Study On Seismic Reflection Characteristics Of Coal Mine Goaf

With the continuous exploitation of underground coal resources,the number of coal mine gobs is increasing,and the area of goaf collapse is also growing.The mining and subsidence area not only seriously threatens the lives and property of the surrounding people,but also hinders the exploration and development of deep coal seams in the coal mines.Therefore,accurate identification of the mining subsidence area is of great significance for coal mine safety production and exploration of remaining resources.In this paper,the formation process and geological characteristics of coal mine goaf are systematically summarized.The propagation characteristics of seismic waves in the goaf medium are theoretically analyzed,which provides a reliable theoretical basis for the research.Then,according to the actual occurrence pattern of the goaf in Zhangji Coal Mine,the corresponding geological models are established,and forward modeling is carried out on these geological models,and the corresponding synthetic seismic records of the geological model are obtained.The obtained synthetic seismic records are analyzed on the single shot record and pre-stack time migration profiles,and the seismic reflection characteristics of the goaf in the same position are analyzed and compared.The general rules of the reflection characteristics of the goaf in phase,amplitude and frequency on the single shot record and the pre-stack time migration profile are summarized,so that the goaf can be accurately identified from the seismic time profile,its position is determined,and its range is delineated.To reduce the occurrence of coal mine safety accidents and avoid waste of resources.The goaf is recorded on the single shot: the continuity of the coal seam is degraded or even interrupted;the bottom of the coal seam is bent in the same phase,the frequency is reduced,the amplitude is increased;the delayed reflected wave and the delayed diffracted wave appear;There are many small,disorganized reflections in individual places.The goaf is represented by the offset profile: the continuity of the reflected wave in the same phase is degraded until it is missing;the reflected wave of the coal floor is bent in the same axial direction and becomes thicker;the delayed reflected wave and the abrupt point delay the occurrence of the diffracted wave;The appearance of short reflection waves at the interface between the drop zone and the crack band impedance.These wave field characteristics provide a theoretical basis for seismic exploration methods to detect goafs.