The macromolecular structure of tectonically deformed coals (TDC) may be determined by the deformation mechanisms of coal. Alterations of the macromolecular structure change the pore structure of TDC and thereby impact physical properties such as porosity and permeability. This study focuses on structure and properties of TDC from the Huaibei and Huainan coal mining areas of southern North China. Relationships between the macromolecular structure and the pore structure of TDC were analyzed using techniques such as X-ray diffraction, high-resolution transmission electron microcopy, and the low-temperature nitrogen adsorption. The results indicated that the directional stress condition can cause the arrangement of basic structural units (BSU) more serious and closer. And, the orientation is stronger in ductile deformed coal than in brittle deformed coal. Tectonic deformation directly influences the macromolecular structure of coal and consequently results in dynamic metamorphism. Because the size of BSU in brittle deformed coal increases more slowly than in ductile deformed coal, frictional heating and stress-chemistry of shearing areas might play a more important role, locally altering coal structure under stress, in brittle deformed coal. Strain energy is more significant in increasing the ductile deformation of coal. Furthermore, mesopores account for larger percentage of the nano-scale pore volume in brittle deformed coals, while mesopores volume in ductile deformed coal diminishes rapidly along with an increase in the proportion of micropores and sub-micropores. This research also approved that the deformations of macromolecular structures change nano-scale pore structures, which are very important for gas adsorption and pervasion space for gas. Therefore, the exploration and development potential of coal bed methane is promising for reservoirs that are subjected to a certain degree of brittle deformation (such as schistose structure coal, mortar structure coal and cataclastic structure coal). It also holds promise for TDC resulting from wrinkle structure coal of low ductile deformation and later superimposed by brittle deformation. Other kinds of TDC suffering from strong brittle-ductile and ductile deformation, such as scale structure coal and mylonitic structure coal, are difficult problems to resolve.

Different mechanisms of deformation could make different influence on inner structure and physical properties of tectonically deformed coal (TDC) reservoirs. This paper discusses the relationship between macromolecular structure and physical properties of the Huaibei-Huainan coal mine areas in southern North China. The macromolecular structure and pore characteristics are systematically investigated by using techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), and low-temperature nitrogen adsorption method. The results suggest that under the directional stress, basic structural units (BSU) arrangement is closer, and the orientation becomes stronger from brittle deformed coal to ductile deformed coal. Structural deformation directly influences the macromolecular structure of coal, which results in changes of pore structure. The nanoscale pores of the cataclastic coal structure caused by the brittle deformation are mainly mesopores, and the proportion of mesopores volume in ductile deformed coal diminishes rapidly. So the exploration and development potential of coalbed gas are good in reservoirs such as schistose structure coal, mortar structure coal and cataclastic structure coal. It also holds promise for a certain degree of brittle deformation and wrinkle structure coal of low ductile deformation or later superimposed by brittle deformation.

To study the effect of different deformation mechanisms on the chemical structure of anthracite coals and further understand the correlation between changed chemical structures and coal and gas outburst, ten groups of sub-high-temperature and sub-high-pressure deformation experiments were performed. All samples maintained primary structure, which were collected from the Qudi Mine in the southern Qinshui Basin of China. The samples were analyzed by ultimate analysis, Vitrinite Reflection (VR), Fourier Transform Infrared spectroscopy (FTIR), and Raman spectroscopy both before and after deformation experiments for contrasting. The results showed that the VR values of all samples after experiments were significantly higher than before experiments, which suggested that the metamorphism degree of anthracite coals was increased by deformation. The results also indicated that both temperature and strain rate had significant effects on the chemical structure of anthracite coals. At a high strain rate of 4×10 5 s 1 , the deformation of the samples was mainly brittle in which the mechanical energy was transformed mainly into frictional energy. In this situation, all samples developed several distinct fractured surfaces and the change of chemical structures was not obvious. On the contrary, with the decrease of the strain rates, the ductile deformation was dominated and the mechanical energy was mainly transformed into strain energy, resulting in the accumulation of deformation energy confessed by increasing quantity of dislocation and creep in the coal's interior nucleus. The absorption in the aromatic ring groups increased; otherwise the absorption in the aliphatic structures and ether oxygen groups decreased rapidly. During these experiments, CO was collected from two experimental samples. The number of aromatic rings and the structure defects within the two generated gas samples increased and the degree of molecular structure orders decreased. anthracite coal, deformation experiment, VR, Vitrinite Reflection Indicating surface (VRI), secondary structure defect Citation: Xu R T, Li H J, Hou Q L, et al. 2015. The effect of different deformation mechanisms on the chemical structure of anthracite coals. Science China: Earth Sciences,

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