DEVELOPMENT OF A TECHNIQUE FOR RESEARCHING THE OPENING WIDTH AND TORTULUSITY OF A CRACK IN A COAL CORE ACCORDING TO ELECTRON MICROSCOPY DATA

Abstract

The article discusses issues related to the determination of filtration-capacitance properties of cracks in coal core based on the analysis of images of polished sections taken with a scanning electron microscope. Using numerical modeling of gas dynamics equations, the features of the steady-state laminar gas flow regime in a single crack are studied. It has been shown that the decrease in the speed of gas flow passing through a crack in coal is significantly influenced by its geometric features. Gas consumption primarily depends on the opening width of the crack and its tortuosity. Other factors, such as roughness, its type and wedge shape, make a smaller contribution to the amount of gas pressure loss along the length of the crack. A simple modification of the Boussinesq equation, taking into account the contribution of each factor determined by the geometry of the crack, allows us to describe the process of gas flow in a real crack. Using the example of studying polished sections prepared from a coal core drilled from a large piece of coal from the Permyakovsky section of the Karakan coal deposit using electron microscopy and subsequent digital processing of the resulting images using numerical methods for modeling gas flow, it is shown that the greatest resistance to gas movement in a crack is provided by its tortuosity. A method has been developed for determining the opening width, tortuosity and roughness of the crack faces, which allows both to determine the listed geometric parameters of the crack and to calculate the gas permeability along it. If necessary, it is possible to apply the technique to predict gas permeability in a coal core, but for this it is necessary to calculate the closure of the crack faces due to the imposition of rock pressure on the boundary of the core surface.