Response Of Mobile Colloidal Particles’ Flocculation To Formation Damage In Coastal Area

At present sea water intrusion has become one of major environmental hazardproblems of coastal areas. For salt water intrusion problem, the most effective controland recovery method is to use fresh water to displace salt water,.But the process willbring about apparent formation damage.That is, when using fresh water to flood saltwater, permeability of aquifer will decrease gradually. The existing research showsthat release of colloid particles’ in aquifer is the main reason for the decrease ofpermeability. However relationships between particles’ dynamic flocculation andpermeability reduction is still unclear.Based on the systematic analysis of colloid, chemical and physical properties ofporous media, constant flow velocity experiments were explored. Dynamicflocculation of three different types of clay water chemical conditions. Effect of cationexchange on hydrodynamic flocculation of dispersed colloidal particles was alsoanalyzed using constant head test; Effect of valence of cations and flow velocity onhydrodynamic flocculation of dispersed colloidal particles was also studied. The mainresults are as follow:⑴With the same hydrochemical conditions, the speed of hydrodynamicflocculation of colloid is90%faster than that of hydrostatic flocculation;.Higherionic strength is, shorter the time for hydrodynamic flocculation is. Cation exchangeaccelerate the process of hydrodynamic flocculation and deposition.(2) The structure of porous meida itself will bring about a certain amount ofinterceptof colloid. The amount of montmorillonite intercepted in porous media is themost, followed by illite, That of kaoline is the lowest.(3) The effect of potassium ions on hydrodynamic flocculation of illite colloidalparticle is more significant than that of sodium ions. The effect of divalent cations onhydrodynamic flocculation of illite colloidal particles is more significant than that ofmonovalent cations. (4) Spatial distributions of different type of intercepted clays are not the same.The amount of intercepted kaoline in porous media decreases from inlet to outletwhile that of montmorillonite and illite increases from inlet to outlet. Theconcentration of effluent of three kinds of colloid will achieve a stable value in a shortperiod of time, which means that medium structure and suspension ionic strength andgranule concentration can achieve a dynamic balance.⑸The distribution of particle intercepted in porous media is clearly differentunder different flow regimes.When column is put horizontally, the amount of colloidintercepted is reduced from inlet to outlet. However,the results are just the oppositewhen column is put vertically. The effect of gravity to particle migration is significant,especially under high ionic strength, sedimentation of particles in porous media ismore apparent. In addition, velocity and colloid dynamic flocculation is inverselyrelated.