Method and apparatus for transmitting information between a salt-cavern and the surface of the ground

1. A method of transmitting information between a salt-cavern and the surface of the ground, said cavern being drilled in geological formation beds and being connected to the surface via an access borehole cased at least in part by metal tubes and presenting at least one safety valve, said method consisting in:

suspending a string of tools from a hanger system positioned in the access borehole downstream from the safety valve and in electrical contact with the metal tubes, said string of tools including at least one measuring device connected to the hanger system via a first segment of conductor cable and an information transceiver operating by means of waves and connected to the measuring device via a second segment of conductor cable, said transceiver being positioned in such a manner as to be in contact with structural means linked to the cavern; and

establishing coupling between the transceiver and the structural means, in order to enable information to be transmitted between the measuring device and the surface by propagating waves via the structural means.

2. A method according to claim 1 , wherein the transceiver is in contact with the bottom of the cavern and operates by electromagnetic waves propagating through geological formation beds.

3. A method according to claim 2 , wherein the coupling between the transceiver and the geological formation beds is electrical coupling that takes place by the presence of an electrolyte covering the bottom of the cavern.

4. A method according to claim 3 , wherein the electrolyte is electrically conductive brine present continuously at the bottom of the cavern.

5. A method according to claim 3 , wherein the electrolyte is added to the bottom of the cavern.

6. A method according to claim 1 , wherein the transceiver operates by mechanical waves.

7. A method according to claim 6 , wherein the coupling between the transceiver and the structural means is mechanical coupling that is performed by the presence of a vibrating element coupled to said structural means.

8. A method according to claim 7 , wherein the vibrating element is coupled to the bottom of the cavern or to the metal tubes.

9. A method according to claim 1 , wherein the measuring device is suspended at an arbitrary height in the cavern.

10. A method according to claim 1 , wherein the measuring device is suspended in the access borehole.

11. A method according to claim 10 , wherein the measuring device is provided with an insulating covering so as to avoid electrical contact with the metal walls of the access borehole.

12. A method according to claim 1 , wherein the step consisting in suspension the string of tools consists in:

a) connecting a transceiver to a conductor cable;

b) opening a safety vale and anti-blowout shutters of the access borehole;

c) lowering the transceiver down the access borehole to downstream from the safety valve and the anti-blowout shutters;

d) closing the anti-blowout shutters of the access borehole so as to block the conductor cable in order to hold the transceiver in suspension and seal the borehole;

e) cutting the cable upstream from the anti-blowout shutters;

f) connecting at least one measuring device to the conductor cable;

g) repeating steps b) to e) for the measuring device;

h) connecting the hanger system to the conductor cable; and

i) repeating steps b) to e) for the hanger system.

13. A device for implementing the method according to claim 1 , the device comprising a hanger system, at least one measuring device connected to the hanger system by a first segment of conductor cable, and an information transceiver connected to the measuring device by a second segment of conductor cable.