Research on the critical conditions for clay particle release during saline aquifer freshening process

Abstract

Water sensitivity phenomenon occurs during saline aquifer freshening process in seawater intrusion area, and clay particles released in the phenomenon can damage the infiltration capacity of the aquifer. In order to find out the factors and mechanisms for clay particle release, laboratory column infiltration experiments simulating saline aquifer freshening process were designed to measure the critical conditions (critical flow velocity, critical salt concentration and critical ionic strength) and force analysis for clay particle according to DLVO electric double layer theory was employed to illustrate the mechanisms for particle release. The research results showed that critical flow velocity for clay particle release is influenced by salt concentration of injecting solution. When salt concentration of injecting solution is very high, clay particles are not released, indicating that there does not exist a critical flow velocity in this situation. As salt concentration of injecting solution decreases, particles start to be released. The critical salt concentration for clay particle release is 0.052 mol L−1 in our work, which was determined by a constant-flux experiment for stepwise displacement of high concentration NaCl solution. The critical ionic strength for clay particle release decreases as Ca2+ molar content percentage of the mixed solution of NaCl and CaCl2 increases following the first-order exponential decay equation y = 0.0391e−0.266x + 0.0015.