... : 12-18 mesh, 12-20 mesh, 16-20 mesh, 16-30 mesh, 20-40 mesh between 30-50 mesh, 40-60 mesh, 40-70 mesh and so on ... oil and gas, and propping the fractures not to be closed because of the released force when extracting oil by high ... closed fracturing, thereby to maintain the high conductivity of oil and ...