Well logging with autonomous robotic diver

1. A logging apparatus for use in a well, the logging apparatus comprising:

multiple segments, wherein the multiple segments are directly coupled to each other, wherein an articulation device controls a relative orientation between adjacent segments, wherein the articulation device is operative to change the relative orientation between the multiple segments to dispose the logging apparatus in a helical shape;

at least one sensor that senses a well parameter; and

at least one buoyancy control device, wherein the logging apparatus displaces in the well in response to a change in a buoyancy of the logging apparatus.

2. The logging apparatus of claim 1 , wherein the sensor and the buoyancy control device are included in at least one of the segments.

3. The logging apparatus of claim 1 , further comprising at least one engagement device that engages a well surface.

4. The logging apparatus of claim 3 , wherein the engagement device comprises a magnetic device.

5. The logging apparatus of claim 3 , wherein the engagement device comprises a motorized wheel.

6. The logging apparatus of claim 1 , wherein the sensor comprises an ultrasonic sensor.

7. A method of logging in a subterranean well, the method comprising:

disposing at least one logging apparatus in the well, wherein the at least one logging apparatus comprises:

multiple segments, wherein the multiple segments are directly coupled to each other, wherein

an articulation device controls a relative orientation between adjacent segments

at least one sensor; and

at least one buoyancy device;

displacing the logging apparatus through the well in response to a change in the buoyancy of the logging apparatus;

changing the relative orientation between the multiple segments to arrange the multiple segments in a helical shape against an inner surface of the well; and

taking measurements with the at least one sensor while the logging apparatus maintains the helical shape against the inner surface at a selected position in the well.

8. The method of claim 7 , wherein the changing the relative orientation further comprises the logging apparatus changing from a linear configuration to a helical configuration in the well.

9. The method of claim 7 , further comprising changing relative orientations between adjacent ones of the segments in the well.

10. The method of claim 7 , further comprising changing a torque applied to the logging apparatus, thereby changing a helical configuration of the logging apparatus.

11. The method of claim 7 , wherein the installing further comprises attaching the logging apparatus to a cementing plug.

12. A well system, comprising:

at least one logging apparatus disposed in a wellbore, the logging apparatus comprising:

multiple segments, wherein the multiple segments are directly coupled to each other, wherein an articulation device controls a relative orientation between adjacent segments, wherein the articulation device is operative to change the relative orientation between the multiple segments to dispose the logging apparatus in a helical shape;

at least one sensor that senses a well parameter; and

at least one buoyancy control device, wherein the logging apparatus displaces in the wellbore in response to a change in a buoyancy of the logging apparatus,

and

wherein the at least one logging apparatus maintains the helical shape at a selected position against an inner surface of the wellbore.

13. The well system of claim 12 , wherein the segments further include at least one engagement device that engages a surface in the wellbore.

14. The well system of claim 12 , wherein the well parameter is selected from the group consisting of temperature and ultrasonic waves.

15. The well system of claim 12 , wherein the segments further include a communication device.