The primary interest set forth in the referenced article (“Resistivity-velocity transforms revisited” by Hacikoylu et al., published in TLE, August 2006) was to improve reconstruction of missing log data (e.g., velocity) from other reliable log measurements (e.g., resistivity). The authors considered an attempt to reconstruct a sonic curve from resistivity by Faust (1953). Faust's empirical equation related P-wave velocity, formation resistivity factor, and depth. The authors saw limitation in the use of Faust's equation and suggested improvements that would eliminate the deficiencies. In reading the article, one notices inconsistent definitions, improper use of equations relating rock property measurements, erroneous crossplots, and inconclusive analysis of data. Consequently, the authors fail to achieve the refinement of Faust's equation that they intended through their publication. In my conclusions, I have provided simpler equations relating resistivity with reciprocal velocity that account for geology and reservoir conditions.

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