Does wettability influence seismic wave propagation in liquid-saturated porous rocks?

Abstract

In order to evaluate the effects of different fluids, we measured the P and S wave speeds through a series of synthetic epoxy-bonded carbonate composites with porosities from 21.9 to 31.5 per cent and saturated with air, with kerosene and with brine. These observed speeds were converted to the saturated bulk and shear moduli and compared to predictions made using Biot and Gassmann formulations. The observed bulk moduli agreed with those calculated for both kerosene and brine saturation as did the high frequency shear modulus under kerosene saturation. The observed shear modulus under water saturation, however, was significantly lower than the prediction. After excluding the currently known mechanisms of shear weakening, we suspect this disparity may be due to variations in the wetting of the epoxy that coats the pores surfaces. The kerosene completely wets this surface while the brine is only weakly hydrophilic with a wetting angle of 73.6?. At the molecular scale, this means that Stoke's no-slip boundary condition may not always apply as has been more recently demonstrated by many researchers in other disciplines such as microfluidic engineering but the implications for wave propagation in liquid-saturated rocks have not been considered.