1. n. [Perforating]

The hole created in the internal surface of the casing or liner by the perforating charge or bullet. The entrance hole should be clean, free from burrs and round to create an efficient flow path between the reservoir and wellbore. Depending on gun size and standoff, the entrance hole is typically between 3/8- and 1/2-in in diameter. The perforation charge design generally is optimized to provide maximum penetration while achieving a medium-size entrance hole. Special charge designs can be used when optimizing the entrance hole size is important, as in sand-control applications.

See: big hole charge,  sand control