| Influenced by the in-situ stress in different directions and the regular arrangement of cracks,the rock has different acoustic characteristics in different directions,which is called acoustic anisotropy of rock.The anisotropy of rock is very important for stratigraphic evaluation and oil and gas exploration.How to obtain rock anisotropy more accurately has always been an important topic in geophysical circles.In addition,studying the anisotropic properties of rock samples is important for the exploration and development of unconventional oil and gas resources.In this paper,the acoustic characteristics of anisotropic rock samples are studied by theoretical numerical simulation and experiments.The anisotropy properties of rock samples are obtained by measuring the longitudinal and transverse wave velocities of anisotropic rock samples.A method for measuring the acoustic characteristics of spherical rocks in all directions is proposed,which provides a new idea for the evaluation of anisotropy.The first part combines the elastic wave theory with numerical methods to study the acoustic properties of anisotropic rock samples.The acoustic properties of isotropic background media filled with fluid fissures were studied by finite element method.The effects of fissures on the acoustic properties of rock samples were studied by changing the aspect ratio,rotation angle and fracture density of the fractures.Then the lateral isotropic two-dimensional simplified model is simulated,and the relationship between the waveforms in different azimuths and the angle of the acoustic propagation path is obtained,and the variation of the sound velocity and the receiving amplitude with the number,angle and aspect ratio of the cracks is made.Quantitative analysis.The second part uses the omnidirectional acoustic measurement system of the laboratory to measure two spherical rock samples with different bedding structures but different lithologies.The waveforms of the longitudinal and transverse waves under various orientations of the rock samples are obtained,and the time is extracted from the waveform.The longitudinal and transverse wave velocities of the rock samples are calculated.The results show that the wave velocity first increases with the increase of the measurement angle,and takes the maximum value around 90°.Then,as the measurement angle increases,the minimum value is taken near180°.The anisotropy of the rock samples in all directions is thus obtained.On this basis,the measured longitudinal and shear wave velocities are analyzed,and the relationship between longitudinal and shear wave velocities is obtained.The elastic and mechanical parameters of different directions of rock samples are analyzed by combining longitudinal and shear wave velocities,and the mechanical parameters are measured.The relationship of angles.The experimental results were normalized and compared with the previous simulation results.It was found that the experimental results and the simulation results were basically consistent,and the validity of the results was verified. |
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