Dispersion features of transmitted channel waves and inversion of coal seam thickness
- 95 Downloads
In-seam seismic survey currently is a hot geophysical exploration technology used for the prediction of coal seam thickness in China. Many studies have investigated the relationship between the group velocity of channel wave at certain frequency and the actual thickness of exposed coal beds. But these results are based on statistics and not universally applicable to predict the thickness of coal seams. In this study, we first theoretically analyzed the relationship between the depth and energy distribution of multi-order Love-type channel waves and found that when the channel wave wavelength is smaller than the thickness of the coal seam, the energy is more concentrated, while when the wavelength is greater than the thickness, the energy reduces linearly. We then utilized the numerical simulation technology to obtain the signal of the simulated Love-type channel wave, analyzed its frequency dispersion, and calculated the theoretical dispersion curves. The results showed that the dispersion characteristics of the channel wave are closely related to the thickness of coal seam, and the shear wave velocity of the coal seam and its surrounding rocks. In addition, we for the first time realized the joint inversion of multi-order Love-type channel waves based on the genetic algorithm and inversely calculated the velocities of shear wave in both coal seam and its surrounding rocks and the thickness of the coal seam. In addition, we found the group velocity dispersion curve of the single-channel transmitted channel wave using the time–frequency analysis and obtained the phase velocity dispersion curve based on the mathematical relationship between the group and phase velocities. Moreover, we employed the phase velocity dispersion curve to complete the inversion of the above method and obtain the predicted coal seam thickness. By comparing the geological sketch of the coal mining face, we found that the predicted coal seam thickness is in good agreement with the actual thickness. Overall, adopting the channel wave inversion method that creatively uses the complete dispersion curve can obtain the shear wave velocities of the coal and its surrounding rocks, and analyzing the depth of the abruptly changed shear wave velocity can accurately obtain the thickness of the coal seam. Therefore, our study proved that this inversion method is feasible to be used in both simulation experiments and actual detection.
KeywordsLove-type channel wave Energy distribution High-order dispersion Coal seam thickness prediction
This work was supported by the Major Project on Natural Science Study of the Department of Education, Anhui Province (No. KJ2016SD17), the Scientific Research Activity Funding Project for Leaders in Academics and Technology in Anhui Province (No. 2016D079), and the National Natural Science Foundation (No. 41604082). Special thanks are given to the anonymous reviewers for their assistance, comments, and suggestions.
- Buyuk E, Zor E, Karaman A (2017) Rayleigh wave dispersion curve inversion by using particle swarm optimization and genetic algorithm. In: EGU general assembly conference. EGU general assembly conference abstractsGoogle Scholar
- Du W, Peng S (2010) Coal seam thickness prediction with geostatistics. Chin J Rock Mech Eng 29(s1):2762–2767Google Scholar
- Ji GZ, Cheng JY, Zhu PM (2011) Numerical simulation of seam love type channel-wave and analysis on dispersion features [J]. Coal Sci Technol 39(6):106–109. https://doi.org/10.13199/j.cst.2011.06.112.jigzh.001 CrossRefGoogle Scholar
- Ji GZ, Cheng JY, Zhu PM et al (2012) 3-D numerical simulation and dispersion analysis of in-seam wave in underground coal mine. Chin J Geophys 55(2):645–654. https://doi.org/10.6038/j.issn.0001-5733.2012.02.028 CrossRefGoogle Scholar
- Lei F, Wang W, Li S, Yao X, Teng J, Gao X (2017) Research on the channel wave field characters of goaf in coal mine and its application. In: Di Q, Xue G, Xia J (eds) Technology and application of environmental and engineering geophysics. Springer Geophysics. Springer, SingaporeGoogle Scholar
- Liu TF, Pan DM, Li DC, Li HS (1994) In-Seam seismic exploration. China University of Mining & Technology Press, Xuzhou, pp 51–52Google Scholar
- Räder D, Schott W, Dresen L et al (1985) Calculation of dispersion curves and amplitude-depth distributions of love channel waves in horizontal-layered media. Geophys Prospect 33(6):800–816. https://doi.org/10.1111/j.1365-2478.1985.tb00779.x CrossRefGoogle Scholar
- Wang W, Xue G, Gao X et al (2016c) Channel wave tomographic imaging method and its application in detection of collapse column in coal [C]. In: International conference on environment and engineering geophysics & summit forum of Chinese Academy of Engineering on engineering science and technologyGoogle Scholar