a formation surrounding a borehole is traversed with a logging tool employing an acoustic transmitter and a pair of spaced - apart acoustic receivers . acoustic energy traveling through the formation from the transmitter to the receivers are detected . the energy of tube waves contained within the detected acoustic energy is measured . such measured tube wave energy is calibrated in response to measurements of tube wave energy ratio carried out in a zone of the formation having zero permeability . this calibrated tube wave energy is transformed into formation permeability in accordance with a measured relationship between permeability and tube wave energy ratio .