Orientation apparatus and hole finder device for a wireline logging tool string

1. A sensor transportation apparatus to convey an elongate sensor assembly through a wellbore, the sensor transportation apparatus comprising:

at least one engagement structure to connect the sensor transportation apparatus to the sensor assembly, and

a pair of skids, and

an orientation structure comprising at least three orientation projections, the orientation structure defining a form having a transverse outline which has a rotational centre, wherein the rotational centre is offset from a centre of mass of the elongate sensor assembly so that, in use, the sensor transportation apparatus is oriented in a most stable position with the centre of mass of the elongate sensor assembly below the rotational centre and with the pair of skids oriented to slide along a low side of the wellbore.

2. The sensor transportation apparatus as claimed in claim 1 wherein lateral extremities of the orientation structure on each side of a vertical centreline of the apparatus substantially lie on a substantially circular curve.

3. The sensor transportation apparatus as claimed in claim 1 , wherein the pair of skids are formed from a ceramic material or a plastic or elastomer material.

4. The sensor transportation apparatus as claimed in claim 1 , wherein the orientation structure comprises the pair of skids.

5. The sensor transportation apparatus as claimed in claim 4 , wherein each skid is a said orientation projection.

6. The sensor transportation apparatus as claimed in claim 1 , wherein the orientation projections act to destabilise the position of the elongate sensor assembly if placed in contact with the low side of the wellbore causing the elongate sensor assembly to rotate about a longitudinal axis of the elongate sensor assembly to an orientation placing the pair of skids in contact with the low side wall of the wellbore.

7. The sensor transportation apparatus as claimed in claim 1 , wherein lateral extremities of the orientation projections define sections of a perimeter of a substantially circular curve centred on the rotational centre.

8. The sensor transportation apparatus as claimed in claim 1 , wherein lateral extremities of the pair of skids and the orientation projections together define a curve extending circumferentially around a portion of the circumference of the elongate sensor assembly when the sensor transportation apparatus is connected to the elongate sensor assembly.

9. The sensor transportation apparatus as claimed in claim 8 , wherein the lateral extremities of the pair of skids and the orientation projections are curved lateral extremities, each curved lateral extremity extending circumferentially, partially around the circumference of the elongate sensor assembly.

10. The sensor transportation apparatus as claimed in claim 8 , wherein the lateral extremities of the pair of skids and/or the orientation projections are curved lateral extremities, each curved lateral extremity extending circumferentially, partially around the circumference of the elongate sensor assembly.

11. The sensor transportation apparatus as claimed in claim 10 , wherein a curvature of the curved lateral extremities of each skid of the pair of skids conforms to a curvature of a wall of the wellbore.

12. The sensor transportation apparatus as claimed in claim 8 , wherein the curve extending circumferentially around the portion of the circumference of the elongate sensor assembly extends a radial distance from the central axis of the elongate sensor assembly, and wherein the radial distance progressively decreases from a central orientation projection to each skid of the pair of skids.

13. The sensor transportation apparatus as claimed in claim 1 , wherein the pair of skids is arranged to have a greater spacing between the pair of skids than a spacing between the orientation projections.

14. The sensor transportation apparatus as claimed in claim 1 , wherein the pair of skids are positioned between 30° and 45° from a vertical plane through a longitudinal axis of the sensor assembly.

15. The sensor transportation apparatus as claimed in claim 1 , wherein the engagement structure is adapted to engage an exterior surface of the elongate sensor assembly.

16. The sensor transportation apparatus as claimed in claim 1 , wherein the engagement structure partially encloses the exterior surface of the sensor assembly without completely encircling the sensor assembly, or wherein the engagement structure is adapted for in-line connection to the sensor assembly.

17. The sensor transportation apparatus as claimed in claim 1 further comprising a guide device, the guide device comprising: a base adapted to engage an end of the elongate sensor assembly and a nose section having a tip which is offset from the longitudinal axis of the elongate sensor assembly when the guide device is engaged with said elongate sensor assembly.

18. The sensor transportation apparatus as claimed in claim 17 , wherein with the sensor transportation apparatus in the most stable position, an upward inclination of the nose section ensures the tip is elevated above the low side of the wellbore and is offset from and above the longitudinal axis of the elongate sensor assembly.

19. The sensor transportation apparatus as claimed in claim 17 , wherein the nose section is arranged to project from the base at a fixed angle to a longitudinal axis of the elongate sensor assembly when the guide device is engaged with the elongate sensor assembly.

20. The sensor transportation apparatus as claimed in claim 1 , wherein the elongate sensor assembly comprises a sampling tool oriented to take a sample from a high-side of the wellbore with the sensor transportation apparatus in the most stable position.

21. A guide device for guiding an elongate sensor assembly through a wellbore, the guide device comprising:

a pair of skids,

an orientation structure comprising at least three orientation projections, and

a nose section with a base attached to the orientation structure, the nose section having a tip which is offset from the longitudinal axis of the elongate sensor assembly when the guide device is engaged with the elongate sensor assembly,

wherein the orientation structure defines a form having a transverse outline which has a rotational centre, wherein the rotational centre is offset from a centre of mass of the elongate sensor assembly so that, in use, the elongate sensor assembly is oriented in a most stable position with the centre of mass of the elongate sensor assembly below the rotational centre and with the pair of skids oriented to slide along a low side of the wellbore, and with the tip of the nose section offset above the low side of the wellbore.

22. The guide device as claimed in claim 21 , wherein with the sensor transportation apparatus in the most stable position, an upward inclination of the nose section ensures the tip is elevated above the low side of the wellbore and is offset from and above the longitudinal axis of the elongate sensor assembly.

23. The sensor transportation apparatus as claimed in claim 21 , wherein the orientation structure comprises the pair of skids and each skid is a said orientation projection.