Wireless communication system for monitoring of subsea well casing annuli

1. A method for monitoring at least one condition in at least one of a plurality of casing annuli in a subsea hydrocarbon production system, the subsea hydrocarbon production system comprising a wellhead housing mounted at the upper end of a well bore and a number of concentric well casings extending from the wellhead housing through the well bore, including an innermost casing through which a hydrocarbon fluid is produced, and the plurality of casing annuli being defined between successive ones of the wellhead housing and the well casings, the method comprising:

sensing at least a first condition at a first location in a first casing annulus;

generating a first data signal at the first location which is indicative of the first condition;

transmitting the first data signal from the first location to a second location either outside the wellhead housing or inside the innermost casing;

receiving the first data signal at the second location; and

transmitting the first data signal from the second location to a remote location at which the first condition is configured to be monitored;

wherein the first data signal is transmitted from the first location to the second location using near-field magnetic induction (NFM) communications signals.

2. The method of claim 1 , further comprising:

generating an interrogation signal at the second location;

transmitting the interrogation signal from the second location to the first location; and

receiving the interrogation signal at the first location;

wherein the step of transmitting the first data signal from the first location to the second location is performed in response to the step of receiving the interrogation signal at the first location; and

wherein the interrogation signal is transmitted from the second location to the first location using NFM communications signals.

3. The method of claim 1 , further comprising:

sensing at least a second condition at a third location in a second casing annulus, the first location being between the second location and the third location;

generating a second data signal at the third location which is indicative of the second condition;

transmitting the second data signal from the third location to the second location;

receiving the second data signal at the second location; and

transmitting the second data signal from the second location to the remote location;

wherein the second data signal is transmitted from the third location to the second location using NFM communications signals.

4. The method of claim 3 , wherein the step of transmitting the second data signal from the third location to the second location comprises transmitting the second data signal directly from the third location to the second location.

5. The method of claim 3 , wherein the step of transmitting the second data signal from the third location to the second location comprises:

transmitting the second data signal from the third location to the first location;

receiving the second data signal at the first location; and

transmitting the second data signal from the first location to the second location.

6. The method of claim 5 , wherein the step of transmitting the second data signal from the third location to the second location is performed using a multi-hop signal transmission technique.

7. The method of claim 3 , further comprising:

generating an interrogation signal at the second location;

transmitting the interrogation signal from the second location to the first and third locations;

receiving the interrogation signal at the first location; and

receiving the interrogation signal at the third location;

wherein the steps of transmitting the first data signal from the first location to the second location and transmitting the second data signal from the third location to the second location are performed in response to the steps of receiving the interrogation signal at the first location and receiving the interrogation signal at the third location, respectively; and

wherein the interrogation signal is transmitted from the second location to the first and third locations using NFM communications signals.

8. The method of claim 7 , wherein the steps of transmitting the interrogation signal from the second location to the third location and transmitting the second data signal from the third location to the second location comprise transmitting the interrogation signal directly from the second location to the third location and transmitting the second data signal directly from the third location to the second location.

9. The method of claim 7 , wherein the steps of transmitting the interrogation signal from the second location to the third location and transmitting the second data signal from the third location to the second location comprise:

transmitting the interrogation signal from the second location to the first location;

receiving the interrogation signal at the first location;

transmitting the interrogation signal from the first location to the third location;

transmitting the second data signal from the third location to the first location;

receiving the second data signal at the first location; and

transmitting the second data signal from the first location to the second location.

10. The method of claim 5 , wherein the steps of transmitting the interrogation signal from the second location to the third location and transmitting the second data signal from the third location to the second location are performed using a multi-hop signal transmission technique.