Case Study: Plug Your Way Through Downhole Restrictions
Casing deformations are common in the south-west shale regions of China and the Middle East, where the widespread use of 5.5-in., 26- and 26.8-lb/ft casing is the norm. In these regions, the majority of frac plugs are designed with an outer diameter (OD) of 4.055 in. or slightly larger, which frequently encounter restrictions resulting in the loss of bottomhole assemblies downhole. Frac plugs were designed with reduced ODs intended to bridge the gap between normal- and smaller-OD plugs for stage isolation.
Unable to successfully deploy plug-and-perf bottomhole assemblies (BHA) to the desired depth has resulted in significant nonproductive time (NPT) in unconventional completions. These instances of NPT are primarily attributed to casing deformation, rather than plug presets.
To address these downhole restrictions, frac plugs with smaller outer diameters (OD) were introduced for stage isolation. This reduction in plug OD minimizes the risk of getting stuck in tight spaces, but it also compromises pressure ratings. This raises the risk of skidding (slip losses, anchoring) and leads to increased fluid usage for pumpdown.
These challenges not only risk well productivity, but also escalate completion time and costs.