A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

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.

Systems and processes for subsea marine managed pressure operations. One system includes a modified riser joint configured to fluidly connect inline with one or more riser joints. The modified riser joint and the one or more riser joints are connected to form a riser connecting a floating vessel with a wellhead. The system further includes a subsea pressure management sub-system configured to be operatively and fluidly connected to the modified riser joint at a subsea location.

A downhole tool for cleaning and sealing a wellbore includes a wash tool configured at a downhole end of the downhole tool to generate pulses of a first fluid at a first frequency and a first pressure for washing a target interval of a wellbore. The downhole tool further includes a plugging tool configured uphole or downhole from the wash tool to generate pulses of a second fluid at a second frequency and a second pressure for depositing a sealing plug at the target interval of the wellbore. The second fluid has a higher viscosity than the first fluid, the second frequency is lower than the first frequency, and the second pressure is higher than the first pressure.

A method for drilling a wellbore comprises using drilling mud having a mud weight less than the formation pore pressure while drilling the horizontal section, to release some formation gas to mix with the drilling mud. As the mixture flows up the wellbore annulus, the resulting pressure in the vertical section is within the mud weight window (MWW) of the weak zones, thereby maintaining wellbore stability without the need for intermediate casings. The wellbore is killed by introducing a volume of heavy mud via a circulation sub in the drill string and periodically introducing additional heavy mud to fill the void left behind by the drill string as it is pulled uphole. The ratio of light mud and heavy mud in the killed well is such that the resulting pressure in the vertical section is within the MWW of the weak zones.

Systems and processes for subsea marine managed pressure operations. One system includes a modified riser joint configured to fluidly connect inline with one or more riser joints. The modified riser joint and the one or more riser joints are connected to form a riser connecting a floating vessel with a wellhead. The system further includes a subsea pressure management sub-system configured to be operatively and fluidly connected to the modified riser joint at a subsea location.

Systems and processes for subsea marine managed pressure operations. One system includes a modified riser joint configured to fluidly connect inline with one or more riser joints. The modified riser joint and the one or more riser joints are connected to form a riser connecting a floating vessel with a wellhead. The system further includes a subsea pressure management sub-system configured to be operatively and fluidly connected to the modified riser joint at a subsea location.

The invention provides a mud circulation system for reducing swab pressure while tripping out, including drilling tool components, a normal drilling circulation channel and a tripping circulation channel, the drilling tool components include a drill string, a drill bit, and a top drive, the normal drilling circulation channel includes a first rotary valve, a solid phase control device, a mud tank, a mud pump, and a forth rotary valve connected in sequence, the tripping circulation channel includes a second rotary valve, a tripping mud pump, a tripping mud tank and a third rotary valve connected in sequence; the mud circulation system for reducing the swab pressure is operated to: shut down the mud pump, close the first rotary valve, and open the second rotary valve and the third rotary valve before tripping out; determine the pumping flow rate according to relevant parameters.

A method for managed pressure drilling comprising: extending a drilling riser with a drill string from a floating installation to a subsea blow-out preventer stack; providing a first fluid in the drilling riser annulus and a second fluid in a fluid conduit extending from the floating installation, where the first fluid has a higher density than the second fluid; circulating the second fluid through a control valve which is fluidly connected to the fluid conduit and operating the control valve to apply a surface back-pressure so as to obtain a pre-determined, desired combined hydrostatic and frictional circulation pressure below the subsea blow-out preventer stack.

Method for quantifying a volumetric flow rate of a flow of drilling mud in a floating structure for subsoil drilling, said method comprising: providing a flowmeter (50) on a floating structure (20) for subsoil drilling, said flowmeter (50) being configured for generating a flow signal (FS); providing a detection device (70) on said floating structure (20), suitable for generating a heave signal (HS) representative of a substantially vertical heave of said floating structure (20); acquiring said flow signal (FS) and said heave signal (HS) through a processor (60); activating said processor (60) in order to transform said flow signal (FS), thereby obtaining a corresponding first spectrum (S1) in the frequency domain; activating said processor (60) in order to transform said heave signal (HS), thereby obtaining a corresponding second spectrum (S2) in the frequency domain; activating said processor (60) in order to compare said first spectrum (S1) with said second spectrum (S2), thereby obtaining a resultant spectrum (RS); activating said processor (60) in order to transform said resultant spectrum (RS), thereby obtaining a corresponding resultant signal (SX) in the time domain; activating said processor (60) in order to: determine a mean value of said flow signal (FS), add said resultant signal (SX) to said mean value, thereby obtaining a quantification of a flow of drilling mud in said floating structure; activating said processor (60) in order to generate an output signal (OUT) representative of said quantification.