A study of pore structure,pore fractal feature and permeability of unconsolidated sand

Pore structure of unconsolidated medium is an important influence on fluid migration.Unconsolidated quartz sand samples are consolidated with epoxy resin and are used to produce thin sections.The parameters of pore structure are obtained from these sections with image processing method.The fractal models of pore structure are used to analyze the fractal feature of unconsolidated porous medium,and the permeability of porous medium is measured and calculated.The results indicate that there is linear dependence among porosity,pore size and grain diameter.The correlation coefficient between porosity and grain diameter is-0.9765,while the correlation coefficient between pore size and grain diameter is 0.9966.In the double logarithmic coordinate system of lnε-lnN（ε）,the data points of side length of square（i.e.,ε） and total square numbers（i.e.,N（ε）） of having pores are approximately in a line,and the fractal dimensions of pore distribution are very close for different samples.Moreover,in the double logarithmic coordinate system of lnr-lnN（r）,the data points of pore sizes（i.e.,r） and total pore numbers（i.e.,N（r）） of pore size that are greater than r are analyzed with the subsection regression method.The results of subsection regression method can reflect the practical situation of pore structure.There are high corresponding relationships between the fractal dimension of pore structure and the fractal dimension of grain diameters.The permeability measured by experiment is 5.19×10-5mm2,which is 5.75×10-5mm2 when calculated with the fractal dimension of bigger grain diameters.The two values are very close.Fractal dimension of grain diameters can be used to calculated the permeability of porous medium.