Effect of water inclusions on charge transport and polarization in porous media

Wideband dielectric spectroscopy measurements (100 Hz to 10 GHz) were carri ed out on different microporous systems (including sintered glass filters, sandstone and carbonate rocks) saturated with brine (electrolytic water sol ution) and a hydrocarbon oil at different relative fractions. Three main co ntributions were singled out in the dielectric speetra: low frequency dispe rsion (LFD) effects (< 100 kHz) related to long range ionic transport and d ependent on the connectivity of the water phase; Maxwell-Wagner-Sillars (MW S) polarization effects (100 kHz to 1 GHz), essentially controlled by the s hape of the water inclusions; and high-frequency effects (>1 GHz) due to sh ort-range ion transport and related to specific pore surface. For each anal yzed system, oil-wet (o-w) and water-wet (w-w) samples were obtained by che mical treatment of the pore surfaces. Systematic differences were observed in the electrical response on varying wettability land so the respective di stribution of the fluids in the pore space). Parameters such as the loss ta ngent value, the strength and the exponent of the LFD power law, as well as the characteristic time and strength of the MWS relaxation were good indic ators of wettability. Results were discussed by using some standard models that account for the pore wettability effects on dielectric spectra. A new method for wettability determination of reservoir rocks from both laborator y and borehole electric measurements was presented.