Shear-Wave Porosity Logging in Sands

In this paper, the authors investigated the correlation between porosity and shear-wave velocity from acoustic logs in cored sand intervals. Data were collected in 13 wells with {gt}5,000 ft of core representing worldwide locations. Core porosities ranged from 0.02 to 0.38 at depths between 2,400 and 11,600 ft. Shear-wave velocities were obtained with Mobil's dipole logging tool, and porosities were obtained from standard core analysis. Our correlation data were obtained by averaging porosities and shear-wave travel times over intervals {ge}4 ft, the approximate resolution of our shear-wave tool. The authors excluded intervals in which the porosity or shear-wave travel time varied widely. The authors find a linear correlation between porosity and shear-wave travel time, provided we exclude clay-bonded sands such as those found along the U.S. gulf coast. The correlation coefficient is 0.91, about the same as that for compressional-wave data in the same intervals. These results are consistent with shear-wave data reported for ultrasonic laboratory measurements. Further comparison of our data with ultrasonic measurement shows evidence of dispersion effects.