The research of coal seam gas pressure and initial gas emission characteristics of borehole

Abstract

Gas pressure is one of the major factors to characterize the outburst danger of coal seams. Generally, the process of gas pressure determination is complicate and cannot ensure the accuracy of results, which may cause a wrong identification of outburst danger. This paper discussed and revealed a positive correlation between initial gas emission and gas pressure, which provides a new approach to identify the outburst danger by initial gas emission. Through theoretical analysis and numerical simulation, the liner equation of gas pressure and initial gas emission was deduced. Laboratory experiments under adsorption and desorption of CO2 and N2 were performed using coal samples from Weishe coal mine. The data of initial gas emission under different gas pressure were recorded, and the fitting curves were obtained. The results show a positive correlation between initial gas emission and gas pressure, and the curve of N2 was below the CO2. Especially, while the adsorption gas pressure was under 0.663 and 0.675 MPa, the difference of corresponding initial gas emission was only 0.01 L/s, which indicates the high degree of correlation. The results validated the theoretical and practical feasibility to identify the coal and the gas outbursts through initial gas emission.

Experimental research on adsorption characteristics of N2, CH4, and CO2 in coal under different temperatures and gas pressures

“…By comparing the gas adsorption ratio under different pressures after normalization, the adsorption ratio of CO 2 was more extensive than that of N 2 and CH 4 . High pressure increased the number of molecules and the unit space of molecular energy and made gas molecules more easily collide with the coal surface 41,42 …”

A calculation method of gas emission zone in a coal mine considering main controlling factors

“…The larger the emission intensity, the larger the influence range of gas content in the coal body forming the roadway side per unit time 33 , 34 . The larger the permeability coefficient of coal seam, the smaller the gas flow resistance, the faster the flow and the greater its volume 35 . The section of roadway determines the exposed area of coal body and affects the failure of coal seam, the redistribution of secondary stress and the expansion and development of fracture channels.…”

Discrimination Method of Gas Pressure Measurement in Coal Seams: Physical Experiment and Model Development

“…34 The following physical assumptions are introduced: (1) The coal matrix can be simplified to the continuum model. (2) The gas content absorbed by the coal body conforms to the Langmuir equation. (3) The coal matrix is isotropic, and the gas flow in the coal matrix conforms to Fick's law.…”

“…The measurement of gas pressure in coal seams is an important work in mine safety production. , Accurate measurement of coal seam gas pressure is of great significance for the prediction and early warning of coal and gas outbursts, the study of the gas desorption and emission law, and the evaluation of the coal seam gas content. − At present, the direct method to measure gas pressure in coal seams is one of the most common methods. By drilling and sealing in the coal seam, a closed gas chamber is formed, and the gas in the adjacent coal seam is constantly desorbed and diffused into the gas chamber.…”