Topside interrogation using multiple lasers for distributed acoustic sensing of subsea wells

A method comprising:

• generating and launching one or more light pulses of a first optical frequency from at least one laser into a fiber optic cable, wherein the light pulses traverse the fiber optic cable to a sensing fiber;
• forming a backscatter signature based on at least two combinations of the light pulses in the sensing fiber, wherein the backscatter signature traverses from the sensing fiber to a photodetector assembly;
• determining one or more phases of the backscatter signature, wherein determining the one or more phases comprises:
• shifting the first optical frequency to a second optical frequency with an acousto-optic modulator;
• taking one or more measurements of the backscatter signature and the second optical frequency;
• and
• comparing the one or more measurements with an information handling system to find a heterodyne beat signal,
• determining a seismic energy of the backscatter signature based at least in part on the one or more phases;
• and
• identifying a strain along the fiber optic cable based at least in part on the seismic energy of the backscatter signature.