A method of abandoning a wellbore can include obtaining a first sample data set within a wellbore, wherein the first sample data set is a sample of an acoustic signal originating within the wellbore; determining a plurality of frequency domain features of the first sample data set; identifying a fluid flow location within the wellbore using the first plurality of frequency domain features; setting a barrier at or above the fluid flow location; obtaining a second sample data set above the barrier, wherein the second sample data set is a sample of an acoustic signal originating within the wellbore above the barrier; determining a second plurality of frequency domain features of the second sample data set; and identifying that a fluid flow rate or flow mechanism at the fluid flow location has been reduced or eliminated and/or identifying another fluid flow location using the second plurality of frequency domain features.