Research On High-quality Interval Of The Observing Magnification On Microscopic Pore Structure Characteristics Of Sandstones Under The Scanning Electron Microscope

The paper takes thick sandstone aquifers existing between or above coal seams of the North China Carboniferous-Permian coalfield as the main research object,based on understanding and familiarizing the geological background of the study area,sampling cores in sandstone aquifer groups on the top and bottom floors of the main coal seam for five typical mines(Malan,Tunlan,Liyazhuang,Jining,Gequan),totally 32 sandstone cores were obtained by using exploration drilling as the main method.In order to explore the high-quality interval of microscopic pore structure characteristics of sandstone under the scanning electron microscope,guided by mine geology,hydrogeology and fractal theory,a variety of analytical testing techniques were applied comprehensively such as casting thin-plate identification,CT three-dimensional reconstruction,and scanning electron microscope(SEM).Combined with existing research results on porosity and permeability of tight sandstone,the main conclusions are as follows:1.The results,according to laboratory measurements,show that the sandstone cores collected in the five mining areas have extremely low porosity and permeability.2.Observed the casting thin-plate by polarized light microscopy,lithology is unequal-grained sandstone of fine-grained sandstone and siltstone.The main colors are off-white and black-gray and the main component is rock cuttings,followed by quartz and feldspar.Sandstone granularity is mainly fine-grained,with a small amount of medium-grained.Interstitial material is high,mainly including kaolinite,siderite,illite.3.CT scan results show that sandstone samples are mostly small pores with poor connectivity and do not support liquid or gas circulation.4.Using the “slit island method” model,applying Avizo,Image Pro Plus software to extract the area and perimeter from micropore structure of sandstone SEM image.The theoretical permeability of sandstone micropore structure was calculated based on Poiseuille formula and Darcy seepage theory.The results show that the high-quality interval of microscopic pore structure characteristics of sandstone under the scanning electron microscope is between ×200 and × 1000,and the ×500 scale is closest to the measured permeability,with about 2.1% error.That means this scale has a strong self-similarity between local and global reactions.At this scale,it is concluded that there is a strong correlation between the theoretical permeability and the measured permeability,which provides certain help for the water-prevention work of the roof in the mining area.The thesis has 50 figures,5 tables,and 75 references.