Peng Luo, Zhenyu Zhang, Lei Zhang, Xiaoqian Liu, Xiaobo Liu
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引用次数: 0
Abstract
The CO2 phase state changes during the long-term interaction with coal seams. A proper understanding of the influence of different CO2 phase states in water-bearing coal seams is of great significance in evaluating the leakage risk during CO2 sequestration. The evolution of fluid flow pathways in water-bearing coal subjected to the treatment of different CO2 phase states was investigated by using X-ray computed tomography (CT) technology, fractal dimension, and three-dimensional (3D) pore-scale flow modeling. The results show that the supercritical CO2 (ScCO2) treatment reduced the coal heterogeneity by 12.69% and increased the absolute permeability by 58.75%. Conversely, only 0.71% of coal heterogeneity reduction occurred after subcritical CO2 (SubCO2) treatment, increasing the absolute permeability by 24.91%. The reduction in the tortuosity fractal dimension after ScCO2 treatment was 2.69% larger than that of SubCO2 treatment, indicating that ScCO2 treatment was more favorable for improving the transport capacity of flow pathways. The pressure field distributions in the pore network model (PNM) were determined by coal heterogeneity and influenced by the number of flow pathways. The effect of ScCO2 treatment on the size, quantity, and location of preferential flow pathways in coal is more significant than that of SubCO2 treatment. Moreover, the proportion of preferential flow pathways in ScCO2-treated coal was less than 50%, much lower than that of the throats in PNMs. In contrast, the proportion of preferential flow pathways in SubCO2-treated coal was approximately 30% higher than that in ScCO2-treated coal. The distribution of preferential flow pathways also indicated that not all pores with larger radii participated in preferential flow. Furthermore, more than 50% of the pathways in the ScCO2-treated coal did not contribute to fluid flow, and could affect the stability of the coal seam.
期刊介绍：
Engineering geology is defined in the statutes of the IAEG as the science devoted to the investigation, study and solution of engineering and environmental problems which may arise as the result of the interaction between geology and the works or activities of man, as well as of the prediction of and development of measures for the prevention or remediation of geological hazards. Engineering geology embraces:
• the applications/implications of the geomorphology, structural geology, and hydrogeological conditions of geological formations;
• the characterisation of the mineralogical, physico-geomechanical, chemical and hydraulic properties of all earth materials involved in construction, resource recovery and environmental change;
• the assessment of the mechanical and hydrological behaviour of soil and rock masses;
• the prediction of changes to the above properties with time;
• the determination of the parameters to be considered in the stability analysis of engineering works and earth masses.
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