Seismic Wave Finite Difference Modeling Of Coalfield Limestone And Analysis On Response Characteristics

Coal mine water disaster always existed side by side with coal production,causing severe effect on coal safety production.The aquifer of the coal seam floor mainly consists of Carboniferous and Ordovician limestone and etc.,among which the water-abundance of Ordovician limestone is better.Based on the basic theory of rock physics,this thesis established the rock physics model of saturated limestone and variable porosity saturated rock to carry on elastic wave finite difference forward simulation.Thus we conducted an analysis on the seismic response characteristics of water-saturated and variable porosity saturated limestone.The finite difference(FD)method has been widely applied to the numerical seismic elastic wave simulations,among which FD coefficients determine the precision of numerical simulation.In this thesis,the FD coefficients were captured by fruit fly optimization algorithm(FOA),which minimized the absolute error of the space-domain dispersion relation of acoustic equation.Compared with Taylor series expansion method(TEM),the results showed that FOA-based method had better capability to suppress the numerical dispersion.Meanwhile,based on the recursive integral perfectly matched layer absorption(RIPML)method,this thesis extended the FOA to the first order velocity-stress equation for coalfield limestone numerical modeling.The single-axis and tri-axial stress loading tests on limestone were conducted through ultrasonic P?S wave integrated tester for accurate P-wave and S-wave velocities measurement of rock sample at room temperature.The self-consistent approximation model was adopted to calculate the modulus of saturated and saturated variable porosity limestone.Then the initial model of coalfield limestone and the rock physics models of saturated and saturated variable porosity were built.By carrying out the seismic wave FD forward modeling and horizontal superposition,the seismic wave characteristics of the limestone initial saturated model and saturated models with porosity of 5%,8% and 10% were analyzed and made a comparison.The modeling results indicated that the reflected wave formed by the rhythm type of thin interbedding of coalfield limestone and sand shale was a composite wave,and the larger the impedance difference between the coalfield limestone and the sand shale surrounding rock,the greater the amplitude of the seismic amplitude response,on the contrary,the amplitude would be smaller.Due to the complex geology structure of the ground stratum,it is necessary to have a further analysis on the response characteristics of the limestone rock physics model.