Rolling cutter with improved rolling efficiency

1. A cutting structure, comprising:

an outer support element located on a blade of a downhole tool; and

an inner rotatable cutting element comprising a cutting surface at its upper end, the cutting surface comprising an ultrahard material, the cutting surface being rotatable about the inner rotatable cutting element axis;

wherein the inner rotatable cutting element comprises at least one line contact along a circumferential side surface thereof or a combination of at least one line contact along a circumferential side surface thereof and at least one point contact at a bottom face thereof, wherein the at least one line contact is between the inner rotatable cutting element and at least one pin that extends axially, and wherein the at least one pin is disposed in a groove in the outer support element.

2. The cutting structure of claim 1 , further comprising a plurality of line contacts between the inner rotatable cutting element and a plurality of pins.

3. The cutting structure of claim 2 , wherein the plurality of pins extend circumferentially around the inner rotatable cutting element by about 30 to 180 degrees.

4. The cutting structure of claim 3 , wherein the plurality of pins extend circumferentially around the inner rotatable cutting element by about 45 to 120 degrees.

5. The cutting structure of claim 1 , wherein the at least one pin has an exposure height of up to 4 mm greater than the outer support element.

6. The cutting structure of claim 1 , wherein the at least one pin is formed of a carbide, boride, nitride, polycrystalline diamond, or thermally stable polycrystalline diamond.

7. The cutting structure of claim 1 , wherein the at least one point contact is between the inner rotatable cutting element and at least one ball.

8. The cutting structure of claim 7 , wherein the at least one ball is disposed in a groove formed in the outer support element.

9. The cutting structure of claim 7 , wherein the at least one ball has an exposure height of at least 1 mm greater than the outer support element.

10. The cutting structure of claim 7 , wherein the at least one ball is formed of a carbide, boride, nitride, polycrystalline diamond, or thermally stable polycrystalline diamond.

11. The cutting structure of claim 7 , wherein the at least one ball is fixedly attached to the outer support element.

12. The cutting structure of claim 1 , further comprising a plurality of point contacts between the inner rotatable cutting element and a plurality of balls.

13. The cutting structure of claim 1 , wherein the at least one pin is a roller pin.

14. The cutting structure of claim 1 , wherein the at least one pin is a block pin.

15. The cutting structure of claim 1 , wherein the at least one pin is fixedly attached to the outer support element.

16. The cutting structure of claim 1 , wherein the outer support element is a sleeve extending a partial length of the inner rotatable cutting element.

17. The cutting structure of claim 16 , wherein a retaining ring is disposed within a circumferential groove formed around the circumferential side surface of the inner rotatable cutting element and a cut-out formed in an inner surface of the sleeve to axially retain the inner rotatable cutting element within the sleeve.

18. The cutting structure of claim 16 , wherein the inner rotatable cutting element comprises a shaft disposed within the sleeve, wherein the diameter of the upper end of the inner rotatable cutting element is substantially equal to an outer diameter of the sleeve, and wherein the diameter of the shaft is substantially equal to an inner diameter of the sleeve.

19. The cutting structure of claim 1 , wherein the cutting face is planar.

20. A downhole cutting tool, comprising:

a cutting element support structure on a blade having at least one cutter pocket formed therein;

at least one rotatable cutting element disposed within the at least one cutter pocket,

where in the at least one rotatable cutting element comprises a cutting surface at its upper end, the cutting surface comprising an ultrahard material, the cutting surface being rotatable about the at least one rotatable cutting element axis;

at least one pin disposed in a groove in the cutting element support structure adjacent a circumferential side surface of the at least one rotatable cutting element, the at least one pin extending parallel to the axis of the at least one rotatable cutting element; and

at least one retaining element configured to retain the rotatable cutting element in the cutter pocket.

21. The downhole cutting tool of claim 20 , further comprising a sleeve at least partially surrounding the at least one rotatable cutting element, wherein the at least one pin is disposed between the sleeve and the at least one rotatable cutting element.

22. The downhole cutting tool of claim 20 , wherein the at least one pin is disposed between the cutter pocket and the at least one rotatable cutting element.

23. A downhole cutting tool, comprising:

a cutting element support structure having at least one cutter pocket formed therein;

at least one rotatable cutting element disposed within the at least one cutter pocket,

where in the at least one rotatable cutting element comprises a cutting surface at its upper end;

at least one ball disposed adjacent a planar bottom face of the at least one rotatable cutting element;

at least one retaining element configured to retain the rotatable cutting element in the cutter pocket; and

a sleeve at least partially surrounding the at least one rotatable cutting element, wherein the at least one ball is disposed between the sleeve and the at least one rotatable cutting element.

24. The downhole cutting tool of claim 23 , wherein the at least one ball is disposed between the cutter pocket and the at least one rotatable cutting element.