Study On The Microstructure Fractal Characteristics Of Dense Sandstone

The microstructure of dense sandstone is important for evaluating the hydrogeological conditions of mining areas,preventing water damage accidents in coal mines,and ensuring safe production in coal mines.In this paper,three North Chinatype coal mines,Gequan mine,Gaohe coal mine in Lu'an mine and Tunlan mine,were used as research objects.Using digital core techniques such as cast thin section experiments,scanning electron microscopy and other techniques,combined with fractal theory,the pore permeability characteristics of sandstone were studied,and the relationships between pore phase and solid phase fractal characteristics,porosity,pore size,grain size and fractal dimension of dense sandstone were revealed,as well as the influencing factors of permeability of dense sandstone.The main contents of the paper include the following.1.The collected cores were measured for porosity and permeability,and the average values of porosity for Gequan,Lu'an and Tunlan mines were obtained as 4.06%,1.442% and 3.915%,respectively;the average values of permeability were 0.0137 m D,0.0548 md and 0.021 m D,respectively;the experimental identification results of the cast thin section showed that the sandstone samples were dominated by rock chip sandstone,with gap-filling material The results of the cast thin section experiments show that the sandstone samples are mainly clastic sandstone,with high content of filler,relatively dense,and mainly developed microporosity.2.Scanning electron microscope experiment.SEM and Image Pro Plus software were used to acquire rock images,and the perimeter and area of the pore and solid phases were calculated and measured.The fractal characteristics of the pore and solid phases were analyzed using fractal theory combined with SEM images,and the fractal determination criterion was extended from the pore phase to the solid phase.The pore phase and solid phase characteristics of the samples were investigated by the box dimension method of fractal theory,and it was found that the bilogarithmic coordinate maps were straight lines.Based on the box dimension method with the constraint of fractal medium criterion,it is found that the solid phase of the sample satisfies the fractal distribution,while the pore phase does not satisfy the fractal distribution.3.The permeability of the sample was calculated by introducing the diameter and the average hydraulic radius of the particles into the Ergun-Wu equation.The comparison of the measured permeability with the calculated permeability has little error,which indicates that this method is feasible to calculate the permeability.The thesis has 47 figures,13 tables and 88 references.