REARRANGEMENT OF FINE PARTICLES IN POROUS-MEDIA CAUSING REDUCTION OF PERMEABILITY AND FORMATION OF PREFERRED PATHWAYS OF FLOW - EXPERIMENTAL FINDINGS AND A CONCEPTUAL-MODEL

The rearrangement of matrix configuration due to the redistribution of clay particles was studied by introducing different suspensions into porous media. Clay (kaolinite) with low CEC (cation exchange capacity) and small flocs of high CEC clay (smectite) accumulated in regions of slow flow. In some experiments this was followed by rapid accumulatio n in regions of high velocity, impairing flow to a considerable degree . Clay with high CEC formed more voluminous structures which could bri dge over a passage and impair the flow. In either case, whether small or large units of clay are involved, the final flow occurred mainly th rough open, preferred pathways. Such processes of redistribution and a ppearance of flow pathways may occur in subsurface porous media aquife rs where forced gradients exist (e.g. in aquifers near the perforation of pumping wells and in places where large quantity of water are natu rally or artificially recharged and in producing gas and oil fields).