having a permeability lower than that of the virgin formation matrix may be formed around perforation tunnels the process may also generate a tunnel full of rock debris mixed in with the perforator charge debris the extent of the damage and the amount of loose debris in the tunnel may be dictated by a variety of factors including formation properties explosive charge properties pressure conditions fluid properties and so forth the shock damaged region and loose debris in the perforation tunnels may impair the productivity of production wells or the injectivity of injector wells one method for obtaining clean perforations involves underbalanced perforating the perforation is carried out with a lower wellbore pressure than the formation pressure the pressure equalization can be achieved by fluid flow from the formation and into the wellbore this can be caused by flow into the perforating gun housing this fluid flow carries some of the damaging rock particles away from the perforations and improves permeability it should be noted that the underbalance operation can be carried out after perforation and without charges that perforate the casing or the formation the present application includes embodiments including dynamic underbalance in a defined interval of a well bore using a pressure wave to create a transient plug these.