Sensor transportation apparatus and guide device

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 wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly, and

an orientation structure comprising the pair of wheels and an orientation projection extending between the pair of wheels, lateral extremities of the pair of wheels and the orientation projection together defining 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, wherein a rotational centre of the curve is offset from a central axis of the elongate sensor assembly when the sensor transportation apparatus is connected to the elongate sensor assembly, and

wherein a rotational axis of the pair of wheels is above the central axis of the elongate sensor assembly when the sensor transportation apparatus is connected to the elongate sensor assembly and the sensor transportation apparatus is substantially horizontal.

2. The sensor transportation apparatus as claimed in claim 1 , wherein the lateral extremities of the pair of wheels and the orientation projection are curved lateral extremities, each curved lateral extremity extending circumferentially, partially around the circumference of the elongate sensor assembly.

3. The sensor transportation apparatus as claimed in claim 1 , wherein the lateral extremities of the pair of wheels and/or the orientation projection are curved lateral extremities, each curved lateral extremity extending circumferentially, partially around the circumference of the elongate sensor assembly.

4. The sensor transportation apparatus as claimed in claim 3 , wherein a curvature of the curved lateral extremities of the pair of wheels is the same as a curvature of the curved lateral extremity of the orientation projection, and wherein the curvature of the curved lateral extremities of the wheels and the orientation projection is centred at the rotational center.

5. The sensor transportation apparatus as claimed in claim 1 , wherein the pair of wheels comprises a first wheel and a second wheel, and

the first wheel has a first curved lateral extremity extending circumferentially around a first portion of the elongate sensor assembly, and

the second wheel has a second curved lateral extremity extending circumferentially around a second portion of the elongate sensor assembly.

6. The sensor transportation apparatus as claimed in claim 1 , wherein the orientation projection has a third curved lateral extremity extending circumferentially around a third portion of the elongate sensor assembly.

7. The sensor transportation apparatus as claimed in claim 1 , wherein the pair of wheels comprises a first wheel and a second wheel, and

the first wheel has a first curved lateral extremity extending circumferentially around a first portion of the elongate sensor assembly, and

the second wheel has a second curved lateral extremity extending circumferentially around a second portion of the elongate sensor assembly, and

the orientation projection has a third curved lateral extremity extending circumferentially around a third portion of the elongate sensor assembly.

8. The sensor transportation apparatus as claimed in claim 1 , 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 portion of the orientation projection to each wheel.

9. The sensor transportation apparatus as claimed in claim 1 , wherein the curve extending circumferentially around the portion of the circumference of the elongate sensor assembly is a circular curve.

10. The sensor transportation apparatus as claimed in claim 1 , wherein the rotational axis of the pair of wheels passes through the rotational centre of the curve extending circumferentially around the portion of the circumference of the elongate sensor assembly.

11. The sensor transportation apparatus as claimed in claim 1 , wherein the offset between the rotational centre of the curve and the central axis of the elongate sensor assembly causes the sensor transportation apparatus to be oriented in a most stable position with the central axis of the elongate sensor assembly below the rotational centre of the curve.

12. The sensor transportation apparatus as claimed in claim 1 , wherein the orientation structure and an offset between the rotational axis of the pair of wheels and the central axis of the elongate sensor assembly makes the sensor transportation apparatus unstable when connected to the elongate sensor assembly to cause the sensor transportation apparatus and elongate sensor assembly to orientate to a position in which the rotational axis of the pair of wheels is above the central axis of the elongate sensor assembly.

13. The sensor transportation apparatus as claimed in claim 1 wherein the pair of wheels are mounted on stub axles.

14. 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 elongate sensor assembly.

15. The sensor transportation apparatus as claimed in claim 1 , the sensor transportation apparatus comprising:

a guide device, having 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.

16. The sensor transportation apparatus as claimed in claim 15 , wherein the guide device comprises:

a base 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, and

wherein the nose section with said tip is arranged to project away from the base at a fixed angle to a longitudinal axis of the elongate sensor assembly when the guide device is engaged with said elongate sensor assembly.

17. A method for conveying an elongate sensor assembly through a wellbore, the method comprising:

connecting a sensor transportation apparatus to the elongate sensor assembly, the sensor transportation apparatus comprising a pair of wheels arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly, and an orientation structure comprising the pair of wheels and an orientation projection extending between the pair of wheels, wherein:

lateral extremities of the pair of wheels and the orientation projection together defining a curve extending circumferentially around a portion of the circumference of the elongate sensor assembly, and

a rotational centre of the curve is offset from a central axis of the elongate sensor assembly, and

wherein a rotational axis of the pair of wheels is above the central axis of the elongate sensor assembly when the sensor transportation apparatus is substantially horizontal, and

conveying the sensor transportation apparatus and the elongate sensor assembly through the wellbore with the sensor transportation apparatus causing the sensor transportation apparatus and elongate sensor assembly to orientate to a position in which the rotational axis of the pair of wheels is above the central axis of the elongate sensor assembly.

18. The method as claimed in claim 17 , wherein, wherein the lateral extremities of the pair of wheels and/or the orientation projection are curved lateral extremities, each curved lateral extremity extending circumferentially, partially around the circumference of the elongate sensor assembly.

19. The method as claimed in claim 17 , wherein the curve extending circumferentially around a portion of the circumference of the elongate sensor has a radius that is smaller than a radius of the wellbore.

20. 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 wheels comprising a first wheel and a second wheel arranged to rotate about an axis of rotation substantially perpendicular to a longitudinal axis of the sensor assembly when the transportation apparatus is connected to the sensor assembly, and

an orientation structure comprising the first and second wheels and an orientation projection extending between the first and second wheels,

the first wheel comprising a first curved lateral extremity extending circumferentially around a first portion of the elongate sensor assembly, and

the second wheel comprising a second curved lateral extremity extending circumferentially around a second portion of the elongate sensor assembly, and

the orientation projection comprising a third curved lateral extremity extending circumferentially around a third portion of the elongate sensor assembly,

the first, second and third curved lateral extremities together defining 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, wherein a rotational centre of the curve is offset from a central axis of the elongate sensor assembly when the sensor transportation apparatus is connected to the elongate sensor assembly, and

wherein a rotational axis of the pair of wheels is above the central axis of the elongate sensor assembly when the sensor transportation apparatus is connected to the elongate sensor assembly and the sensor transportation apparatus is substantially horizontal.