Zion Oil & Gas Inc (ZNOG)

[BlissBull]

Perforating multiple strings and thick cement

Concentric casing strings reduce the penetration of any perforating charge.[32][33] The thickness of the extra string of casing, as well as the thickness of the two sheaths of cement that must be penetrated, reduces the perforation penetration length. In severe cases of small liners set through larger pipe, such as 5-in. liner cemented in 9 5/8-in. casing, perforating both strings is considerably more difficult. For the best chance of perforating multiple strings, the largest, best designed deep-penetrating charge that can be run will generally have the best chance of penetrating through all the strings and into the formation.[23] Through-tubing guns are not recommended for shooting concentric strings because hole size and penetration are reduced with small charges.

http://petrowiki.org/Perforating_design#Perforating_multiple_strings_and_thick_cement