a method and system for well logging provide indications of the characteristics of fluid flow behind pipe . an acoustic listening device is positioned within a pipe in proximity to suspected fluid flow behind the pipe . acoustic energy resulting from the fluid flow is detected and separated into at least two frequency groups or ranges ; the first comprising acoustic energy of relatively low frequency and the second comprising acoustic energy of relatively higher frequency . the relative distribution of acoustic energy between the two frequency groups provides an indicator of the nature of the fluid flow behind the pipe .