1. A method comprising: estimating a formation boundary depth from well log data, said well log data providing formation attribute data for a plurality of azimuth angles, wherein said formation boundary depth is estimated for each of said azimuth angles; estimating effective volume of investigation (EVOI), using a programmed computer, and using the relationship 
 EVOI≡ΔD 2 ·Δh·Δφ to determine an effective shift in height (Δh) of a formation boundary surface associated with said formation boundary depth, where ΔD is an effective depth of investigation and Δφis an azimuthal aperture; and refining said formation boundary depth estimate using said effective shift in height (Δh).