Patent US 5,229,939

A borehole correction software of a multipole sonic well tool adapted to be disposed in a borehole determines a true, corrected value of shear wave slowness from a measured uncorrected shear wave slowness value by first building a look up table comprising hole diameter, measured synthetic shear wave slowness and correction factor, and using the table in a system including the look up table and a multiplier to determine a bias, which bias is subtracted from the measured uncorrected shear wave slowness to produce an output medium reflecting a true, corrected value of shear wave slowness. The measured uncorrected shear wave slowness values are input to the look up table. For a given hole diameter, the measured uncorrected shear wave slowness is matched to a measured synthetic shear wave slowness, and a value of correction factor is determined from the table. The correction factor is multiplied by the measured uncorrected shear wave slowness, via the multiplier, and a bias figure is determined. The bias figure is subtracted from the measured uncorrected shear wave slowness value, and a true, corrected shear wave slowness figure is the result. A plurality of the true, corrected shear wave slowness figures are determined using this technique and an output medium is produced which displays a log reflecting the true corrected shear wave slowness figures. This output medium may include a computer printout, the printout being given to a customer for his analysis of the characteristics of a formation within the borehole and the possibility of oil existing in the formation.