Centralizer for downhole probes

1. A downhole assembly comprising:

a drill string section having a bore extending longitudinally through the drill string section, the bore having a bore diameter;

a downhole probe located in the bore of the section; and

a centralizer in the bore, the centralizer comprising a plurality of tubular members arranged end to end, each of the tubular members having a wall extending around the downhole probe, the wall of each of the tubular members formed to, along a length of each of the tubular members, alternatingly contact an inside wall surface of the bore at a first plurality of locations spaced apart around a circumference of the bore and an outside surface of the downhole probe at a second plurality of locations spaced apart around a circumference of the probe, a cross-section of each of the tubular member walls following a path around the downhole probe that zig zags back and forth between the outside surface of the downhole probe and the inside wall surface of the bore;

wherein each of the tubular members in an uninstalled configuration has outermost points lying on a circle, the circle having a diameter that is larger than the bore diameter.

2. The downhole assembly of claim 1 wherein an end of a first tubular member of the centralizer abuts an opposing end of a second tubular member that is adjacent to the first tubular member.

3. The downhole assembly of claim 1 wherein the plurality of tubular members support the probe substantially continuously along an otherwise unsupported portion of the probe.

4. The downhole assembly of claim 3 wherein the plurality of tubular members support the probe substantially continuously along at least 60% of the otherwise unsupported portion of the probe.

5. The downhole assembly of claim 3 wherein the plurality of tubular members support the probe substantially continuously along at least 95% of the otherwise unsupported portion of the probe.

6. The downhole assembly of claim 1 wherein the plurality of tubular members support the probe for at least 6 meters of an otherwise unsupported portion of the probe.

7. The downhole assembly of claim 1 wherein lengths of the plurality of tubular members are equal to one another.

8. The downhole assembly according to claim 1 wherein the tubular members are resiliently deformable to accommodate the probe.

9. The downhole assembly according to claim 1 wherein the tubular members are resiliently deformable to fit inside the bore.

10. The downhole assembly according to claim 1 wherein the tubular members exert a compressive force on the probe to hold the probe concentric within the bore.

11. The downhole assembly according to claim 1 wherein the tubular members and the probe form an interference fit.

12. The downhole assembly according to claim 1 wherein the probe is slidable longitudinally into the tubular members of the centralizer.

13. The downhole assembly according to claim 1 comprising a layer of a vibration damping material between a housing of the downhole probe and the tubular members of the centralizer.

14. The downhole assembly according to claim 1 wherein the cross-section of each of the tubular member walls provides:

first outwardly-convex and inwardly-concave lobes, the first lobes contacting the inside wall surface of the bore of the drill string section at the first plurality of locations spaced apart around the circumference of the bore; and

a plurality of inwardly-projecting portions, each of the plurality of inwardly-projecting portions arranged between two adjacent ones of the plurality of first lobes.

15. The downhole assembly according to claim 14 wherein the inwardly-projecting portions are shaped to conform to the outside surface of the probe.

16. The downhole assembly according to claim 14 wherein the first lobes are shaped to conform to the inside wall surface of the bore.

17. The downhole assembly according to claim 14 wherein the inwardly-projecting lobes are mirror symmetrical about an axis passing through a longitudinal centerline of the tubular members.

18. The downhole assembly according to claim 14 wherein a thickness of the wall of each of the tubular members of the centralizer is substantially uniform.

19. The downhole assembly according to claim 14 wherein in cross-section each of the tubular members has 4-fold rotational symmetry.

20. The downhole assembly according to claim 14 wherein the cross-section provides four first lobes.

21. The downhole assembly according to claim 14 wherein the cross-section provides two to eight first lobes.

22. The downhole assembly according to claim 1 wherein the wall of each of the tubular members comprises PEEK or PET.

23. A downhole assembly comprising:

a drill string section having a bore extending longitudinally through the drill string section, the bore having a diameter;

a downhole probe located in the bore of the section; and

a centralizer in the bore, the centralizer comprising a plurality of centralizer members arranged end to end, each of the centralizer members formed to alternatingly contact an inner wall of the bore along a length of the centralizer member at a plurality of locations spaced apart around a circumference of the bore and the probe along the length of the centralizer member at a plurality of locations spaced apart around a circumference of the probe;

wherein each of the centralizer members in an uninstalled configuration has outermost points lying on a circle, the circle having a diameter that is larger than the bore diameter.

24. The downhole assembly of claim 23 wherein each of the centralizer members comprises a tubular member having a wall extending around the downhole probe, the wall formed to contact the inner wall of the bore and an outside surface of the downhole probe.