Inversion Of Travel Time For Velocity

Abstract

Common source velocities and borehole compensated (BC) estimates have been used to obtain formation velocity estimates from full waveform acoustic logs (Willis and Toksoz, 1982). With both of these methods the receiver separation of the tool dictates the depth resolution of the velocities determined. This paper presents a method to 1) increase the depth resolution of the velocity estimates, and 2) remove the effects of a changIng borehole radius upon the velocity estimates through formal inversion of arrival times and travel time moveouts. Results obtained by the inversion of full waveform acoustic log travel times appear quite promising. The velocity estimates on synthetic arrival times are slightly more noisy than those obtained using the standard BC technique. The most significant aspect of synthetic arrival times is that they generally appear to be unbiased. The BC technique is biased around formation boundaries and is especially biased for thin layers.