Downhole impeller device

1. A downhole impeller device for use within a well having a well diameter and a surface, the device comprising:

a body connectable to a drill string and having an outer surface and an external diameter smaller than the well diameter so as to form an annulus between the body and the well such that drill fluid may flow within the drill string and within the annulus; and

at least two impeller members extending from the outer surface of the body such that rotation of the at least two impeller members impels drilling fluid within the annulus,

wherein the at least two impeller members defines at least one channel therebetween, the channel including an inwardly tapering throat portion such that the velocity of drilling fluid exiting the at least one channel is increased.

2. A downhole impeller device as claimed in claim 1 , wherein the ody has a longitudinal axis, and wherein at least one impeller member includes an impeller surface which is oriented at an oblique angle relative to the longitudinal axis of the body.

3. A downhole impeller device as claimed in claim 1 , wherein at least one impeller member includes an impeller surface which is oriented at an oblique angle relative to a plane which is normal to the longitudinal axis of the body.

4. A downhole impeller device as claimed in claim 1 , wherein each impeller member has an end portion, and wherein each impeller member extends from the outer surface of the body such that the end portion of each impeller member is substantially adjacent to the well.

5. A downhole impeller device as claimed in claim 1 , wherein the well includes a plurality of casing sections.

6. A downhole impeller device as claimed in claim 1 , wherein the well is an angled well.

7. A downhole impeller device as claimed in claim 1 , including a first stabilising member comprising a plurality of fins extending from the body towards the well.

8. A downhole impeller device as claimed in claim 7 , wherein the first stabilising member is provided above at least one impeller member.

9. A downhole impeller device as claimed in claim 7 , including a second stabilising member comprising a plurality of fins extending from the body towards the well.

10. A downhole impeller device as claimed in claim 9 , wherein the second stabilising member is provided below at least one impeller member.

11. A downhole impeller device as claimed in claim 9 , wherein at least one of the first and second stabilising members defines a first outer diameter and at least one impeller member defines a second outer diameter, and wherein the second outer diameter is smaller than the first outer diameter.

12. A downhole impeller device as claimed in claim 1 , wherein at least one impeller member is adapted to impel drilling fluid within the annulus towards the surface.

13. A downhole impeller device as claimed in claim 1 , wherein at least one impeller member is adapted to impel drilling fluid within the annulus in a radial direction outwardly from the body.

14. A downhole impeller device as claimed in claim 1 , wherein at least one channel is substantially helical.

15. A downhole impeller device as claimed in claim 1 , including pumping means.

16. A downhole impeller device as claimed in claim 15 , wherein at least one impeller member provides the pumping means.

17. A downhole impeller device as claimed in claim 1 , including agitating means such that the flow of drilling fluid within the annulus is made more turbulent.

18. A downhole impeller device as claimed in claim 17 , wherein at least one impeller member provides the agitating means.

19. A drill string including a downhole impeller device according to claim 1 .

20. A drill string as claimed in claim 19 , wherein a plurality of downhole impeller devices are provided.

21. A drill string as claimed in claim 20 , wherein each device is spaced apart at a distance of between 25 and 30 meters.

22. A method of removing debris within a well having a well diameter and an inner surface, the method comprising:

providing a drill string having an outer surface within the well such that the outer surface of the drill string and the inner surface of the well define an annulus;

pumping drilling fluid down the drill string such that the drilling fluid returns via the annulus; and

providing a downhole impeller device such that rotation of the downhole impeller device impels fluid within the annulus, wherein the downhole impeller device comprises a body connectable to the drill string and having the outer surface and an external diameter smaller than the well diameter so as to form the annulus between the body and the well such that drill fluid may flow within the drill string and within the annulus, and at least two impeller members extending from the outer surface of the body such that rotation of the at least two impeller members causes the rotation, the at least two impeller members defining at least one channel therebetween, the channel including an inwardly tapering throat portion such that the velocity of drilling fluid exiting the at least one channel is increased.

23. A method as claimed in claim 22 , including impelling drilling fluid within the annulus in a radial direction outwardly towards the inner surface of the well.

24. A method as claimed in claim 22 , including adapting at least one impeller member to provide pumping means such that the velocity of drilling fluid impelled by at least one impeller member is increased.

25. A method as claimed in claim 22 , including agitating the flow of drilling fluid within the annulus such that it is made more turbulent.

26. A method as claimed in claim 22 , including providing a plurality of impeller members at the outer surface of the drill string, and spacing at least one impeller member from another at least one impeller member by a distance of between 25 and 30 meters.

27. A method as claimed in claim 22 , including reciprocating the drill string.

28. A method as claimed in claim 22 , performed in an angled well.