A downhole impact apparatus operable to impart an impact to an object within a wellbore. The impact apparatus may include a housing, a first chamber within the housing, a second chamber within the housing, and a piston assembly slidably disposed within the housing. The piston assembly may include a first piston slidably disposed within the first chamber and dividing the first chamber into a first volume and a second volume, a second piston slidably disposed within the second chamber, and a shaft connecting the first and second pistons. The first volume may be open to a space external to the housing and the second volume may be fluidly isolated from the space external to the housing. Relative movement between the piston assembly and the housing ends with the impact. The second chamber may be configured to contain a fluid to prevent relative movement between the piston assembly and the housing.

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 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.

An assembly, method and device are for performing a survey of tubing which is stuck in a borehole. The assembly has a tractor for advancing the assembly along the tubing on an inside thereof; at least one engager connected to the tractor, the engager being configured to couple the assembly to a wall of the tubing, such that a stimulus applied to the tubing, e.g. components of force or manipulation of the tubing, can be communicated to produce a response in a part of the assembly. A detector may detect the response when the assembly is coupled to the wall of the tubing, in order to produce data based on the response for determining a location at which the tubing may, or may not, be subjected to at least one operation for freeing the string or a portion thereof.

A mini-severing and back-off tool includes a tubular magazine for a column of explosive pellets that are sized in diameter to provide a predetermined weight of explosive per unit column length. The tubular wall is vented at prescribed intervals for fluid pressure equalization between the internal bore of the tubular and the fluid pressure around the outside of the tubular. A fluid barrier is positioned between one end of the explosive pellet tubular and a detonator or an explosive booster provided to detonate the explosive pellet tubular. The explosive pellet tubular is positioned within the flow bore of a pipe string and adjacent to an intended pipe joint, and the explosive pellet tubular is detonated simultaneously with an application of torque on the pipe string, wherein the torque is applied in the thread release direction to disassemble the intended pipe joint.

A downhole impact apparatus operable to impart an impact to an object within a wellbore. The impact apparatus may include a housing, a first chamber within the housing, a second chamber within the housing, and a piston assembly slidably disposed within the housing. The piston assembly may include a first piston slidably disposed within the first chamber and dividing the first chamber into a first volume and a second volume, a second piston slidably disposed within the second chamber, and a shaft connecting the first and second pistons. The first volume may be open to a space external to the housing and the second volume may be fluidly isolated from the space external to the housing. Relative movement between the piston assembly and the housing ends with the impact. The second chamber may be configured to contain a fluid to prevent relative movement between the piston assembly and the housing.

A back-off tool comprises a magazine cylinder having one distal end of a long mast rod secured to the lower end-face of a magazine cylinder. The magazine cylinder is attached to an electrically detonated firing head. A first plurality of blind hole cavities penetrate the magazine cylinder end-face around the mast rod junction. A second plurality of elongated detonation cord ends are inserted into high temperature grease filled magazine cylinder cavities. From the cavities, the detonation cord lengths are bound to the rod surface along the rod length by non-metallic cord. The tool assembly is secured to the end of a wireline or tubing string for downhole placement and detonation.

A downhole assembly includes a matrix material and a unit in contact with the matrix material. The unit includes a core having an energetic material, an activator disposed in direct contact with the core, and at least one layer disposed on the core. The activator includes a triggering system having an igniter and a pre-set timer connected in an electrical circuit. The igniter is inactive in an open condition of the electrical circuit, and, after a pre-set time period, the pre-set timer closes the electrical circuit and the igniter is activated.

A downhole assembly includes a downhole tool including a degradable-on-demand material including: a matrix material; and, a unit in contact with the matrix material. The unit includes a core including an energetic material configured to generate energy upon activation to facilitate degradation of the downhole tool; and, an activator disposed in contact with the core, the activator including a triggering system having an electrical circuit and an igniter within the electrical circuit, the electrical circuit having an open condition and a closed condition, the electrical circuit configured to be in the closed condition after movement of an object downhole that engages directly or indirectly with the triggering system, and the igniter arranged to ignite the energetic material in the closed condition of the electrical circuit. In the open condition of the electrical circuit the igniter is inactive, and in the closed condition of the electrical circuit the igniter is activated.

A mini-severing and back-off tool includes a tubular magazine for a column of explosive pellets that are sized in diameter to provide a predetermined weight of explosive per unit column length. The tubular wall is vented at prescribed intervals for fluid pressure equalization between the internal bore of the tubular and the fluid pressure around the outside of the tubular. A fluid barrier is positioned between one end of the explosive pellet tubular and a detonator or an explosive booster provided to detonate the explosive pellet tubular. The explosive pellet tubular is positioned within the flow bore of a pipe string and adjacent to an intended pipe joint, and the explosive pellet tubular is detonated simultaneously with an application of torque on the pipe string, wherein the torque is applied in the thread release direction to disassemble the intended pipe joint.