Response characteristic of in-seam seismic wave field for collapse column in symmetrical medium

Abstract

Collapse columns which can usually destroy the integrity of strata are widespread in the Carboniferous and Permian coalfields for North China type. The incubation and development process of collapse column could change the mechanical property and acoustic feature of surrounding rock. Rock wave velocity was tested under uniaxial loading and the relationship of wave velocity and stress was obtained before plastic deformation. Based on the physical property parameters of rock and coal, homogeneous medium for three symmetrical layers was established. For the full-wave-fields forward modeling, elastic wave equations were analyzed through finite difference method. Wave field snapshot, plane-wave seismogram and frequency dispersion curve were obtained after analysis for the collapse column in the model. In-seam seismic wave field was inversed through velocity analysis and CT analysis of energy attenuation coefficient. The effect on inversion result was researched for different physical property parameters of collapse column and observing system parameters. The research results showed that seismic wave field was decayed with the increase of propagation distance. In-seam seismic wave signal was weakened or even disappeared when the collapse column is encountered. When the wave velocity of the collapse column is larger than that of the surrounding rock or smaller than that of the coal seam, an obvious diffraction in-seam wave is formed and the Airy phase pulsates. When the wave velocity of the collapse column is less than that of the coal seam, it is characterized by low speed anomaly, and the collapse column with low speed or high speed produces obvious energy attenuation anomaly. When the field observation system is arranged, the gun spacing and channel spacing can be selected as 20 m.

Keywords

• symmetrical medium
• collapse column
• in-seam seismic wave
• velocity analysis
• attenuation coefficient