formation fluid, or production fluid.

The novel frac plug is designed for high-temperature plug-and-perf applications and is composed of high-strength engineered materials. Complete dissolution of the frac plug eliminates the need for a separate mill run intervention into the wellbore, which reduces cost, operation time, and risk to personnel. This paper discusses the development of the dissolvable elastomer, the tested behavior of the high-temperature dissolvable frac plug, and the use of wellbore modeling to further optimize the performance of the high-temperature dissolvable frac plugs.