Topside interrogation using multiple lasers for distributed acoustic sensing of subsea wells
A distributed acoustic system (DAS) may include an interrogator that includes two or more lasers, a pulser module disposed after and connected to each of the two or more lasers, a wavelength division multiplexer (WDM), wherein each of the pulser modules are connected to the WDM as inputs, and a downhole fiber attached to the WDM as an output and wherein the downhole fiber includes at least one sensing fiber. A method for increasing a sampling frequency may include identifying a length of a downhole fiber connected to an interrogator, generating and launching a light pulse from each of the two or more lasers the pulser module, and delaying an output from the pulser module into the downhole fiber by k N seconds, where k is a pulse repetition interval of the pulser module and N is equal to the two or more lasers.
1. A distributed acoustic system (DAS) comprising:
two or more lasers;
a pulser module disposed after and directly connected to each of the two or more lasers;
a wavelength division multiplexer (WDM), wherein the pulser module is disposed between the two or more lasers and the WDM;
a distal circulator connected to the WDM by a fiber optic cable; and
a downhole fiber attached to the distal circulator as an output and wherein the downhole fiber comprises at least one sensing fiber.
2. The DAS of claim 1 , further comprising an Erbium doped fiber amplifier (EDFA) disposed between the WDM and the distal circulator.
3. The DAS of claim 1 , wherein the pulser module delays a light pulse for each of the two or more lasers into the downhole fiber by
k
N
seconds, where k is a pulse repetition interval of the pulser module and N is equal to a number of lasers that are at least a part of the interrogator.
4. The DAS of claim 1 , further comprising a photo detector assembly connected to the distal circulator by a second fiber optic cable.
5. The DAS of claim 4 , further comprising a second EDFA disposed between the distal circulator and the photo detector assembly.
6. The DAS of claim 5 , further comprising the WDM disposed between the second EDFA and the photo detector assembly.
7. The DAS of claim 6 , further comprising an interferometer disposed between the second EDFA and the WDM.
8. The DAS of claim 7 , further comprising two or more parse devices disposed between the WDM and the photo detector assembly.
9. The DAS of claim 8 , further comprising an information handling system connected to the photo detector assembly.
10. A method for increasing a sampling frequency comprising:
identifying a length of a downhole fiber connected to a distal circulator,
generating and launching a light pulse for two or more lasers;
multiplexing the light pulse for the two or more lasers with a wavelength division multiplexer (WDM), wherein each of the two or more lasers are connected to a pulser module as inputs, and wherein the WDM is disposed on a fiber optic cable between the pulser module and the distal circulator; and
delaying the light pulse from the pulser module for each of the two or more lasers into the downhole fiber by
k
N
seconds, where k is a pulse repetition interval of the pulser module and N is equal to the number of lasers that are connected to the pulser module.
11. The method of claim 10 , further comprising an Erbium doped fiber amplifier (EDFA) disposed between the WDM and the distal circulator.
12. The method of claim 10 , further comprising a photo detector assembly connected to the distal circulator by a second fiber optic cable.
13. The method of claim 12 , further comprising a second EDFA disposed between the distal circulator and the photo detector assembly.
14. The method of claim 13 , further comprising an interferometer disposed between the second EDFA and the photo detector assembly.
15. The method of claim 14 , further comprising the WDM disposed between the second EDFA and the photo detector assembly.
16. The method of claim 15 , further comprising an interferometer disposed between the second EDFA and the WDM.
17. The method of claim 16 , further comprising two or more parse devices disposed between the WDM and the photo detector assembly.
18. The method of claim 17 , further comprising an information handling system connected to the photo detector assembly.
19. The method of claim 18 , wherein the information handling system is configured to identify one or more regions of the fiber optic cable for which backscatter is received.