Methods for Locating A Cement Sheath in A Cased Wellbore

A distributed acoustic wave detection system and method is provided. The system may include a fiber optic cable deployed in a well and configured to react to pressure changes resulting from a propagating acoustic wave and an optical source configured to launch interrogating pulses into the fiber optic cable. In addition, the system may include a receiver configured to detect coherent Rayleigh noise produced in response to the interrogating pulses. The CRN signal may be used to track the propagation of the acoustic waves in the well. Such capability allows the location of the cement sheath, as well as measuring the bonding of cement to at least a casing string at least partially surrounded by a cement sheath.