Iris valve type well annular pressure control device and method

1. A well annular pressure control device, comprising:

a housing having a through bore and at least two iris valves within the housing;

each iris valve comprising a plurality of vanes operable between an open position and a closed position to define an opening;

wherein at least one vane of the plurality of vanes comprises at least one flow orifice;

at least one actuator coupled to the plurality of vanes to move the plurality of vanes between the open position and the closed position,

wherein each of the iris valves is separately operable to define a corresponding size opening.

2. The device of claim 1 wherein the at least one actuator comprises a motor rotationally coupled to a cam plate, the cam plate having slots therein engageable with a cam pin on each of the plurality of vanes, wherein the slots are shaped to move the cam pins radially with respect to the through bore when the cam plate is rotated.

3. The device of claim 2 further comprising at least one stationary plate disposed in the housing and arranged to movably support a set of the plurality of vanes.

4. The device of claim 2 wherein the cam plate is rotatably supported in the housing by a bearing.

5. The device of claim 2 wherein the motor comprises at least one of an electric motor, a hydraulic motor, and a pneumatic motor.

6. The device of claim 2 wherein the rotatable coupling between the motor and the cam plate comprises a pinion gear on an output shaft of the motor and a ring gear disposed on an outer circumference of the cam plate.

7. The device of claim 1 further comprising a first seal disposed between the housing and the cam plate, a second seal disposed between the cam plate and each of the plurality of vanes and a third seal disposed between the plurality of vanes and the stationary plate.

8. The device of claim 1 wherein the plurality of vanes each comprise a leading edge, the leading edge comprising at least one of a seal element, a wear resistant coating and a wear resistant element.

9. The device of claim 1 wherein each of the plurality of vanes comprises a curved leading edge.

10. The device of claim 9 wherein a curvature of the curved leading edge is selected to optimize sealing against a selected outer diameter pipe.

11. The device of claim 1 wherein each of the plurality of vanes comprises a seal on at least one of a leading edge and a trailing edge, the seal arranged to sealingly engage an adjacent one of the plurality of vanes.

12. The device of claim 1 wherein multiple vanes of the plurality of vanes each comprise at least one flow orifice, wherein at least one of the iris valves enables fluid flow when the plurality of vanes are in the closed position.

13. The device of claim 1 wherein a diameter of the opening defined when a plurality of vanes are in the open position is at least as large as an internal diameter of the through bore.

14. A method for operating an annular control device in a wellbore, the annular control device comprising a housing having a through bore and at least two axially separated iris valves within the housing, each iris valve comprising a plurality of vanes operable between an open position and a closed position to define an opening and at least one actuator coupled to the plurality of vanes to move the plurality of vanes between the open position and the closed position, the method comprising:

operating a first one of the at least two iris valves to close toward a pipe;

operating a second one of the at least two iris valves to close toward an enlarged external diameter feature on the pipe;

moving the pipe longitudinally until the enlarged external diameter feature is disposed proximate the first one of the at least two iris valves;

opening the first one of the at least two iris valves to enable movement of the enlarged external diameter feature into the first one of the at least two iris valves;

moving the pipe until the enlarged external diameter feature clears the second one of the at least two iris valves; and

operating the second one of the at least two iris valves to close toward the pipe.

15. The method of claim 14 further comprising changing an amount of opening of at least one of the first iris valve and the second iris valve to maintain a selected pressure in an annular space in the wellbore.

16. A method for operating an annular control device in a wellbore, the annular control device comprising a housing having a through bore and at least two axially separated iris valves within the housing, each iris valve comprising a plurality of vanes operable between an open position and a closed position to define an opening and at least one actuator coupled to the plurality of vanes to move the plurality of vanes between the open position and the closed position, the method comprising:

a. opening a first one of the at least two iris valves;

b. operating a second one of the at least two iris valves to define an opening smaller than that defined by the fully open position;

c. moving fluid through the first and second iris valves;

d. opening the second iris valve to the fully open position; and

e. closing the first iris valve to define an opening smaller than that defined by the fully open position.

17. The method of claim 16 further comprising repeating a) through e) at selected times to reduce build-up of solids in the annular control device.

18. The method of claim 16 further comprising measuring pressure of the fluid and determining presence of solids in the annular control device from the measurements of pressure.

19. The method of claim 16 further comprising changing an amount of opening of one or both of the axially separated iris valves to maintain a selected pressure in an annular space in the wellbore.