A dual gradient drilling system includes a subsea blowout preventer disposed above a wellhead, the subsea blowout preventer having a central lumen configured to provide access to a wellbore, a lower section of a marine riser fluidly connected to the subsea blowout preventer, a closed-hydraulic positive displacement subsea pump system fluidly connected to the lower section of the marine riser and disposed at a predetermined depth, an annular sealing system disposed above the closed-hydraulic positive displacement subsea pump system, and an independent mud return line fluidly connecting one or more pump heads of the closed-hydraulic positive displacement subsea pump system to a choke manifold disposed on a floating platform of a rig.

The equivalent circulating density (ECD) in a wellbore may be managed during a wellbore operation using ECD models that take into account the rheology of the wellbore fluid and the rotational speed of tubulars in the wellbore. For example, a method may include rotating a rotating tubular in a stationary conduit while flowing a fluid through an annulus between the rotating tubular and the stationary conduit; calculating an equivalent circulating density (ECD) of the fluid where a calculated viscosity of the fluid is based on an ECD model ?_eff=f(? ?_eff)*h(Re), wherein ?_eff is the viscosity of the fluid, ? ?_eff is an effective shear rate of the fluid, and Re is a Reynold's number for the fluid for the rotational speed of the rotating tubular; and changing an operational parameter of the wellbore operation to maintain or change the ECD of the fluid.

An assembly is used with a remote source of hydraulic power to control flow of wellbore fluid in a drilling system. At least one choke is operable to control the flow of the fluid to other portions of the system. At least one hydraulic actuator disposed with the choke actuates operation of the choke in response to the hydraulic power. At least one control valve disposed with the choke controls supply of the hydraulic power to and controls return of the hydraulic power from the actuator. An accumulator can be disposed with the choke and coupled to the supply upstream of the control valve. The control valve can couple to the actuator with a pair of pilot-operated check valves disposed in fluid communication between the control valve and the actuator. A stage tank and stage pump can be disposed with the choke. The tank receives the return from the control valve, and the stage pump can pump the return from the stage tank to the source.

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.

The systems, devices, and methods described herein describe a control system that automatically determines a trip speed for a surge operation or a swab operation. The control system is used to automatically adjust the trip speed during the respective surge or swab operation in order to optimize the trip speed according to the changing environment of the wellbore that the bottom hole assembly traverses without exceeding the fracture gradient in the wellbore location. A well plan identifies formations along the wellbore route, dynamic real-time tracking of the tubulars added to the drill string and removed therefrom identifies the current location of the BHA in the wellbore, and pressure and fractional gradient at the location of the BHA, and in some embodiments a real-time pressure measurement from the BHA, together are used to automatically determine the maximum tripping speed possible for the formation that the BHA is traversing.

A multi-fluid drilling system (10) drilling is disclosed for drilling a hole or well (11). The system (10) is coupled to a dual wall drill string (12). The drill string (12) is configured to enable separate flow of a first fluid (14) and a second fluid (16). The system (10) has a hammer (22) and a downhole motor (24). Both the hammer (22) and the motor (24) are supported by and are coupled to the drill string (12). The motor (24) is uphole of the hammer (22). The hammer (22) is arranged so that when supported by the drill string (12) the first fluid (14) when flowing through the drill string (12) is able to flow to and power the hammer (22). As the motor (24) is disposed between the hammer (22) and the drill string (2) the first fluid (14) is also able to flow through the motor (24). To this end the motor (24) has a channel (25) to enable the first fluid to flow from the drill sting (12) to the hammer (22). The channel (25) acts as a part of a flow path or conduit for the first fluid (14).

A system includes a mud return system. The mud return system includes a pressure exchanger (PX) configured to be installed in a body of water, to receive used drilling mud, to receive a second fluid, to utilize the second fluid to pressurize the drilling mud for transport, via a mud return line, from a first location at or near the sea floor to a second location at or near a surface of the body of water.

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.

A fluid transfer device for use in wellbore drilling includes at least one pressure vessel having a fluid port at a bottom thereof for entry and discharge of one of a working fluid or a power fluid and a fluid port at a top thereof for entry and discharge of the other of the power fluid or the working fluid. The pressure vessel has a barrier fluid between the power fluid and the working fluid. Valves are coupled to the power fluid port for selective introduction of the power fluid into the at least one pressure vessel. Valves are coupled to the working fluid port such that the working fluid is constrained to flow in only one direction.

The systems, devices, and methods described herein describe a control system that automatically determines a trip speed for a surge operation or a swab operation. The control system is used to automatically adjust the trip speed during the respective surge or swab operation in order to optimize the trip speed according to the changing environment of the wellbore that the bottom hole assembly traverses without exceeding the fracture gradient in the wellbore location. A well plan identifies formations along the wellbore route, dynamic real-time tracking of the tubulars added to the drill string and removed therefrom identifies the current location of the BHA in the wellbore, and pressure and fractional gradient at the location of the BHA, and in some embodiments a real-time pressure measurement from the BHA, together are used to automatically determine the maximum tripping speed possible for the formation that the BHA is traversing.