Case Study: China Field Test of Dissolvable Collet Demonstrates Time and Cost Savings

Abstract

_ Over the past few years, dissolvable frac plugs have been effective in addressing unconventional completion challenges by reducing the need for intervention and decreasing overall completion time and cost. However, the majority of dissolvable frac plugs on the market are made up of complex components, which increase their likelihood of failing when run in hole, during stimulation, or not fully dissolving before cleanout. This has resulted in skepticism and challenges with the older generation of dissolvable plugs. To address these issues, Vertechs introduced a new dissolvable collet that can withstand high and low temperatures (100–350°F), has a pressure rating of 10,000 psi, and is less than 2.5 in. in length (Fig. 1). The dissolvable collet combines anchoring and sealing functions into a single component using high-expansion dissolvable metal to create a collet structure with slip segments and a metal seal ring, eliminating the need for elastomers as a sealing material. Compared to traditional frac plug designs, the collet design is simpler and more robust, enabling it to be run and pumped down at higher speed, eliminating issues accompanied with high annular velocities, thereby increasing its running speed in the wellbore. Since it uses less material for manufacturing, it is lighter and easier to dissolve than traditional frac plugs; for instance, the collet only weighs around 1.1 lb, which results in faster cleanout runs, allowing the operators to produce their wells sooner. Many traditional frac plugs weigh around 11–13 lb. Field Test Results An operator in China conducted a field test on a four-well pad in an onshore, southwest shale formation using traditional dissolvable frac plugs in two wells and the new dissolvable collets in the other two. The goal was to speed up completion and minimize coiled tubing operation spending. The results for plug-and-perf and cleanout runs were compared between the two types of plugs, and the new design showed significant improvements. When running conventional frac plugs into the wellbore, the wireline crew adhered to the line speed chart provided by the tool suppliers to minimize the impact of annular velocity on the elastomers. To achieve this, the running speed was maintained within a certain limit. Consequently, the average running time per stage in the vertical section was approximately 50 minutes, while the pumpdown time was about 30 minutes per stage in the horizontal section. In contrast, the dissolvable collets were deployed and pumped down at a higher speed due to their uncomplicated and sturdy structure, leading to an average running time of 32 minutes per stage in the vertical section and 19 minutes per stage in the horizontal section. While it is true that the pumpdown time in the horizontal section decreases as the stages move from the toe to the heel, the average time per stage is used for easy comprehension and visualization. When combined with other aspects of the plug-and-perf process, such as setting the plug, perforating, and pull out of hole, it became apparent that significant time savings were achieved during the running and pumpdown phases in both the vertical and horizontal sections of the well. This resulted in a 15% reduction in time spent per stage (Fig. 2).