A system used to dislodge and, if necessary, sever a tubular string that is stuck within a cased wellbore. The system utilizes a jar, a plurality of plugs, and a tubular severance device. Components of the system are carried to their respective desired downhole positions by downward fluid flow within the wellbore. The jar is configured to jar the string in an effort to dislodge the string from its stuck point. The plugs are configured to fill open perforations formed in the casing in order to direct the fluid toward the stuck point and away from the perforations. If the string cannot be freed by the jar, the tubular severance device is deployed within the string above the stuck point. Detonation of the device severs the string above the stuck point.

A jarring tool includes a spring and a hydraulic piston cylinder arrangement for controlling the release of a mandrel to initiate a jarring force. The tool includes an adjustment mechanism for adjusting the minimum amount of an upward pulling force required to release the mandrel. The adjustment mechanism includes an axially adjustable trigger sleeve that cooperates with a dog clutch surrounding the mandrel.

A jarring tool includes a spring and a hydraulic piston cylinder arrangement for controlling the release of a mandrel to initiate a jarring force. The tool includes an adjustment mechanism for adjusting the minimum amount of an upward pulling force required to release the mandrel. The adjustment mechanism includes an axially adjustable trigger sleeve that cooperates with a dog clutch surrounding the mandrel.

A jarring tool can include a longitudinally displaceable piston, a first fluid chamber having a volume that decreases in response to displacement of the piston, a flow controller that controls flow of fluid between the first fluid chamber and a second fluid chamber, and a plug seat secured to the piston. A method of applying a jarring force can include applying a pressure differential across a plug in a jarring tool, the plug restricting flow from a first flow passage section to a second flow passage section, then increasing a flow rate of fluid from the first flow passage section. Another jarring tool can include an outer housing with a longitudinal flow passage and seal surfaces at opposite ends of the outer housing, and a flow obstruction, fluid flow through the flow passage being increased in response to application of a pressure differential across the obstruction.

A jarring tool can include a longitudinally displaceable piston, a first fluid chamber having a volume that decreases in response to displacement of the piston, a flow controller that controls flow of fluid between the first fluid chamber and a second fluid chamber, and a plug seat secured to the piston. A method of applying a jarring force can include applying a pressure differential across a plug in a jarring tool, the plug restricting flow from a first flow passage section to a second flow passage section, then increasing a flow rate of fluid from the first flow passage section. Another jarring tool can include an outer housing with a longitudinal flow passage and seal surfaces at opposite ends of the outer housing, and a flow obstruction, fluid flow through the flow passage being increased in response to application of a pressure differential across the obstruction.

A smart jarring system for freeing stuck equipment downhole is disclosed. The smart jarring system comprises a set of jars, at least one laser source and at least one laser receiver that corresponds to the at least one laser source. The laser receiver intercepts a laser beam that is emitted from the laser source. This interception helps determine when the set of jars fired and in which direction the set of jars fired. The smart jarring system further comprises one or more sensors selected from the group consisting of vibration sensors, temperature sensors, and torque/tensile sensors. These sensors are configured to diagnose downhole conditions and help free the stuck equipment downhole.

A smart jarring system for freeing stuck equipment downhole is disclosed. The smart jarring system comprises a set of jars, at least one laser source and at least one laser receiver that corresponds to the at least one laser source. The laser receiver intercepts a laser beam that is emitted from the laser source. This interception helps determine when the set of jars fired and in which direction the set of jars fired. The smart jarring system further comprises one or more sensors selected from the group consisting of vibration sensors, temperature sensors, and torque/tensile sensors. These sensors are configured to diagnose downhole conditions and help free the stuck equipment downhole.

A hydraulic jar includes a tubular housing having central bore and an exterior. The housing includes a passage from the central bore to the exterior. A mandrel is axially movable within the housing, forming an annular space between the mandrel and the housing that includes a timing fluid. The mandrel includes an interior axial space that permits the flow of a drilling fluid. A timing device is fixed to the mandrel in the annular space. A trigger is capable of blocking the flow of drilling fluid through the axial space in the mandrel, and the mandrel moves axially in the housing when the trigger engages the mandrel. The timing device causes the mandrel to move at a first speed and at a second speed to create the impulse. The drilling fluid exits the central bore through the opening after the mandrel moves past the opening.

A hydraulic jar includes a tubular housing having central bore and an exterior. The housing includes a passage from the central bore to the exterior. A mandrel is axially movable within the housing, forming an annular space between the mandrel and the housing that includes a timing fluid. The mandrel includes an interior axial space that permits the flow of a drilling fluid. A timing device is fixed to the mandrel in the annular space. A trigger is capable of blocking the flow of drilling fluid through the axial space in the mandrel, and the mandrel moves axially in the housing when the trigger engages the mandrel. The timing device causes the mandrel to move at a first speed and at a second speed to create the impulse. The drilling fluid exits the central bore through the opening after the mandrel moves past the opening.

A release mechanism for a jarring tool is formed by a plurality of segmented release lugs. Each lug includes a plurality of axial spaced projections on an inner surface and a plurality of grooves on an outer surface. The projections have either different widths or are separated by varying distances and releaseably engage corresponding grooves in a mandrel located within a housing of the tool. The release lugs are positioned between a trigger sleeve and the mandrel.