Research On Special Properties Of St.Peter Sandstone And Its Pillar Design

St. Peter sandstone can be used as the solid proppant in hyfraulic fracturing,which is the basic means for recovering gas trapped in rockmass. Research on itsproperties and pillar design is of great importance. Used XRD, SEM, Thin Section,Density, Size distribution, Uniaxial and Triaxial compressive tests to test theconsititution and structure, physical and mechanical properties of St. Peter sandstone;Developed a theoretical model for a quantitative evaluation of the effect of the fillinggrains on the porosity of the St. Peter sandstone, theoretically explained the porosityrange typically associated with the St. Peter sandstone and the basic cause of thisporosity variation, made it possible for a quick assessment of the sample strengthbased on size distribution information; Derived the stress distribution in Hertz stressfield, got the creck on the surface of the particles were mechanical fractures underhigh stress, which is Hertz fracture, overthrowed the present view of the surfacetexture was formed by transport, and thought that the cracks should be the results ofresults of the upper strata extrusion during the diagenetic process; With the idea ofStructure induced friction angle for rhombohedral packing, explained the reason whythe friction angle of St. Peter sandstone is17higher than other sandstone, andexplained the high dilation in a certain range; Based on the rhombohedral packing,proposed a strength estimate method, modified the Wilson theory, and got the widthof16m for pillar in Pattison mine. Proven by practice, the pillar can realize thepurpose of the rock stability control, and also increased the extraction ratio by10.7%compared with the original size.