An example underbalance pressure generator device includes a housing having a first end, a second end, and an implosion chamber between the first and second ends, one or more influx ports defined in the housing and enabling fluid communication between the implosion chamber and an exterior of the housing, at least one frangible member fixedly attached to the housing such that a pressure differential can be generated across the at least one frangible member between the implosion chamber and the exterior of the housing, and an actuation device within the housing and configured to rupture the at least one frangible member upon being triggered.