Dissolvable Metal vs. Dissolvable Plastic in Downhole Hydraulic Fracturing Applications

Abstract

Multiple dissolvable materials are becoming available in the energy industry. While dissolvable plastics have their applications, a dissolvable metal has distinct advantages over a dissolvable plastic for hydraulic fracturing. Multiple tests were performed to compare the characteristics of dissolvable metals and dissolvable plastics. The two product families that were explored were dissolvable frac balls and dissolvable frac plugs. For direct comparison, frac balls and frac plugs were constructed using a dissolvable metal and dissolvable plastic. For both dissolvable frac balls, the materials were tested for impact resistance. For both dissolvable frac plugs, the materials were pressure tested. The dissolvable metal frac ball provided higher impact resistance than the dissolvable plastic frac ball. The dissolvable metal frac ball survived impact at 19 bbl/min on ball-to-seat interference as small as 0.035 in. When the same test was performed using a dissolvable plastic ball, the ball shattered and passed through the seat. The seat overlap needed to be increased to 0.125 in. before the dissolvable plastic ball was able to consistently survive impact against the seat. For the frac plugs, the dissolvable plastic was unable to be used as a bottom slip because of the anchoring loads generated while the plug sealed against differential pressure. The dissolvable metal was able to anchor these loads when used as the material for the bottom slip. For a dissolvable plastic mandrel to survive the setting loads, it had to be set in compression. The dissolvable metal mandrel had no issue being set in tension, allowing for the operational setting procedures to be unchanged. Dissolvable plastic also required the inner diameter of the frac plug to be much smaller. Using dissolvable metal instead of dissolvable plastic reduces design requirements for converting non-dissolvable downhole tools to dissolvable ones. Dissolvable metal provides an increased impact resistance, has no issues being set under tension, and allows for using smaller ball-to-seat overlaps, all of which provide more flexibility for use in industry applications.