Rotating control device with variable pressure compensation

1 . A rotating control device (RCD) defining a longitudinal passage through which a tubular extends in an axial direction, the RCD comprising:

a drive guide element surrounding the tubular and co-rotating with the tubular;

a bearing housing comprising at least one bearing assembly for rotatably supporting the drive guide element;

a rotary seal housing comprising a plurality of rotary seals surrounding the drive guide element and configured to limit ingress of a working fluid flowing around the tubular into the bearing housing, the plurality of rotary seals arranged in the axial direction, the plurality of rotary seals comprising a first rotary seal and a second rotary seal positioned axially downstream from the first rotary seal;

a plurality of fluid lines in communication with a plurality of radial passages containing a pressure compensating fluid for controlling a pressure differential across the plurality of rotary seals, the plurality of fluid lines comprising a first fluid line and a second fluid line, the plurality of radial passages comprising a first radial passage in communication with the first fluid line and a second radial passage in communication with the second fluid line;

a pressure compensating piston positioned axially upstream from the first rotary seal, the pressure compensating piston configured to build pressure of the pressure compensating fluid in the first radial passage in response to flow of the working fluid to control the pressure differential across the first rotary seal; and

a variable pressure compensating device positioned in the second fluid line axially downstream from the second rotary seal, wherein the variable pressure compensating device is configured to build pressure of the pressure compensating fluid in the second radial passage in response to a leak across the second rotary seal to control the pressure differential across the second rotary seal.

2 . The RCD of claim 1 , wherein the variable pressure compensating device comprises a moveable member positioned in a chamber and moveable therein in response to excessive pressure compensating fluid in the second radial passage from the leak across the second rotary seal.

3 . The RCD of claim 2 , wherein the moveable member is a piston operably connected with a biasing means that is configured to control movement of the piston in the chamber.

4 . The RCD of claim 1 , wherein the pressure compensating piston is positioned in a pressure compensating chamber and moveable therein in response to the flow of the working fluid.

5 . The RCD of claim 1 , wherein the first fluid line is isolated from the second fluid line.

6 . The RCD of claim 1 , wherein the plurality of fluid lines extend through the bearing housing and the rotary seal housing toward the plurality of radial passages, and wherein the plurality of fluid lines are defined at discrete circumferential positions.

7 . The RCD of claim 6 , further comprising at least one bearing fluid line communicating with an internal volume of the bearing housing, wherein the at least one bearing fluid line extends through the bearing housing at a discrete circumferential position.

8 . The RCD of claim 1 , wherein the plurality of radial passages are isolated from one another via the plurality of rotary seals.

9 . The RCD of claim 1 , wherein the plurality of rotary seals are supported by a plurality of seal retainers, wherein the plurality of seal retainers define at least some of the plurality of radial passages.

10 . The RCD of claim 1 , wherein the variable pressure compensating device is configured to operate independently of the pressure compensating piston, and wherein the pressure compensating fluid in the second radial passage is configured to remain unpressurized until the leak across the second rotary seal occurs.

11 . The RCD of claim 1 , wherein:

the plurality of rotary seals further comprises a third rotary seal positioned axially downstream from the second rotary seal;

the plurality of fluid lines further comprises a third fluid line;

the plurality of radial passages further comprises a third radial passage in communication with the third fluid line;

the variable pressure compensating device is a first variable pressure compensating device;

the RCD further comprises a second variable pressure compensating device positioned in the third fluid line axially downstream from the third rotary seal, wherein the second variable pressure compensating device is configured to build pressure of the pressure compensating fluid in the third radial passage in response to a leak across the third rotary seal;

the second fluid line and the third fluid line are each isolated from the first fluid line and the pressure compensating piston;

the first variable pressure compensating device and the second variable pressure compensating device are each configured to operate independently of the pressure compensating piston;

the pressure compensating fluid in the second radial passage is configured to remain unpressurized until the leak across the second rotary seal occurs; and

the pressure compensating fluid in the third radial passage is configured to remain unpressurized until the leak across the third rotary seal occurs.

12 . A system comprising:

a rotating control device (RCD) defining a longitudinal passage; and

a tubular extending through the longitudinal passage of the RCD in an axial direction;

wherein the RCD comprises:

a drive guide element surrounding the tubular and co-rotating with the tubular;

a bearing housing comprising at least one bearing assembly for rotatably supporting the drive guide element;

a rotary seal housing comprising a plurality of rotary seals surrounding the drive guide element and configured to limit ingress of a working fluid flowing around the tubular into the bearing housing, the plurality of rotary seals arranged in the axial direction, the plurality of rotary seals comprising a first rotary seal and a second rotary seal positioned axially downstream from the first rotary seal;

a plurality of fluid lines in communication with a plurality of radial passages containing a pressure compensating fluid for controlling a pressure differential across the plurality of rotary seals, the plurality of fluid lines comprising a first fluid line and a second fluid line, the plurality of radial passages comprising a first radial passage in communication with the first fluid line and a second radial passage in communication with the second fluid line;

a pressure compensating piston positioned axially upstream from the first rotary seal, the pressure compensating piston configured to build pressure of the pressure compensating fluid in the first radial passage in response to flow of the working fluid to control the pressure differential across the first rotary seal; and

a variable pressure compensating device positioned in the second fluid line axially downstream from the second rotary seal, wherein the variable pressure compensating device is configured to build pressure of the pressure compensating fluid in the second radial passage in response to a leak across the second rotary seal to control the pressure differential across the second rotary seal.

13 . The system of claim 12 , further comprising a fluid system configured to supply the working fluid through the tubular toward a bottom of a wellbore.

14 . The system of claim 13 , wherein an annulus surrounding the tubular is configured to direct a returning working fluid from the wellbore toward a surface, and wherein the plurality of rotary seals is configured to limit ingress of the returning working fluid into the bearing housing.

15 . The system of claim 12 , wherein the variable pressure compensating device comprises a piston positioned in a chamber and moveable therein in response to excessive pressure compensating fluid in the second radial passage from the leak across the second rotary seal, wherein the piston is operably coupled with a biasing means that is configured to control movement of the piston in the chamber.

16 . The system of claim 12 , wherein the pressure compensating piston is positioned in a pressure compensating chamber and moveable therein in response to the flow of the working fluid.

17 . A method of operating a drilling system, the method comprising:

supplying a working fluid through a tubular into a wellbore for performing one or more downhole operations using the tubular;

controlling flow of the working fluid returning from the wellbore through an annulus surrounding the tubular using the RCD of claim 1 ; and

isolating the bearing housing from the flow of the working fluid returning from the wellbore using the plurality of rotary seals, wherein, in response to the leak across the second rotary seal, the variable pressure compensating device operates to build pressure of the pressure compensating fluid in the second radial passage to control the leak.

18 . The method of claim 17 , further comprising building pressure of the pressure compensating fluid in the first radial passage upstream from the second radial passage using the pressure compensating piston.

19 . The method of claim 18 , wherein the variable pressure compensating device builds pressure in the second radial passage independently of the pressure compensating piston building pressure in the first radial passage.

20 . The method of claim 17 , wherein, before the leak across the second rotary seal occurs, the pressure compensating fluid in the second radial passage is unpressurized.