Complex impedance measurements have been performed on 14 shaly sand samples, Berea sandstone, and Ottawa sand-bentonite packs in a frequency range of 10 Hz to 10 MHz, using both the two- and four-electrode techniques. Measurements have been conducted at an effective radial stress varying from ambient pressure to 4000 psi for brine-saturated oil-wet and water-wet samples. The dielectric permittivity is found to correlate with the clay volume fraction, the cation exchange capacity, and electrochemical potential of the rock samples and to depend strongly on the salinity of the brine used. Stress and wettability are shown to have a small influence on the dielectric constant of fully brine-saturated rocks. A lower critical frequency is found to characterize the geometry of the pore space. Empirical correlations between the dielectric constant, frequency, permeability, cation exchange capacity, and porosity are presented for the shaly sands used in this study. These correlations provide a means of estimating important petrophysical parameters such as the permeability and the clay content from a nondestructive complex impedance sweep of shaly sands fully saturated with brine.

Read More: http://library.seg.org/doi/abs/10.1190/1.1443650