Sonde

1. An apparatus for deploying a sensor against a well casing, said apparatus comprising:

a) a sonde comprising an expandable and/or resilient C-shaped member and at least one sensor, the member having an annular configuration with a single gap that defines two ends facing each other, the member being compressible, or having been compressed, to bring its ends closer together;

b) means for supporting and locating the sonde inside the well prior to deployment: and

c) means for releasably compressing the C-shaped member so as to allow positioning of the sonde inside the well and subsequent deployment.

2. An apparatus according to claim 1 , which is such that deployment of said sonde is reversible so that said sonde may be removed.

3. An apparatus according to claim 1 , wherein the means for supporting the sonde prior to deployment comprise production tubing for insertion or inserted into the well casing.

4. A sonde comprising:

an expandable and/or resilient C-shaped member and at least one sensor, the member being compressible, or having been compressed, to bring its ends closer together;

means for supporting and locating the sonde inside the well prior to deployment: and

means for releasably compressing the C-shaped member so as to allow positioning of the sonde inside the well and subsequent deployment; and

wherein the means for releasably compressing the C-shaped member comprise a tool having a surface which co-operates with a surface of the C-shaped member to hold the C-shaped member in a compressed state.

5. An apparatus according to claim 2 , wherein the co-operating surfaces are shaped such that compression and decompression of the C-shaped member can be effected in a controlled gradual manner.

6. An apparatus according to claim 5 , wherein the C-shaped member has a chamfer at a circumference and the tool has a chamfered surface that acts on said chamfer to hold the C-shaped member in a compressed state.

7. An apparatus according to claim 5 , wherein the C-shaped member comprises one or more anchor portions and the tool comprises on or more pegs adapted to engage said anchor portion or portions.

8. A sonde comprising:

an expandable and/or resilient C-shaped member and at least one sensor, the member being compressible, or having been compressed, to bring its ends closer together;

means for supporting and locating the sonde inside the well prior to deployment: and

means for releasably compressing the C-shaped member so as to allow positioning of the sonde inside the well and subsequent deployment; and

the apparatus employing or being employable with fluid pressure derived from production tubing or a separate pressure source to effect deployment of the sonde.

9. A sonde comprising:

an expandable and/or resilient C-shaped member and at least one sensor, the member being compressible, or having been compressed, to bring its ends closer together;

means for supporting and locating the sonde inside the well prior to deployment: and

means for releasably compressing the C-shaped member so as to allow positioning of the sonde inside the well and subsequent deployment;

which is such that deployment of said sonde is reversible so that said sonde may be removed; and

wherein the compressing means are further adapted to compress and thus retrieve said sonde once deployed.

10. A sonde comprising:

an expandable and/or resilient C-shaped member and at least one sensor, the member being compressible, or having been compressed, to bring its ends closer together;

means for supporting and locating the sonde inside the well prior to deployment: and

means for releasably compressing the C-shaped member so as to allow positioning of the sonde inside the well and subsequent deployment;

wherein the means for supporting the sonde prior to deployment comprise production tubing for insertion or inserted into the well casing; and

wherein the sonde is at least partially supported, in its compressed stated, by one or more lugs associated with the production tubing.

11. An apparatus according to claim 10 , wherein the apparatus further comprises means for disengaging the lug or lugs from the sonde after the sonde has been deployed against the well casing.

12. An apparatus according to claim 11 , wherein the lug or lugs are disposed on a sleeve mounted on the production tubing, disengaging of the lugs from the sonde being effected by rotation of the sleeve about the tubing.

13. An apparatus according to claim 11 , wherein the means for releasably compressing the C-shaped member are further adapted, subsequent to the release of the C-shaped member and consequent deployment of the sonde, to disengage the lugs from the sonde.

14. A method of deploying a sonde against a well casing, said method comprising:

a) providing a sonde comprising an expandable and/or resilient C-shaped member and at least one sensor, the member having an annular configuration with a single gap that defines two ends facing each other;

b) compressing the C-shaped member thereby bring the ends closer to each other;

c) positioning the sonde at the desired location inside the well; and

d) releasing the C-shaped member thereby securing the sonde in place.

15. A method of deploying a sonde against a well casing, said method comprising:

a) providing a sonde comprising an expandable and/or resilient C-shaped member and at least one sensor, the member being compressible, or having been compressed, to bring its ends closer together;

b) compressing the C-shaped member;

c) positioning the sonde at the desired location inside the well;

d) releasing the C-shaped member thereby securing the sonde in place; and

wherein fluid pressure derived either from production tubing or a separate pressure source is used to deploy the sonde.

16. A method according to claim 15 , wherein such fluid pressure is used and controlled gradually to deploy said sonde gradually.