Pseudovelocity logs are generated by computer from short-normal resistivity logs by using the relation TT = A + B (R)^{<fr>-1</>C</fr>}. Given the resistivity value R, the transit time TT can be computed if the empirical constants A, B, and C are known. Although two distinct geologic provinces are present in Indiana (the Cincinnati arch and the Illinois basin), the same sets of constants are applicable throughout the state.

For wells drilled with a mud range of 2 to 5 ohm-m, visual comparison of the pseudovelocity logs with actual continuous-velocity logs (CVLs) shows close correlation in form. In addition, calculation of the cumulative transit times from a datum to a given depth yields values for pseudovelocity logs and CVLs that compare within 6 percent. The method is most successful if applied to the stratigraphic section below the freshwater--salt water contact.

The constants A, B, and C are based on computations from selected depths on resistivity logs and CVLs. Our studies now indicate that R and TT values averaged over regular 10-ft (3 m) intervals also yield reasonable A, B, and C values for computation and eliminate the need for the user to make decisions about what depths are appropriate for selecting R and TT values.