A system can include a disconnect tool connected as part of a tubular string, the disconnect tool including an outer housing, and an inner mandrel in the outer housing, in which an abrasive slurry is directed to flow through the tubular string and from the inner mandrel to an annulus between the inner mandrel and the outer housing, and the abrasive slurry erodes through the outer housing. A method can include installing a tubular string in a well, then deploying a disconnect assembly into the tubular string, and flowing an abrasive slurry through the disconnect assembly, thereby parting the tubular string. A disconnect tool can include a rotational flow structure configured to induce rotational flow, and an inner diameter decrease downstream of the rotational flow structure.

A system can include a disconnect tool connected as part of a tubular string, the disconnect tool including an outer housing, and an inner mandrel in the outer housing, in which an abrasive slurry is directed to flow through the tubular string and from the inner mandrel to an annulus between the inner mandrel and the outer housing, and the abrasive slurry erodes through the outer housing. A method can include installing a tubular string in a well, then deploying a disconnect assembly into the tubular string, and flowing an abrasive slurry through the disconnect assembly, thereby parting the tubular string. A disconnect tool can include a rotational flow structure configured to induce rotational flow, and an inner diameter decrease downstream of the rotational flow structure.

A downhole tool, for removing a restriction in a well tubular metal structure having a wall and an inner diameter, has a tool axis and a tool body having a first part and a second part, an electrical motor arranged in the first part for rotating a rotatable shaft, and a core bit arranged in the second part and having a first end connected with the rotatable shaft and a second end having a cutting edge. The second part of the downhole tool further includes a locator for locating the rim section, the locator being rotable with the core bit until the locator locates the rim section and a threshold value is reached.

A downhole tool, for removing a restriction in a well tubular metal structure having a wall and an inner diameter, has a tool axis and a tool body having a first part and a second part, an electrical motor arranged in the first part for rotating a rotatable shaft, and a core bit arranged in the second part and having a first end connected with the rotatable shaft and a second end having a cutting edge. The second part of the downhole tool further includes a locator for locating the rim section, the locator being rotable with the core bit until the locator locates the rim section and a threshold value is reached.

A fracbot for fracturing a formation includes a drill bit; a rotary swivel configured to rotate the drill bit; a motor; a battery; and a coating encompassing the fracbot. The motor is configured to induce vibrations that create a spiral movement of the fracbot. The spiral movement of the fracbot allows the fracbot to traverse existing fractures in the formation including a first fracture and a second fracture. The battery is configured to power the fracbot. The coating is configured to dissolve at a predefined temperature. The fracbot is configured to create a channel that connects the first fracture and the second fracture.

A fracbot for fracturing a formation includes a drill bit; a rotary swivel configured to rotate the drill bit; a motor; a battery; and a coating encompassing the fracbot. The motor is configured to induce vibrations that create a spiral movement of the fracbot. The spiral movement of the fracbot allows the fracbot to traverse existing fractures in the formation including a first fracture and a second fracture. The battery is configured to power the fracbot. The coating is configured to dissolve at a predefined temperature. The fracbot is configured to create a channel that connects the first fracture and the second fracture.

A system can include a disconnect tool connected as part of a tubular string, the disconnect tool including an outer housing, and an inner mandrel in the outer housing, in which an abrasive slurry is directed to flow through the tubular string and from the inner mandrel to an annulus between the inner mandrel and the outer housing, and the abrasive slurry erodes through the outer housing. A method can include installing a tubular string in a well, then deploying a disconnect assembly into the tubular string, and flowing an abrasive slurry through the disconnect assembly, thereby parting the tubular string. A disconnect tool can include a rotational flow structure configured to induce rotational flow, and an inner diameter decrease downstream of the rotational flow structure.

A system can include a disconnect tool connected as part of a tubular string, the disconnect tool including an outer housing, and an inner mandrel in the outer housing, in which an abrasive slurry is directed to flow through the tubular string and from the inner mandrel to an annulus between the inner mandrel and the outer housing, and the abrasive slurry erodes through the outer housing. A method can include installing a tubular string in a well, then deploying a disconnect assembly into the tubular string, and flowing an abrasive slurry through the disconnect assembly, thereby parting the tubular string. A disconnect tool can include a rotational flow structure configured to induce rotational flow, and an inner diameter decrease downstream of the rotational flow structure.

A downhole device delivery and drive transfer system includes a sub which is arranged to attach to a drill string and a tool which is configured to enable it to travel through the drill string and releasably couple to the sub. The sub and the tool are arranged so that when they are releasably coupled to each other torque imparted to the drill string is transferred by the sub to the tool. The tool is arranged to carry one or more devices for performing one or more downhole functions such as core drilling, hole reaming or wedge placement for directional drilling. The system also has a guide mechanism that operates between the sub and the tool to guide the tool to a known rotational orientation relative to the sub as the tool travels into the sub. A fluid control system controls the flow of fluid through the tool through a downhole outlet and a plurality of ports intermediate opposite ends of the tool.

A system and method for installing casing in a blind horizontal well for blind horizontal directional borings. The system and method may include an example of an offset transmitter sonde assembly that contains an open central passage through which well casing can be inserted, and an example of a drill bit assembly that may be remotely uncoupled from a drill string, leaving the bit in the bore created. Remote uncoupling of the drill bit assembly tends to allow a casing to be installed in the bore while the drill string and bit remain in the bore for support during casing installation. After installation of the casing the drill bit assembly may be uncoupled from the drill string, allowing the drill string to be withdrawn from the bore, with the drill bit assembly remaining in the bore.