Abstract：Having referred to Byun's method for the inversion of anisotropic-medium parameter. I apply least-square inversion technique to the inversion of first arrival time of zero-offset VSP data so as to solve for interval velocity and formation depth. Formula for correctly calculating formation parameter is given. This method is characterized by (1) making similarity analysis after iterative inversion, (2) using iterative inversion result as the initial value of the similarity analysis and (3) solving for correct formation parameters with the use of least mean square error. Theoretical and practical results prove this method effective. The similarity analysis can partly remove the accumulative error caused in calculating the parameters of overlying formations, thus improving inversion accuracy.
