A double-layer coiled tubing double-gradient drilling system, on the basis of conventional drilling equipment, includes a double-layer coiled tubing system, separating fluid, a downhole lifting pump system, throttling control systems and a data monitoring system. Power fluid enters an annular space of the tubing through an adapter, passes through a downhole lifting pump, enters an inner pipe through a bridge channel, and enters the bottom hole through the drill bit. Return fluid enters an annular channel of the tubing through a recovery hole, then enters the inner pipe through the bridge channel and enters the lifting pump, and then enters a solid control system through the adapter and the control systems in sequence. Gradient control of the bottom hole pressure is realized through monitoring of the separating fluid and control of the drilling pump unit and throttling control systems. The problem of narrow safe drilling density window is solved.

A coupling assembly includes a coupling, a protective ring and two tubulars, the coupling of generally cylindrical shape with a channel therethrough, the coupling having at least one internal thread and two coupling ends and a pin end of at least one of the two tubulars having an external thread for threaded mating therewith so that the coupling assembly provides a connection between the two tubulars, the protective ring including a ring body for positioning adjacent an interior wall of the coupling between the two ends thereof, the ring body being generally cylindrical and having a ring channel therethrough, the protective ring includes one of a tongue and groove and at least one of the ends of at least one of the two tubulars having the other of a tongue and groove.

A coupling assembly includes a coupling, a protective ring and two tubulars, the coupling of generally cylindrical shape with a channel therethrough, the coupling having at least one internal thread and two coupling ends and a pin end of at least one of the two tubulars having an external thread for threaded mating therewith so that the coupling assembly provides a connection between the two tubulars, the protective ring including a ring body for positioning adjacent an interior wall of the coupling between the two ends thereof, the ring body being generally cylindrical and having a ring channel therethrough, the protective ring includes one of a tongue and groove and at least one of the ends of at least one of the two tubulars having the other of a tongue and groove.

A threaded coupling comprising a first end, a second end, a first portion of the threaded coupling defining a first thread profile, a second portion of the threaded coupling defining a second thread profile different from the first thread profile, where at least two threads of the second thread profile proximate to the second end are reduced in height according to an extra machining angle.

A threaded coupling comprising a first end, a second end, a first portion of the threaded coupling defining a first thread profile, a second portion of the threaded coupling defining a second thread profile different from the first thread profile, where at least two threads of the second thread profile proximate to the second end are reduced in height according to an extra machining angle.

A sealing system connecting first and second tubular members includes a first curvilinear sealing surface on the first tubular member and a second curvilinear sealing surface on the second tubular member. Both the first and second curvilinear sealing surfaces are disposed between two sets of threading on the respective first and second tubular members. When the first and second tubular members are in a connected configuration, the first and second curvilinear sealing surfaces contact and interfere to form an annular curvilinear center seal. A relief pocket may be disposed adjacent to the first and/or second curvilinear sealing surfaces to contain excess lubricant between the first and second tubular members.

A sealing system connecting first and second tubular members includes a first curvilinear sealing surface on the first tubular member and a second curvilinear sealing surface on the second tubular member. Both the first and second curvilinear sealing surfaces are disposed between two sets of threading on the respective first and second tubular members. When the first and second tubular members are in a connected configuration, the first and second curvilinear sealing surfaces contact and interfere to form an annular curvilinear center seal. A relief pocket may be disposed adjacent to the first and/or second curvilinear sealing surfaces to contain excess lubricant between the first and second tubular members.

A system includes a top drive system; a drilling riser running tool configured to be deployed by the top drive system; a fluid line configured to run from the top drive system to the drilling riser running tool; and a liquid filing system. The drilling riser running tool includes a tool head module configured to engage and hold a first riser joint at a top end such that with the top drive system above the drilling riser running tool, the first riser joint can be lowered towards a second riser joint being held near a drill floor. The first riser joint includes a central tube and a first auxiliary line. The liquid filling system is configured to provide liquid filling of the first auxiliary line via the fluid line after connection of the first and second riser joints and while the first and second riser joints are being run.

A tubular includes a carbon steel main body defining a first flow passage. The carbon steel main body includes a first end and a second end. The carbon steel main body includes a beveled edge at the first end of the carbon steel main body. A corrosion resistant pup defines a second flow passage in-line with the first flow passage. The corrosion resistant pup includes a substantially same inner diameter and outer diameter as the carbon steel main body. The corrosion resistant pup includes a first end and a second end. The corrosion resistant pup includes a first beveled edge at the first end. The corrosion resistant pup is connected to the carbon steel main body by a weld along the beveled edge of the carbon steel main body and the beveled edge of the corrosion resistant pup.

Detector device (10) mounts to a drilling rig (12) to sense sound or vibration signalled from downhole. The device (10) has a transmitter (10,20) to transmit data and/or an alert relating to sensed sound and/or vibration associated with deployment and/or positioning of a tool downhole. The device (10) recognises that one or more predetermined events or a pattern of events or one or more particular sound and/or vibration signatures occur(s). Downhole device (36) has a transmitter (38) transmitting a signal indicating a sensed pressure, position or motion change downhole. Communication between the downhole device and the device at the surface to determine depth or distance e.g. time of flight of a signal emitted by one device and the return signal from the other device or from the send and received times of the signal between the two devices based on their respective timers.