Abstract:Formation damage of coastal aquifer refers to the flocculation and deposition of clay colloid during the displacement of salt water and fresh water. It has caused the pores blocked, and decreased the permeability of the aqueous medium. By using the flocculation experiments and sandcolumns experiments, the effects of ionic strength and cation valence on colloidal flocculation and deposition under different water chemical conditions have been studied. It is showed that when NaCl is regarded as the electrolyte, flocculation time drops quickly, and reduce from 82min to 39min, and the range of ionic strength is 0.032~0.034mol/L; when CaCl2 is regarded as electrolyte, the ionic strength is 0.006mol/L, the flocculation time only takes 6 minutes; the higher the calcium to sodium ratio, the faster the flocculation occurs. Sand columns experiments showed that the permeability of the medium will decrease when the ionic strength and the valence of the cation increases. When the ionic strength of NaCl electrolyte is 0.054mol/L and 0.017mol/L, the time for the permeability reduction by 20% is 15min and 50min respectively. For the same condition, when the ionic strength of CaCl2 electrolyte is 0.011mol/L, it takes only 5 minutes. The reason is that high ionic strength and valence cations can accelerate colloidal flocculation which cause the pores blocked. The results have potential practical application for reducing the formation damage of coastal aquifer.
