Simulation of coal microstructure characteristics under temperature-pressure coupling based on micro-computer tomography

The distribution of pore-fracture structure in coal directly affects the storage and migration characteristics of fluids. Simultaneously, under the condition of high buried depth, the coal structure is further changed by the temperature-pressure coupling. To study the pore size distribution of coal and the deformation characteristics of different pore-fracture structures under temperature-pressure coupling conditions, six different coal structure models are constructed using three-dimensional computer tomography reconstruction in this work. The box-counting algorithm is used to calculate the fractal dimensions of the pore-fracture structure and pore clusters in different pore sizes of coal. In the meantime, the fractal characteristics of the pore structure in different pore sizes are analyzed. Based on the coal structure model, a linear elastic deformation model under the temperature-pressure coupling is constructed. Moreover, the relationship of porosity and fractal dimension with the deformation of models is studied. The research results show that the porosity positively correlated with fractal dimension. The changes of pore volume fraction and fractal dimension in each pore size distribution range are consistent. Under the temperature-pressure coupling condition, both the model porosity and fractal dimension exhibit a quadratic function relationship with deformation. The deformation analysis of the three-dimensional models and two-dimensional cross-sections show that as the porosity and fractal dimension increase, the coal body deformation exhibits a trend of first decreasing and subsequent increasing. Low fractal dimension and high porosity could increase the model deformation. The research results can afford a theoretical basis for the study of coal structure characteristics under complex conditions.