A bearing assembly for a downhole mud motor has a transitional radial support in the form of a transitionally tapered bearing mandrel. The new radial support includes a generally cylindrical bearing housing having an upper end facing upstream in the direction of the drill string and a lower end, an outer cylindrical surface and an inner cylindrical surface, and wherein a portion of the inner cylindrical surface surrounds and contains a plurality of axial bearings. The bearing mandrel underlies the bearing housing and has an outer surface which defines a lower bearing region. The lower bearing region including a series of stepped outer diameter regions that also define a transitional reduction in cross-section area for the lower bearing region of the mandrel which, in turn, allows the bearing mandrel to have a progressive reduction in bending strength and to become a more active element in bending strength of the mud motor, instead of relying primarily upon the bearing housing.

An interlocking independent tubular with multiple circumferential sections allows a borehole to advance by encasing with a single pass, the structurally independent tubular. The independent tubular is single layered, having a major arc and a minor arc forming circumferential sections. The minor arc may be defined by less than 180 degrees, and the major arc may be a circumferential section defined by greater than 180 degrees. The major arc and minor arc align longitudinally to form the independent tubular. Installation may involve partially radially collapsing the major arc, inserting the major arc and minor arc through a previously installed tubular, reexpanding the major arc and connecting the major arc and minor arc to form the independent tubular downhole from the previously installed tubular, and joining the independent tubular to the previously installed tubular. The tubes may be joined by interlocking female and male ends of the tubes.

A system and method are used in drilling a borehole in a formation. A trip to move a drillstring in the borehole is identified, where the trip is expected to produce a piston effect that changes a downhole pressure of the fluid in the borehole. A peak speed to move the drillstring in the borehole is calculated for the trip, and adjustments to a surface backpressure of the drilling system is calculated for the trip at the calculated peak speed to keep the downhole pressure within a tolerance of the formation. The drillstring is moved in the trip according to the calculated peak speed, and the downhole pressure change produced by the piston effect is counteracted by automatically adjusting the surface backpressure according to the calculated adjustments.

A system and method for casing drilling with a subsea casing drive adapted to engage at the outer circumference of the casing string, to impart a linear force and/or torque to the casing string, and such a subsea casing drive per se are disclosed. During drilling, the subsea casing drive is provided in a subsea unit further comprising a blowout preventer, a pressure control device and a mud pump with an outlet to a mud hose connectable to a surface vessel. The wellbore is drilled by driving the bottom hold assembly, BHA, and the casing string into the wellbore by the subsea casing drive, while discharging mud and cuttings via the mud hose and supplying mud to the BHA from the mud circulation system on the vessel via the landing string and casing string.

A constant velocity joint for downhole power transmission has a first insert mounted in a radially extending drive shaft arm. The first insert engages a second insert mounted along a slot formed in a tubular housing disposed to receive the arm. The material for the two inserts may be different, having different galling properties. An insert may be shaped to have at least a flat surface, a cylindrical surface intersecting the flat surface, and a conical surface intersecting the cylindrical surface. The inserts may extend beyond the cavities in which they are mounted. Opposing cavity walls adjacent the cavity opening may be angled away from one another to permit the insert to flex under a load. The back wall of a cavity and back surface of an insert may be arcuate to permit rotational movement of the insert under a load.

An apparatus for driving a drillable drill bit of a drilling assembly and a method of manufacturing of the apparatus for driving the drillable drill bit is provided. The apparatus employs a drilling assembly that includes one of a casing string or a tubular string suspendable in a borehole and a drill pipe housed within one of the casing string or the tubular string. The drillable drill bit is fixed at the bottom of the drill pipe. The drilling assembly further includes a plurality of motors mounted circumferentially on the one of casing string or tubular string, wherein the plurality of motors is attached to wall of the one of casing string or tubular string and are partially outside the one of casing string or tubular string in the borehole, and the plurality of motors are configured to drive the drillable drill bit.

An arrangement and a method for installing a casing in a borehole are described. The arrangement includes a casing, a boring pipe, which is adapted within the casing, and the boring pipe includes flow channels for compressed air and a flushing medium. The flushing medium flow channel is arranged to lead the flushing medium to the bottom of the borehole. The arrangement also includes a percussion hammer , which includes a compressed air operated percussion piston adapted in a cylinder of the percussion hammer, as well as hole drilling means for drilling a hole for the casing. The flushing medium flow channel is adapted to bypass the percussion piston or which flushing medium flow channel is adapted to pass through the percussion piston, and in which arrangement the drilling means additionally includes splines transmitting a rotating motion and adapted to conduct the compressed air that used the percussion piston through the splines.

A system and method are used in drilling a borehole in a formation. A trip to move a drillstring in the borehole is identified, where the trip is expected to produce a piston effect that changes a downhole pressure of the fluid in the borehole. A peak speed to move the drillstring in the borehole is calculated for the trip, and adjustments to a surface backpressure of the drilling system is calculated for the trip at the calculated peak speed to keep the downhole pressure within a tolerance of the formation. The drillstring is moved in the trip according to the calculated peak speed, and the downhole pressure change produced by the piston effect is counteracted by automatically adjusting the surface backpressure according to the calculated adjustments.

A casing running tool is provided. The casing running tool includes one or more sensors built into the casing running tool; an electronics housing that includes one or more power sources for powering the one or more sensors; one or more circuit boards for converting sensor data for transmission and transmission means for transmitting sensor data. The one or more sensors sense tool status and operational parameters of the casing running tool including axial load, axial position, torque, turns, internal mud pressure, hook load, tension, rotation speed, rotational position, vibration, alignment, X, Y, Z acceleration and temperature. A system is also provided for detection, processing and transmission of one or parameters of tool status and operational status of a casing running tool or associated tools in a casing installation or casing while drilling operation. The system includes a casing running tool; and a processor for receiving sensor data for processing and transmitting processed data in real-time for viewing by an operator. A method is further provided for performing a casing installation or casing while drilling operation.

A drill string apparatus includes an upper casing section having a port collar. The port collar provides a controllable opening from an interior of the upper casing section to an annulus around the upper casing section. A lower casing section is coupled to the upper casing section through a swivel. The lower casing section includes an external casing packer and a casing pad coupled to an external portion of the lower casing section. The external casing packer is expandable to an annulus around the lower casing section before a cement operation to avoid cement loss circulation to weak formation below the packer.