Plugs can hold pressure perfectly in lab tests, but might have issue in live wells. Although every supplier's lab tests are extremely strict, however, there are some factors that are dificult to simulate.
When pumping down in the horizontal section, the plug is in contact with the bottom of the casing wall. But in most plug and perf animations, the tool string is centralized in the casing, and traveling smoothly like magnetic levitated train. Inreal life, it is more like being dragged by a horse on a rough road with your face downwards.
We have retrieved plugs that couldn't be pumped down to the setting depth due to downhole restriction, there were a lot of scratches and dents on the surface of the plug, indicating the plug was not only been dragged, it was also bumping a lot, which is very likely to cause damage the slips, that could lead to a pre-set, or bad anchor.
To minimize these risks and improve robustness, we enhanced gauge protection, making sure the slip buttons are well protected by the plug OD. A specialized impact test device was also developed to evaluate the robustness and integrity of our frac plugs when obstacles are encountered while pumping down at high speed. Every new design must go through the impact test at maximum speed of 955ft/min.