Research On The Experiment Of Physical Clogging During The Restoration Of Saline Aquifer

This research takes the method of extracting salt water while injecting freshwaterduring the restoration process of the underground salt water in Research Area. Therecharge water comes from the surface water and rain-flood water, and it is inevitablethat clogging phenomenon occurs during the recharge process, especially the physicalclogging. The most typical type of physical clogging is caused by suspended particles,which is also the most common clogging type that happens in the recharge system.This article mainly adopts lab sand column experiments to have research on thephysical clogging of aquifer medium under different conditions, including differentparticle size of the porous media, different suspended particles concentration,different initial seepage velocity and different mineralization of saturating water. Bycomparing the change of particle size of the media between before and after therecharge, the transfer-aggradation law of suspended particles in the aquifer mediumcan be discovered. By measuring the media’s permeability coefficient of differenttime, the clogging situation can be quantitatively showed. Moreover, this article alsodiscusses preventive measures and treatment of physical clogging. From the research,we can get conclusions as follows:（1） The percolation coefficient experiences a large-scale decline in the initialperiod of recharge, and the decreasing amplitude of percolation coefficient graduallydeclines with the extension of injection time,and finally becomes steadier and thedecreasing amplitude of permeability of different parts of sand column （K₁、K₂、K₃、K₄） declines in proper order. The suspended particles can be easily intercepted at thesurface of the sand column when the particle size of the medium is small, thus leadingto severe decrease of the surface permeability. Longer percolation distance and greaterimpact on the permeability of the medium’s deeper layer will take place during therecharge process when the particle size and porosity of the medium are bigger and at the meantime the permeability of the medium will experience a sharper decline as forthe whole column.（2） During the recharge process with the water of different suspended particlesconcentration, the permeability of each part of the sand column drops gradually.Under the condition of the same suspended particles concentration of recharge water,the permeability declines greater when closer to the surface. With the suspendedparticles concentration increases from50mg/L to200mg/L, permeability of each partof the column decreases much greater. With the increase of the suspended particlesconcentration and injection time and decrease of the percolation distance, relativepermeability coefficient drops obviously.（3） The smaller of the size of suspended particles, the further of the percolationdistance and the deeper depth of the ‘sharp decline area of permeability’. That is tosay, the greater of the decreasing amplitude of percolation coefficient of the deep layer,the decrease of the equivalent percolation coefficient will be much more obvious. Onthe contrary, the suspended particles can be easily intercepted at the surface when itssize is bigger and it only causes the surface percolation coefficient decline by a largemargin, and at the same time has small influence on the deep layer’s percolationcoefficient, as a result the deep layer’s percolation coefficient decreases slightly, thuscausing a light effect on the permeability of the whole sand column.（4） With the increasing of the seepage velocity, the distinction of the value ofK₁under different velocity is inconspicuous, and it will ultimately drop to3%approximately. However, the decreasing amplitude of the value ofK₂,K₃andK₄experience continuous increase. When the seepage velocity is relatively high,‘thepercolation coefficient decline area of the sand column’ will be larger and thedecreasing amplitude of the deep layer’s permeability will undergo a consecutive riseat the same time. And under the condition of relatively low seepage velocity, cloggingbasically happens at the surface layer. Besides, with higher seepage velocity, it turnsout that the transfer distance of suspended particles becomes longer and the placewhere suspended particles be intercepted becomes deeper. （5） When the mineralization of saturating water is relatively low, thepermeability of the sand column experience a slow decline and tiny decreasingamplitude, and it will be stable at about80%⁹0%in the end, compared with theinitial permeability. When the mineralization of saturating water is relatively high, thepermeability of the sand column experience a sudden decline at the beginning ofrecharge and the decreasing amplitude has a positive correlation with salinity, andthere will be large amount of clay particles being released in the outflow water, whichcan be considered as the phenomenon of water sensitivity.（6） Generally, the prevention of physical clogging is often based on controllingthe source of recharge water and engineering design. As for the treatment of surfacephysical clogging, cleaning the silt seam existed at the surface of aquifer medium canbe of great help to the increase of surface permeability, but has marginal effect on thepermeability change of the deep medium. With regard to the aquifer medium withserious water sensitivity, the simple cleaning work does no benefit to solve theclogging problem, especially the clogging happened in the internal aquifer medium.And it sounds difficult to solve the internal clogging problems of the medium, so anounce of prevention is commonly worth a pound of treatment as for physicalclogging.