A technique facilitates controlled creation of pressure waves in a downhole environment. The technique enables creation of, for example, dynamic underbalance (DUB) pressure waves or dynamic overbalance (DOB) pressure waves which can be used to perform desired activities downhole. According to an embodiment, a pump is coupled with a pressure chamber and conveyed downhole into a borehole to a desired location. The pump may be operated downhole to change a pressure level in the pressure chamber until a sufficient pressure differential exists between an interior and an exterior of the pressure chamber. A release mechanism in communication with the pressure chamber is then rapidly opened to establish the desired pressure wave as the differing pressures equalize.

A technique facilitates controlled creation of pressure waves in a downhole environment. The technique enables creation of, for example, dynamic underbalance (DUB) pressure waves or dynamic overbalance (DOB) pressure waves which can be used to perform desired activities downhole. According to an embodiment, a pump is coupled with a pressure chamber and conveyed downhole into a borehole to a desired location. The pump may be operated downhole to change a pressure level in the pressure chamber until a sufficient pressure differential exists between an interior and an exterior of the pressure chamber. A release mechanism in communication with the pressure chamber is then rapidly opened to establish the desired pressure wave as the differing pressures equalize.

Provided is an downhole actuation mechanism, the actuation mechanism comprising: a first part having a guiding surface; a second part defining a passageway; the second part being movable with respect to the guiding surface between a first position and a second position; the second part defining a first clearance of the passageway in the first position; the second part defining a second clearance of the passageway in the second position, the second clearance being larger than the first clearance.

A mill including a housing having a fluid bypass pathway, a milling feature at a longitudinal end of the housing, a chamber defined by the housing, and a piston disposed in communication with the chamber, the piston defining a fluid passageway initially aligned with the fluid bypass pathway, the piston responsive to pump pressure to move toward the milling feature, the movement misaligning the fluid passageway with the fluid bypass pathway.

A frac dart includes a body having an outer surface and an end including at least one opening. A cutter support is mounted at the end adjacent the at least one opening. A cutter is moveably mounted at the cutter support. A counter support is slideably mounted on the outer surface, and a counter is arranged between the counter support and the cutter support. The cutter is operable to sever a portion of the counter.

A plug assembly includes an expandable assembly, a locking ring and a cup. The expandable assembly is adapted to be deformed radially over the locking ring and the cup. The locking ring has a stopping inner surface. The plug assembly is used with one or more untethered objects, the untethered objects having an outer surface adapted to couple with the cup, and the cup having an outer surface adapted to couple with the stopping inner surface of the locking ring. The combination of cup and untethered objects is also adapted to contact an inner surface of the plug assembly and, using well fluid pressure, to apply forces to the plug assembly. The forces cause the longitudinal movement of the cup and untethered objects while contacting the inner surface of the plug assembly until the cup contacts the stopping inner surface of the locking ring.

A liner string for a wellbore includes a liner hanger assembly (LHA) and a liner hanger deployment assembly (LHDA) releasably attached to the LHA. The LHDA includes a central bore and a running tool moveable from a locked position to an unlocked position, the running tool including a flow path in communication with the central bore. The liner string further includes a chamber disposed between the LHDA and LHA, wherein the chamber is in selective fluid communication with the flow path. Wherein, when the flow path is closed, the chamber is isolated from the central bore, and when the flow path is open, the flow path provides fluid communication between central bore and chamber.

A liner string for a wellbore includes a liner hanger assembly (LHA) and a liner hanger deployment assembly (LHDA) releasably attached to the LHA. The LHDA includes a central bore and a running tool moveable from a locked position to an unlocked position, the running tool including a flow path in communication with the central bore. The liner string further includes a chamber disposed between the LHDA and LHA, wherein the chamber is in selective fluid communication with the flow path. Wherein, when the flow path is closed, the chamber is isolated from the central bore, and when the flow path is open, the flow path provides fluid communication between central bore and chamber.

A plug assembly for a cementing operation in a well includes a bottom wiper plug configured to land in or near the toe of a well and receive a cement slurry therethrough, a top wiper plug releasably coupled to the bottom wiper plug and configured to land on the bottom wiper plug after the cement slurry is received through the bottom wiper plug, a bridge plug coupled to the top wiper plug and configured to move toward the bottom wiper plug with the top wiper plug after the bottom wiper plug is landed in or near the toe of the well, and a sensor sub coupled to the bridge plug and configured to detect a gate in the well.

A tool for cleaning out the lower end of a cased wellbore having an installed production string. The tool is lowered down the production string until it projects from an end of the production string and into the wellbore. High pressure fluid is then sprayed from the tool's fluid openings into nearby portions of the wellbore. Once cleaning operations are complete, the tool is carried back to the ground surface using subterranean fluid pressure.