Acoustic monitoring of sediment‐pore fluid interaction

Abstract

Acoustic and chemical measurements were made on water‐saturated synthetic sediments undergoing diagenesis from uncompacted glass beads into a cemented glass bead, sandstone‐like material. The sediment‐water interaction was investigated as a function of time by monitoring the acoustic properties, water electrical conductivity, pH, and ion concentration. A reduction in the transmitted acoustic wave amplitude was correlated with a decrease in the total number of ions in the pore water. The lowest acoustic wave amplitude occurred when the ionic strength in the pore water had reached a minimum value. Calculation of the electrostatic potential showed that the force of repulsion between beads was strongest when the acoustic wave amplitude was at its minimum and the double layer electrostatic interaction potential between the beads was at a maximum value. At longer times the acoustic wave velocity of the transmitted wave increased as the cementation progressed. These results suggest that the chemical interaction between the pore fluid and grain alters the strength or stiffness of grain‐to‐grain contacts, which in turn alters the elastic modulus of the sediment frame. The important implications of this work are the potential use of acoustic or seismic techniques to monitor ion exchange between pore‐fluids and sediments in‐situ.