A downhole system includes a drill string having a drilling fluid flow channel and at least one turbine alternator deployed in the flow channel. The turbine alternator is configured to convert flowing drilling fluid to electrical power. A voltage bus is configured to receive electrical power from the turbine alternator and at least one electrical motor is configured to receive electrical power from the voltage bus. An electronic controller is configured to provide active control of the turbine alternator via processing a desired speed of the electrical motor to generate a desired torque current and feeding the desired torque current forward to the turbine alternator. The turbine alternator is responsive to the desired torque current such that it modifies the electrical power provided to the voltage bus in response to the desired torque.

A downhole system includes a drill string having a drilling fluid flow channel and at least one turbine alternator deployed in the flow channel. The turbine alternator is configured to convert flowing drilling fluid to electrical power. A voltage bus is configured to receive electrical power from the turbine alternator and at least one electrical motor is configured to receive electrical power from the voltage bus. An electronic controller is configured to provide active control of the turbine alternator via processing a desired speed of the electrical motor to generate a desired torque current and feeding the desired torque current forward to the turbine alternator. The turbine alternator is responsive to the desired torque current such that it modifies the electrical power provided to the voltage bus in response to the desired torque.

A downhole disconnect tool can include outer housing sections connected to each other with threads, and an inner sleeve received in at least one of the outer housing sections, whereby the inner sleeve limits relative rotation between the outer housing sections in a connect position, and permits relative rotation between the outer housing sections in a disconnect position. A method of disconnecting portions of a tubular string can include connecting a downhole disconnect tool between the tubular string portions, deploying a plug into the tubular string, thereby engaging the plug with an inner sleeve in the downhole disconnect tool, applying a differential pressure across the plug, thereby displacing the inner sleeve relative to outer housing sections of the downhole disconnect tool, and then unthreading the outer housing sections from each other in the well.

A method comprises rotating a drill bit of a drilling system at at least 1000 rpm. The drill system can comprise a drill feed, a drill head comprising a motor and coupled to the drill feed, a drill string, comprising at least one drill rod, operatively coupled to the drill head so that the drill head is configured to axially and rotationally drive the drill string, and the drill bit coupled to the bottom end of the drill string.

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 fluid operated drilling device for drilling a hole said device having a hammer, a rotation device and a drill rod. The hammer includes a tubular main body, a back head, a cylindrical piston housing, a reciprocating piston, a space, a valve unit and a fluid pressure supply unit. A hollow portion of the piston is open to lead pressurized operating fluid directly to the hollow portion from the fluid pressure supply passage. The hammer includes an axial exhaust passage formed between the main body and the piston housing. The valve unit includes a valve exhaust passage and the piston has a lower part and an upper part detachably connected to each other. The invention also relates to a method for drilling a hole using the fluid operated drilling device.

A fluid operated drilling device for drilling a hole said device having a hammer, a rotation device and a drill rod. The hammer includes a tubular main body, a back head, a cylindrical piston housing, a reciprocating piston, a space, a valve unit and a fluid pressure supply unit. A hollow portion of the piston is open to lead pressurized operating fluid directly to the hollow portion from the fluid pressure supply passage. The hammer includes an axial exhaust passage formed between the main body and the piston housing. The valve unit includes a valve exhaust passage and the piston has a lower part and an upper part detachably connected to each other. The invention also relates to a method for drilling a hole using the fluid operated drilling device.

Methods for operating drill strings in a wellbore include providing a drilling apparatus that includes a Kelly drive system for rotating the drill string that includes a bottom hole assembly (BHA) and a Kelly engaged with the Kelly drive system. The BHA includes a hydraulically driven rotating string reamer coupled to the drill string uphole from a drill bit and a near-bit reamer. The hydraulically driven rotating string reamer includes a hydraulic drive operatively coupled to a string reamer. The methods include translating the BHA axially through the wellbore and, while translating the BHA, circulating drilling fluid through the drill string, which causes the hydraulic drive to rotate the string reamer relative to the drill string, drill bit, and near-bit reamer. Rotation of the string reamer by the hydraulic drive reams away imperfections extending radially inward from a wellbore wall of the wellbore.

A method for maintaining a penetration rate of a drilling operation, where the drilling operation is carried out by a drilling rig having a hammer drill apparatus. A reference penetration rate for the hammer drill bit is chosen. A starting depth of cut is computed from the reference penetration rate, the measured hammer frequency, and the drill bit parameters. The system measures the actual penetration rate of the drill bit and computes an actual depth of cut. From the actual depth of cut a target bit rotation speed is computed. The target rotation speed is compared to the actual rotation speed, and the rotation speed is adjusted up or down to set the bit rotation speed at a value that will maintain the target rotation speed, notwithstanding changes in hammer frequency or ground conditions.

A downhole system includes a drill string having a drilling fluid flow channel and at least one turbine alternator deployed in the flow channel. The turbine alternator is configured to convert flowing drilling fluid to electrical power. A voltage bus is configured to receive electrical power from the turbine alternator and at least one electrical motor is configured to receive electrical power from the voltage bus. An electronic controller is configured to provide active control of the turbine alternator via processing a desired speed of the electrical motor to generate a desired torque current and feeding the desired torque current forward to the turbine alternator. The turbine alternator is responsive to the desired torque current such that it modifies the electrical power provided to the voltage bus in response to the desired torque.