An apparatus and method for connecting and selectively disconnecting within a wellbore first and second portions of a downhole tool string from each other. The apparatus may be a downhole tool having a first connector sub connectable with the first portion of the downhole tool string, a second connector sub connectable with the second portion of the downhole tool string, an internal chamber, and a fastener connecting the first and second connector subs. At least a portion of the fastener fluidly separates the internal chamber into a first chamber portion and a second chamber portion. The first chamber portion is fluidly connected with the space external to the downhole tool. The downhole tool is selectively operable to disconnect the first and second connector subs from each other to disconnect the first and second portions of the downhole tool string from each other.

An impact apparatus operable to be coupled along and impart an impact to a downhole tool string. The impact apparatus includes a housing, a first and second chambers within the housing, and a piston shaft assembly movable with respect to the housing. The piston shaft assembly includes a first piston slidably disposed within and dividing the first chamber into a first chamber portion and a second chamber portion, a first shaft connected with the first piston and axially movable into and out of the housing, a second piston slidably disposed within the second chamber, and a second shaft connecting the first and second pistons. The first chamber portion is open to a space external to the housing. The second chamber contains a fluid operable to maintain the piston shaft assembly and the housing in a predetermined relative position.

A downhole tool for connecting and selectively disconnecting within a wellbore first and second portions of a downhole tool string from each other. The downhole tool may include a first connector sub connectable with the first portion of the downhole tool string, a second connector sub connectable with the second portion of the downhole tool string, an internal chamber, and a fastener connecting the first and second connector subs. The fastener may fluidly separate the internal chamber into a first chamber portion and a second chamber portion. The first chamber portion may be fluidly connected with a space external to the downhole tool. The downhole tool may be selectively operable to disconnect the first and second connector subs from each other to disconnect the first and second portions of the downhole tool string from each other.

A pressure actuated jarring apparatus includes a tubular housing, a piston, a spring element, and a seat. The tubular housing has a passage therethrough extending from an upper end to a lower end. The piston is disposed within the central bore and is movable axially between an inactivated state and an activated state. The spring element is configured to store energy to drive the piston from the activated state. The seat is coupled to the piston such that when a plug is seated in an orifice of the seat fluid is prevented from flowing through the orifice. The jarring device is fired by increasing pressure in the passage until the plug is forced through the seat, thereby releasing the energy in the spring element and driving the piston from the activated state so that it impacts an abutment and generates a jarring force.

A fishing jar includes an outer housing, a mandrel positioned at least partially within the outer housing and having a fish end, an anvil coupled to or integral with the mandrel, a hammer coupled to or integral with the outer housing, and a triggering mechanism partitioning a first chamber and a second chamber, the first and second chambers separated axially apart and in fluid communication via the triggering mechanism. The triggering mechanism is configured to permit hydraulic fluid to flow from the first chamber to the second chamber at a first rate in response to pressing the outer housing to move toward the fish end of the mandrel during a downstroke of the outer housing, until the outer housing reaches a trigger position, and then permit the hydraulic fluid to flow from the first chamber to the second chamber at a second rate until the hammer impacts the anvil.

Apparatus and methods for creating a downhole impact. The apparatus may be an impact tool operable to be coupled between portions of a tool string conveyable within a wellbore extending into a subterranean formation. The impact tool may include a housing, a chamber within the housing, a piston slidably disposed within the chamber and dividing the chamber into a first chamber volume and a second chamber volume, and a shaft connected with the piston and axially movable with respect to the housing. The first chamber volume may be open to a space external to the housing and the second chamber volume may be fluidly isolated from the space external to the housing. The piston may be maintained in a predetermined position within the chamber to maintain pressure within the second chamber volume appreciably lower than pressure within the first chamber volume while the impact tool is conveyed along the wellbore.

A hydraulic jar coupled between opposing first and second portions of a downhole tool string. The hydraulic jar includes a housing comprising a shoulder protruding radially inward from an internal surface of the housing, a shaft disposed within the housing, a piston fixedly positioned about the shaft and fluidly sealed against the shoulder, and a pressure relief device. The housing and the shaft move axially relative to each other and the shoulder axially interposes first and second portions of an annulus formed between the shaft and the housing. The pressure relief device controls fluid flow from the first annulus portion to the second annulus portion based on a pressure of the fluid in the first annulus portion relative to a set pressure of the pressure relief device.

An apparatus and method for drilling is disclosed, including a drill string with at least one jar and one reaction valve. Drilling fluid flows through the reaction valve. The reaction valve is selectively throttled, which creates a differential pressure across the valve seat. The differential pressure creates an axial force that is transferred to the jar, which aids in cocking or firing the jar. In an embodiment, a reaction valve throttles downward fluid flow to create a downward compressional force on the jar, while in another embodiment, a reaction valve throttles upward fluid flow to create an upward tensile force on the jar. Upward and downward fluid flow may be alternatively throttled for alternately firing the jar upwards and downwards. A bypass valve may be included in the drill string for establishing a drilling fluid flow path when such may be otherwise obstructed by foreign matter in the wellbore.

A hydraulic jar comprising a housing and a mandrel slidably disposed in the housing forming an annular space therebetween. In an embodiment, the hydraulic jar comprises a flow control device fixedly connected to the mandrel and disposed in the annular space to divide the annular space into a first portion and a second portion. The flow control device comprises an annular member slidably positioned about the mandrel, wherein the annular member comprises a face, an inside surface, and an outside surface, wherein the outside surface of the annular member is disposed against an inside surface of the tubular housing, wherein the outer surface of the annular member and the inside surface of the tubular housing allow fluid flow therebetween at a first flow rate, wherein the inside surface of the annular member and the retaining surface of the retaining assembly allow fluid flow therebetween at a second flow rate.

A hydraulic jar coupled between opposing first and second portions of a downhole tool string. The hydraulic jar includes a housing comprising a shoulder protruding radially inward from an internal surface of the housing, a shaft disposed within the housing, a piston fixedly positioned about the shaft and fluidly sealed against the shoulder, and a pressure relief device. The housing and the shaft move axially relative to each other and the shoulder axially interposes first and second portions of an annulus formed between the shaft and the housing. The pressure relief device controls fluid flow from the first annulus portion to the second annulus portion based on a pressure of the fluid in the first annulus portion relative to a set pressure of the pressure relief device.