Acoustic Properties Research Of Coal With Digital Cores

Rock physics is a bridge between reservoir geological characteristics and seismic response characteristics.It is the basis of reservoir prediction and plays an important role in geophysical research.Traditionally,rock physics research is based on physical experiments.However,due to the limitations of rock samples and testing methods,traditional Rock physical research methods cannot fully meet the needs of actual production.With the development of computer technology and the application of X-ray CT scanning technology in Rock physics experiment,digital Rock physics technology provides a new technical means for Rock physics research.In this study,the acoustic characteristics of coal rocks in the carboniferous No.10 coal seam of Luling coal mine in Huaibei coalfield were systematically studied with digital Rock physical technology as the main means,and combined with the traditional Rock physical experimental testing technology,and the reliability of the study on the acoustic characteristics of coal rocks based on digital Rock physical simulation testing technology was verified.For the testing and research of the acoustic characteristics of coal and rock,the longitudinal and transverse wave velocity tests and velocity anisotropy tests were carried out on 12 coal samples under laboratory conditions by means of ultrasonic testing equipment.First of all,the vertical and horizontal wave velocity test of the coal sample was completed,and the parameters such as the vertical and horizontal wave velocity,the vertical and horizontal wave velocity ratio,the dynamic Poisson ratio and the dynamic elastic modulus of the coal sample were obtained under the conditions of different axial pressures and confining pressures.Secondly,the velocity anisotropy test of the coal sample was completed,and the longitudinal and transverse wave velocities of the six directions were obtained,and the relationship between the longitudinal and transverse wave velocities and the pseudo-azimuth was obtained.Finally,industrial analysis,elemental analysis,component identification and true density test of coal samples are carried out for different types of structural coal,and the corresponding relationship between velocity anisotropy and physical properties of coal samples is analyzed and studied.It is found that the chemical components of different coal samples have good correlation with their velocity anisotropy.For the study of digital core construction of coal and rock,the 12 coal samples collected in this study are taken as the research object.First,the actual coal samples were imaged by X-ray CT scanning.The CT images of coal samples with high quality were obtained by scanning 37.8 micron and 7.32 micron respectively.Secondly,combined with the existing digital image processing methods and software,the image preprocessing,image segmentation and post-processing of CT scan images of coal samples are studied to study the processing algorithm and process flow suitable for CT images of coal samples,highlighting the image differences between coal rock microstructure and mineral components.Finally,the image reconstruction algorithm is used to construct the 3d digital core of coal rock on the basis of the processed 2d images of coal samples.For the acoustic characteristics simulation research of coal rock,based on the basic theory of three-dimensional digital core and elastic mechanics,the finite element algorithm is used to carry out the microscopic acoustic simulation research.In the simulation,the digital core is firstly imported into the finite element simulation software to form the structural model.Secondly,the structure mechanics constitutive relation and fixed constraint boundary condition are used to construct the simulation model.The acoustic response of rock samples is simulated by giving corresponding elastic modulus to each structural unit.By comparing the simulation results with the experimental results,it is found that there is a high consistency between the two,which verifies the effectiveness of the proposed simulation method.The influence of microstructure and components of coal and rock on velocity anisotropy is studied by means of simulation and experimental test of velocity anisotropy of digital core of coal sample.In summary,this paper studies the acoustic characteristics of coal rock comprehensively by combining the digital core simulation test technology with the traditional rock physical experiment test technology.It not only reveals the acoustic velocity and velocity anisotropy of coal and rock,but also makes clear the main factors that influence the acoustic characteristics of coal and rock.