A drive sub for a drilling assembly includes a tubular body configured to receive and releasably engage a drilling tool. The body has inner and outer faces and further has a castellated edge provided on its operative downhole end, which edge defines a plurality of lugs separated from each other by intervening slots. In one aspect the drive sub has a contour profile provided at least in partially along a circumference of the castellated edge, wherein the contour profile traverses the castellated edge substantially from the inner face to the outer face. In another aspect the drive sub has a channel provided in each of the lugs, wherein the channel at least partially traverses the lugs and leads from an inlet opening on the castellated edge to an outlet opening on the outer face. The contour profile and/or channel facilitate flow of drilling fluid and cuttings past the lugs during use.

Bottom hole assemblies for drilling through a lost circulation zone of a wellbore includes a drill string, a drill bit and a cladding seat coupled to the drill string, an expandable cladding sheath engaged with the cladding seat, a release mechanism coupling an uphole end of the expandable cladding sheath to the drill string, and an expander translatable axially along the drill string. The expandable cladding sheath is a fiber reinforced polymer. The cladding seat releasably couples a downhole end of the expandable cladding sheath to the drill string, and the release mechanism operates to release the uphole end of the expandable cladding sheath from the drill string. The expander deforms the expandable cladding sheath outward into contact with a wall of a wellbore when translated axially through a central cavity of the expandable cladding sheath. The bottom hole assembly may enable drilling ahead through a lost circulation zone.

Bottom hole assemblies for drilling through a lost circulation zone of a wellbore includes a drill string, a drill bit and a cladding seat coupled to the drill string, an expandable cladding sheath engaged with the cladding seat, a release mechanism coupling an uphole end of the expandable cladding sheath to the drill string, and an expander translatable axially along the drill string. The expandable cladding sheath is a fiber reinforced polymer. The cladding seat releasably couples a downhole end of the expandable cladding sheath to the drill string, and the release mechanism operates to release the uphole end of the expandable cladding sheath from the drill string. The expander deforms the expandable cladding sheath outward into contact with a wall of a wellbore when translated axially through a central cavity of the expandable cladding sheath. The bottom hole assembly may enable drilling ahead through a lost circulation zone.

An interchangeable casing shoe for a wellbore is disclosed. The interchangeable casing shoe includes a cylindrical housing, a first engagement assembly mounted to an outer diameter of the cylindrical housing and selectively extendible between a recessed position and an extended position, and a second engagement assembly mounted within the cylindrical housing and configured to engage a running tool. The wellbore has a wellbore tubular having an internal diameter surface. When in the extended position, the first engagement assembly engages the internal diameter surface of the wellbore tubular. When deployed at depth in the wellbore, the running tool engages the second engagement assembly and selectively shifts the first engagement assembly into the recessed position releasing the casing shoe.

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 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.

The present invention relates to a downhole tool for removing a restriction in a well tubular metal structure having a wall and an inner diameter, the restriction partly blocking the inner diameter, creating an opening defined at least partly by a rim section of the restriction, the downhole tool having a tool axis and comprising a tool body having a first part and a second part, an electrical motor arranged in the first part for rotating a rotatable shaft, 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, wherein the second part of the downhole tool further comprises a locator for locating the rim section, a collecting means for collecting part of the restriction to be cut out by the cutting edge, the locator and the collecting means are rotating with the core bit until the locator locates the rim section and a threshold value is reached.

The present invention relates to a downhole tool for removing a restriction in a well tubular metal structure having a wall and an inner diameter, the restriction partly blocking the inner diameter, creating an opening defined at least partly by a rim section of the restriction, the downhole tool having a tool axis and comprising a tool body having a first part and a second part, an electrical motor arranged in the first part for rotating a rotatable shaft, 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, wherein the second part of the downhole tool further comprises a locator for locating the rim section, a collecting means for collecting part of the restriction to be cut out by the cutting edge, the locator and the collecting means are rotating with the core bit until the locator locates the rim section and a threshold value is reached.

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.