US Patent 9605514 Using dynamic underbalance to increase well productivity

An underbalance pressure generator includes a housing having a first end and a second end and defines a piston chamber that extends between the first and second ends. A piston is movably arranged within the piston chamber, and one or more influx ports are defined in the housing at or near the second to enable fluid communication between the piston chamber and an exterior of the housing. A locking mechanism is arranged at or near the second end and capable of securing the piston at or near the second end.