The coal measure strata formed in the late Paleozoic era underwent tectonic movements on several occasions, leading to the development of a range of fold structures in the strata as a result of highly interlayered gliding and shearing deformation. In addition, brittle ductile tectonic coals were widely distributed in the reservoir, constituting one of the primary causes of coal-gas outbursts in Chinese mines. This indicates a strong connection between shear deformation and such outbursts. In this study, structural geology, gas geology, and rock mechanics are all taken into consideration to investigate the controlling effects of the fold structure formation process on coal thickness and tectonic coal formation. Numerical simulation, based on the stress test data, was deployed to identify the stress distribution law adjacent to fold structures under the modern stress field. Additionally, the mechanical mechanism underpinning coal-gas outbursts near the fold structure was determined by making a comparison with the distribution law relating to such outbursts. The results demonstrate that the formation and evolution of the fold structure not only form the material basis of outbursts but also control their power source. During the fold formation process, interbed sliding and shearing between strong and weak rock strata were caused by differences in the mechanical properties of the coal bed and rock layer, resulting not only in a change to the local thickness of the coal seam but also in its deformation and structural alteration. Interbed shearing and local stress concentration, caused by the coal gangue, led to coal damage and the development of layered tectonic coal of consistent thickness, simultaneously improving its ability to adsorb gas and providing the material basis for coal-gas outbursts. This reduced the seam's capacity to resist such events. The conditions for these outbursts are created 1 State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Henan Polytechnic University), Jiaozuo, P.R. China 2 Institute of Gas Geology, Henan Polytechnic University, Jiaozuo, P.R. by the sudden desorption of excess gas as a result of formation pressure release during coal mining and the widespread distribution of tectonic coal. Under the modern tectonic stress field, the stress distribution characteristic is controlled by the fold structure shape; and because of the aforementioned differences in the mechanical properties of the coal bed and rock layer, the interlayer deformation is asynchronous. This causes shear stress concentration within a specific range of the anticline's two wings. This concentration zone happens to be exactly aligned with that of coal-gas outbursts, meaning that shear stress concentration is considered to be both the power source for and main cause of the region's outbursts.

No abstract

No abstract

The correct understanding of the occurrence law of coalbed gas (CBG) is the premise of gas disaster prevention, outburst risk prediction, and gas exploitation. The factors affecting gas occurrence in different gas-geology units are different, so the correct division of gas-geology units is the foundation for studying the occurrence law of CBG. In view of this, this paper defined the division principle of gas-geology units. A gas-geology unit is an area with the same gas-geology characteristics. Based on the division of tectonic units, gas-geology units can be divided by integrating the differences of in situ stress, geological factors, and gas distribution of each tectonic unit. Then, taking the Guhanshan mine field in the Jiaozuo coalfield as an example, the analysis method of the occurrence law of CBG based on gas-geology units was expounded. Taking the EW section, NE section, and their extension lines of the Tuanxiang fault as the boundary, the Guhanshan mine field was divided into four tectonic units, and the factors affecting the gas occurrence of each tectonic unit were analyzed. Finally, according to the difference of the bedrock thickness and the CBG distribution in the four tectonic units, combined with the fracture development degree of the coal seam, surrounding rock, and the development degree of deformed coal, the Guhanshan mine field was divided into three gas-geology units, and their occurrence law of CBG was analyzed.