Abstract
The height of water-conducting fracture zones (WCFZs) is vital for the prevention of water, gas, and roof accidents in coal mines. However, its dynamic evolution law and maximum height are difficult to be obtained by traditional prediction methods, especially for conditions in which there is high overburden caving strength and a thick coal seam. Therefore, taking the 150,313 fully mechanized caving working face in Yingying Coal Mine as a background, according to the principle of optimized processes, a new predicting approach based on the Brillouin optical time-domain reflectometry (BOTDR) is proposed. Firstly, we estimated the height through empirical formula calculation, theoretical analysis, and similar model simulation tests. Secondly, we studied the optimized layout of optical cables in the overburden in detail for predicting the maximum height of the WCFZ and keeping the cables in good performance during field prediction. Thirdly, we researched and optimized the borehole parameters, optical fiber selection, and the special protection measures. Finally, we applied the aforementioned optimized outcomes in the field experiment to dynamically predict the height of the WCFZ. As a result of the field experiment, the distribution characteristics of optical fiber strain, the maximum height, and the evolution law of the WCFZ were obtained through the regular monitoring of fiber strain using BOTDR. The experiment demonstrated that its maximum height is consistent with the results studied indoors. The validation and feasibility of the approach proposed in this paper were verified via the aforementioned studies. The research in this paper has good reference value and important significance for predicting the height of the WCFZ using BOTDR in coal mines with similar geological and productive conditions.
Highlights
In China, coal is the major energy source and it accounts for about 68% of the total primary energy consumption [1]
Since Formulas (b) and (c) all belong to the Regulation of the 2017 edition, it was decided to take the average value of Formulas (b) and (c), and obtain 83.9 m; from the point of the key strata (KS) theory, it was shown that the hard K7 sandstone with a vertical distance of 85.66 m from the 15 coal seam is the primary key stratum (PKS), which is larger than the critical height of 73.1 m (7–10) M
It can be seen that compared with the results of empirical formula, key stratum discrimination height, and similar model test results, the maximum error is only
Summary
In China, coal is the major energy source and it accounts for about 68% of the total primary energy consumption [1]. There are several traditional methods that can be utilized for field prediction of the height of the WCFZ, such as drilling fluid loss measurement on the Earth’s surface [13], water leakage through boreholes underground [14], the electric resistivity method (ERM) [15], deep multi-point displacement detector through a borehole [16], microseismic monitoring [17], borehole photographing and borehole TV cameras [18], borehole core analysis [19], etc These traditional methods have made great contribution to the understanding of the WCFZ in coal mines. The new state-of-the art approach based on the optimized processes proposed in this paper is of great significance for the prediction of the height of WCFZ in coal mines with similar geological and productive conditions
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