The function of pressure for coalification is a long-term controversial issue, and the main cause is that the strata pressure and the tectonic stress were confused, which are two different actions of "pressure". The former benefits the physical coalification but retards the chemical coalification, whereas the latter may not only affect the physical structure of coal but also promote its chemical composition changes. In accordance with the organic molecule evolution of coal, there are two kinds of basic mechanisms of the influence of the tectonic stress on the chemical coalification: the tectonic stress degradation and the tectonic stress polycondensation. The stress degradation mechanism is a process of that, when the tectonic stress acted on the large molecule of coal in the form of mechanical force or kinetic energy, some chemical bonds of low decomposed energy, such as aliphatic side-chain and oxygenic functional groups, were broken up and then were degraded into free radicals of less molecular weight, and finally escaped from coal in the form of liquid organic matter (hydrocarbon). The stress polycondensation is considered that, under the control of the anisotropic tectonic stress, the condensed aromatic nucleus trend to be parallel arranged and to be enhanced through rotating or displacing of aromatic rings, the basic structural unit of coal (BSU) increases by directional development and preferential stack. X-ray diffraction (XRD), Fourier transformation infrared microspectroscopy (FTIR), and rock pyrolysis analysis (Rock-eval) were employed to study the deformed coal series and the non-deformed coal series. The results showed that, compared with the non-deformed coal, the deformed coal exhibits particular characteristics: weaker aliphatic absorbance peak and stronger aromatic absorbance peak, lower pyrolysed hydrocarbon yield, and more increscent BSU. The concepts of stress degradation mechanism and stress polycondensation mechanism presented here would not deny the dominant function of the temperature in coalification, but emphasize the "catalysis" of the tectonic stress in coalification.coalification, pressure factor, tectonic stress degradation, tectonic stress polycondensation, tectonically deformed coal Coal, a kind of organic rock, is very sensitive to geological environment factors, such as temperature, pressure, etc. Various tectonic-thermal events during the geological evolution process would lead to coal producing a series of physical, chemical, structural, and tectonic changes. The research of coalification factors is one of the basic works for coal resources evaluation, coalbed methane development and coal-mining gas prevention [1,2] . Organic macro-molecules in coal is composed of condensed aromatic nucleus of a plenty of side chains and functional groups [3] . They belong to non-crystal state materials that are lack of order in a long distance while better ordered in a short distance [4] . Coalification is a process of rich

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Pulverized coal is one of the main controlling factors constraining the capacity of coal-bed methane wells during CBM drainage. The characteristics of pulverized coal can be used to identify the sources of the pulverized coal particles and to develop reasonable means of controlling pulverized coal output. Using light transmission microscopy, laser particle size testing, X-ray diffraction, reflection polarized optical microscopy, and scanning electron microscopy with energy dispersive X, the characteristics of pulverized coal collected during CBM drainage in the Hancheng block were analyzed for concentration, particle size, composition, and morphology. These traits were used to identify the sources of pulverized coal. The results showed that coal body structure (structural damage) was a primary control factor of pulverized coal output. The sizes of the pulverized coal particles tended to be around 100 µm. The main components of pulverized coal were vitrinite and clay minerals. The pulverized coals were divided into groups based on their columnar, flaky, or granular morphology. Columnar pulverized coal may involve the formation of the native structure coal or the fragmented coal that later sustains erosive damage. Flaky pulverized coal may be produced by the flaking of scaled coal or leaf coal. In this way, granular pulverized coal may be produced from granulated coal. Therefore, the morphology of the pulverized coal was found to be related to its coal body structure and to late mechanical destruction.

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The occurrence of coal-bearing strata in a variety of coal-bearing basins of China is characterized by late tectonic deformation and remarkable spatial and geochronologic differences. The main controlling factors, which determine the tectonic framework of coalfields, include the geodynamic environment, tectonic evolution, deep structures, tectonic stress, and lithologic combination of the coal measures. The Chinese continent has experienced multi-stage tectonic movements since the Late Paleozoic. The spatial and temporal heterogeneity of its continental tectonic evolution, the complexity of its basement properties, and its stratigraphic configurations control the tectonic framework of its coalfields’ present complex and orderly patterns. The concept of coal occurrence structural units is proposed in this paper and is defined as the structural zoning of coal occurrence. China’s coalfields are divided into five coal occurrence structural areas, and the structural characteristics of the coalfields in five main coal occurrence areas throughout the country are summarized. Based on the analysis of the relationship between the structure characteristics and occurrence of coal in these coalfields, the coal-controlling structures are divided into six groups: extensional structural styles, compressional structural styles, shearing and rotational structural styles, inverted structural styles, sliding structural styles, and syn-depositional structural styles. In addition, the distribution of coal-controlling structural styles is briefly summarized in this paper.