The Tomography Method Of The Transmitted Waves In Coal Mining Face

Coal is the main resource of China and the basis of the national economic development.Coal resource is very rich in China which distributes widely.Occurrence of coal seam has poor geographical span,complicated geologic structure and many geological factors causing disasters.Therefore,to ensure the safe and efficient production of coal mines,it is urgent to find the geological anomalies in the coal mining face more precisely.Due to its high detection accuracy,the transmission seismic exploration technology of coal mining face has gradually become the premier choice for obtaining geological conditions of the coal mining face accurately.Several seismic waves with different properties will be generated when the seismic waves are excited in the coal mining face.The most prominent wavefield characteristics are the refracted waves with first reaching the receivers that propagate along the surrounding rock and channel waves with the strongest energy that propagate in the coal seam.First of all,the propagation law of the transmitted waves is studied.Transmitted body waves and channel waves are separated using sparse hyperbolic Radon transform in frequency domain.Meanwhile,based on compressed sensing,the research with the reconstruction of the transmitted waves field is carried out,and the characteristics of the Airy phase are highlighted by the generalized S-transform.Finally,to take advantage of the refracted waves and the transmitted channel waves,a multidirectional anisotropic total variation regularization is proposed to tomography the surrounding rock of coal mining face and an improved total variation is applied to study the attenuation coefficient tomography of the transmitted channel waves.The aim of the research is to better understand the transmitted waves of coal mining face,so as to further improve the imaging accuracy of coal mine face which meets the requirements for safe and efficient mining production.The simulation of transmitted wavefield is an important way to understand the propagation law of the transmitted waves.Most of the existing wavefield simulation methods are based on finite differences,and the calculation accuracy needs to be further improved.Moreover,the finite difference method is more complicated to deal with the boundary conditions of air tunnel.This thesis performs the simulation of transmitted waves in coal mining face using ANSYS platform and APDL(ANSYS Parametric Design Language).The results show that the propagation law of the transmitted waves is correct and reliable.The refracted waves propagating along the surrounding rock reach the receivers first,and the channel waves propagating in the coal seam arrive last,which have the characteristics of long wave train,strong energy and high frequency.Due to the different properties of transmitted body waves and transmitted channel waves,the imaging methods are also different.In this thesis,a sparse hyperbolic Radon transform with high resolution in frequency domain,which is better than the time domain Radon transform,is proposed to separate transmitted body waves and transmitted channel waves.In the process of data collection,empty or bad traces are inevitable.This thesis proposes a sparse hyperbolic Radon transform with high resolution in frequency domain based on compressed sensing to reconstruct transmitted waves.The results show that it can get better reconstruction when the missing data is symmetrical about the vertex of hyperbola.The rationality of the Airy phase identification from the transmitted channel waves is closely related to the accuracy of the tomography.Nowadays,S-transform is widely used in the analysis of dispersion curve,however,its application is limited with the fixed window.In order to improve the identification accuracy of the Airy phase of the dispersion curve,the generalized S-transform with adjustable window is introduced into the analysis of dispersion curve.The window of generalized S-transform is analyzed by temporal full width at half maximum(temporal FWHM).It can be concluded that,for a frequency range,a narrower window indicates a higher temporal resolution and a lower frequency resolution and vice versa.The time-frequency resolution can be adjusted quantitatively according to the relationship between the temporal FWHM and the parameters of generalized S-transform in application.The synthetic and real data results show that the generalized S-transform can effectively improve the time-frequency resolution and the Airy phase characteristics of the dispersion curve.It is helpful for the interpreter to pick up the Airy phase of the transmitted channel waves accurately.The computed tomography(CT)reconstruction algorithm is one of the crucial components of the CT system.To date,total variation(TV)has been widely used in CT reconstruction algorithms.Although TV utilizes the a priori information of the longitudinal and lateral gradient sparsity of an image,it introduces some staircase artifacts.To overcome the current limitations of TV and improve imaging quality,we propose a multidirectional anisotropic total variation(MATV)that uses multidirectional gradient information.The surrounding rock of coal mining faces uses principles of tomography similar to those of medical X-rays.The velocity distribution of the surrounding rock can be obtained by the first-arrival traveltime tomography of the transmitted waves in the coal mining face.And combined with the geological data,we can interpret the geological hazards in the coal mining face.To perform traveltime tomography,we first established the objective function of the first-arrival traveltime tomography of the transmitted waves based on the MATV regularization and then used the split Bregman method to solve the objective function.The simulated data and real data show that the MATV regularization method proposed in this thesis can better maintain the boundaries of geological anomalies and reduce the artifacts compared with the isotropic TV regularization method and the anisotropic TV regularization method.Furthermore,this approach can more accurately and effectively describe the distribution of geological anomalies and improve imaging accuracy.Transmitted channel waves provide a lot of information about coal seams.Many existing studies have picked up the traveltime of Airy phase trace by trace,and then carry out traveltime tomography.Because of the large number of transmitted channel waves and the accuracy of the Airy phase traveltime,it is necessary to find a tomography method which is more efficient and accurate.Based on the the three dimensional forward modeling of rock-coal-rock with several types of geological anomalies,this thesis proposes a tomography method with attenuation coefficient of the transmitted channel waves using improved total variational regularization.Several numerical models are used to verify the proposed method.For the collapse column model and the coal seam thinning model,the results of the proposed method have high quality in x-,y-,and z-component at high frequency band.For the the model with the fault throw of 2m,the results of the proposed method have high quality in x-component at high frequency band.The real data example shows that the proposed method can better match the actual geological anomalies that are revealed and can better describe the distribution range of the geological anomalies.