Seismic monitoring and analysis of excessive gas emissions in heterogeneous coal seams

Abstract

Uncontrolled and excessive gas emissions pose a serious threat to safety in underground coal mining. In a recently completed research project, a suite of monitoring techniques were employed to assess the dynamic response of the coal seam being mined to longwall face advance at Coal Mine Velenje in Slovenia. Together with continuous monitoring of gas emissions, two seismic tomography measurement campaigns and a microseismic monitoring programme were implemented at one longwall top coal caving panel. Over 2,000 microseismic events were recorded during a period of four months. Over the same period, there also was a recorded episode of relatively high gas emission in the same longwall district. In this paper, a detailed analysis of the processed microseismic data collected during the same monitoring period is presented. Specifically, the analysis includes the spatial distribution of the microseismic events with respect to the longwall face advance, the magnitude of the energy released per week and its temporal evolution. Examination of the spatial distribution of the recorded microseismic events has shown that most of the microseismic activity occurred ahead of the advancing face. Furthermore, the analysis of the gas emission and microseismic monitoring data has suggested that there is a direct correlation between microseismicity and gas emission rate, and that gas emission rate tends to reach a peak when seismic energy increases dramatically. It is believed that localised stress concentration over a relatively strong xylite-rich zone and its eventual failure, which was also identified by the seismic tomography measurements, may have triggered the heightened microseismic activity and the excessive gas emission episode experienced at the longwall panel monitored.

Numerical modelling of microseismicity associated with longwall coal mining

“…Fig. 2a presents an example of the spatial distribution and the energy level, represented by the size of individual circles, of the microseismic events recorded at Coal Mine Velenje over one production week (Si et al, 2015a). The corresponding histogram of the magnitude of the recorded energy is presented in Fig.…”

“…In a previous study by the authors (Si et al, 2015a), it was observed that the range of seismic energy released spanned by up to four orders of magnitude (from 10 2 to~10 6 J).…”

“…The geophones were all located in the same level of the LTCC panel, and only microseismic activities that occurred close to this horizontal plane were accurately identified. In addition, time-lapse active seismic tomography over a 100 m × 141 m area ahead of the advancing face was also performed on the same panel (Si et al, 2015a).…”

Coupled Effects of Moisture Content and Inherent Clay Minerals on the Cohesive Strength of Remodelled Coal

“…In underground coal mining systems, coal wall spalling, gas emissions, and unexpected roof falling are serious disasters increasing the economic cost and challenging the security of coal production, especially when the coal seam is soft and weak [1][2][3]. The stability of soft coal seam is difficult to control due to the relatively low mechanical properties.…”

An Experimental Investigation on the Relationship between MS Frequency Response and Coal and Gas Outburst

“…Many researchers suggested using gas pressure, coal bed stresses, and methane concentration parameters based on these characteristic pieces of information to predict CGOB disasters. The main contactless monitoring and early warning methods to predict the CGOB disasters include electromagnetic radiation (EMR) method [15][16][17][18], acoustic emission (AE) method [19,20], and microseismic (MS) method [21]. Compared with AE and EMR, MS inversion technology exhibits advantages in source inversions, monitoring range, and signal connotation aspects over a large size monitoring range [22][23][24].…”