Analysis Of Seismic Response Characteristics Of Mine Goaf

The shallow coal seams in the main coal distribution areas of our country have left a large number of goaf after long-term mining.The coal mine goaf and the accumulated water and gas of the old kiln are often the cause of the collapse,gas outburst and water permeable accidents in the adjacent coal seam mining,and the subsidence or collapse of the coal mine goaf is all kinds of large ground.The construction of the project and the environment have caused great influence.Due to the formation age,burial depth,space structure,surrounding rock conditions,caving,filling and water accumulation,the physical properties of the goaf are very different.The coal mining background is not clear and the geological environment is complex in many areas.It is generally regarded as a world problem to detect the coal mine goaf..At present,geophysical methods for detecting goaf are mainly classified into seismic and electromagnetic methods.In order to explore the ability of seismic reflection method to detect the mined area of coal seam,based on the physical parameters of the coal strata in the study area,the geological model of two kinds of goaf in caved and collapsing type is established.Using the tesseral seismic forward software,the seismological records containing different scales of goaf and goaf are simulated.The seismic response,attribute characteristics and recognition ability of the goaf of different types,different scales and different parameters on the horizontal and post stack migration profiles are obtained by means of a series of methods such as cutting initial,pumping,dynamic correction,superposition and migration.The results are compared and analyzed,and the results show that:1.The characteristics of the coalbed goaf on the horizontal stacking time profile are:obvious diffraction,time delay of coal bed reflection,amplitude enhancement,frequency reduction and so on.At the same time,it affects the emission waves in the lower strata,andthe characteristics of the post stack migration profile are: diffraction and convergence,time delay and amplitude increase of coal seam reflection wave.The phenomenon of strong frequency and low frequency lay the foundation for identifying the goaf based on seismic response.2.The simulation shows that the recognition limit of the goaf is λ/2on the horizontal superposition section.The recognition accuracy of the goaf is improved by the post stack migration time after migration treatment.The identification limit of single cavitation goaf is λ/8,and the identification limit of single subsidence goaf is λ/4.The influence range of the goaf on the seismic profile is larger than that in the actual goaf,and the influence range on the post stack migration section is much smaller than that on the horizontal superposition section,which is closer to the size of the actual goaf.It is suggested that the migration section should be used when using seismic reflection to explain the scope of goaf.3.The simulation of the different caving angles of the collapsed goaf shows that the change of the caving angle has a great influence on the recognition accuracy of the collapsed goaf,the greater the caving angle,the higher the recognition precision of the goaf range;in addition,the recognition ability and accuracy of the goaf are controlled by the main frequency of the reflected wave of the coal layer and the recognition ability and the recognition ability The main frequency of the reflected wave in coal seam is proportional to the relationship.4.The response characteristics of two adjacent goaf in post stack migration time vary with the change of two adjacent goaf spacing.The identification limit interval of the adjacent cavern gob in the post stack migration time profile is l,and the limit spacing of the adjacent subsidence gob on the post stack migration time profile is λ/2.In order to further analyze the ability and accuracy of seismic attributes in goaf recognition,the instantaneous amplitude attribute,instantaneous phase attribute and waveform difference attribute of different model sections are extracted and analyzed.1.As a whole,the instantaneous amplitude attribute is more suitable for the goaf recognition and the recognition accuracy is higher;the instantaneous phase attribute and the waveform difference attribute are suitable for the single goaf,and the recognition accuracy is low.2.The identification limit of single cavitation and single collapse goaf in instantaneous amplitude attribute is T,and the identification limit of single cavitation gob in instantaneous phase attribute and waveform difference property is λ/8and λ/4,and the identification limit of single collapse gob in instantaneous phase attribute and waveform difference is λ/4.3.In two adjacent goaf seismic attributes analysis,only the instantaneous amplitude attribute is good for identifying it,and the identification limit is λ/4.It can be seen that the method of seismic attribute is used to explain the goaf,the recognition ability is improved and the recognition accuracy is improved,and the appropriate seismic attributes should be selected to explain the goaf.Based on this,the method of seismic attribute is applied to the interpretation of goaf in research area,and achieved good results.