Porosity estimation using a combination of Wyllie–Clemenceau equations in clean sand formation from acoustic logs

An equation relating acoustic travel time to the matrix and fluid times with the aim of quantifying sonic porosity in clean formations is introduced. However, this can be done by multiplying the well-known time average equation of Wyllie et al. [Geophysics 21 (1956) 41] by the acoustic formation factor equation of Raiga-Clemenceau et al. [Log Anal. (Jan.–Feb. 1988)] in an objective manner. This equation, which was satisfactorily tested among a wide variety of samples representing different lithologies, gives very close results with the measured values within an acceptable range of error. With the exception of core measurements and when no other porosity tools are available, the proposed equation is considered as a good predictor for estimating porosity, at least for the studied intervals considered here. What makes this equation more reliable and advantageous over another is that it integrates most of the parameters affecting porosity in a compatible way, which enhances the accuracy of estimating such parameter. Also, it gives reasonable values for rocks, which have a transit time between 40 and 120 μs/ft. Above this range, the usefulness of this equation must remain in doubt. Its successful application to real field data in the Gulf of Suez Basin of Egypt is also demonstrated.