Mechanism of fracture network characteristics on extraction efficiency in low-permeability NAPL-contaminated formations
Hydraulic fracturing,which can improve substance transport,offers an effective solution to the challenge of remediating low-permeability contaminated formations.This study employed COMSOL Multiphysics,a large-scale multi-physics coupled simulation software,to simulate hydraulic fracturing-assisted extraction of non-aqueous phase liquids(NAPLs)in low permeability formations.The influence of different fracture network characteristics on the extraction efficiency was analyzed.The results demonstrate that the extraction efficiency can be significantly enhanced by the fracture network,with an improvement rate over 42％and the removal rate of pollutants increases with fracture thickness,length,and permeability,with the fracture permeability being the primary influencing factor.Through coupling analysis of fracture network parameters,it was observed that when the ratio of fracture permeability(kf)to matrix permeability(k)exceeds 100,the removal rate of pollutants initially increases,then fluctuates before declining.Additionally,the optimal removal effect was achieved with a fracture length of 1.5 m.This phenomenon can be attributed to the substantial attenuation of the promoting effect of fracture length after the removal of pollutants from the upper layer of the fracture.Hence,locating the fracture network in the lower part of the contaminated formation is more advantageous for pollutant removal.
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