Characterization And Measurement Of Electric Characteristics Of Rock Core Based On MICRO-CT

Digital core research can accurately reconstruct the structural characteristics of actual cores,thereby reflecting the characteristics of formation information,and applying them to actual oil reservoir exploration.The measurement and analysis of core electrical parameters is an important part of the study of digital cores,and it is also the basis of logging disciplines.The electromagnetic intrinsic parameters of the core have strong anisotropy and dispersion characteristics.Therefore,this article first starts with the conductivity anisotropy of the core,and innovatively measures 9 of the equivalent conductivity tensor of the square core at one time.Secondly,starting from the analysis of the equivalent permittivity of the core measured by the experiment,based on the parallel plate capacitance and transmission line theory,the frequency dispersion characteristics of the equivalent permittivity of the digital core is studied in the frequency range of 200MHz-20 GHz,with the help of Due to the high-precision features of Micro-CT,it avoids the cumbersome geometric modeling process during numerical simulation and obtains high-precision digital core 3D reconstruction.Numerical simulation studies when the core voids are filled with single-phase and multi-phase materials.The influencing factors of the equivalent dielectric constant dispersion characteristics,and the analysis of the results are compared with the analysis results of the experimental data;finally,the full text is summarized,and regrets and shortcomings are given.The main content of this paper is composed of the following parts.The first part measures the actual core conductivity tensor component.Firstly,the measurement principle of the experiment is analyzed,and a new measurement method is proposed,which can measure the 9 components of the conductivity tensor at one time,so as to improve the accuracy of core measurement and the efficiency of the experiment.Finally,the square sample core and the plunger core are measured separately,and the experimental data is collected to obtain the conductivity tensor component of the stable square sample core.The second part is the broadband equivalent permittivity measurement study of actual cores.Firstly,the parallel plate capacitance method,the transmission line method and the coaxial probe method for measuring the dielectric constant are studied,and the result is that the coaxial probe method is the most effective method to measure the dielectric constant of the core.Secondly,based on the Keysight N1501 A coaxial reflection method fixture and vector network analyzer,the equivalent permittivity value of the sample core and plunger core under the wide frequency range is measured,and the error is analyzed to obtain a more accurate measurement value.Affected by the polarization time response,when the frequency increases,the polarization effect with a slow response time will be weakened,which affects the value of the dielectric constant.The real part of the relative permittivity of the core decreases with the increase of frequency.When the frequency is greater than 5 GHz,the change trend is accelerated.As the frequency increases,the imaginary part of the relative permittivity first decreases and then increases.The third part is the study of the influence law of the dielectric dispersion characteristics of the two-phase material.Analyze the principle of the change of the dielectric constant of the mixed medium under the broadband,and use the gray image obtained by the Micro-CT scan and the Simpleware software to complete the reconstruction of the digital core.Numerical calculations based on COMSOL are carried out to analyze the factors affecting the dielectric constant of the core under the actual pores and the change law of the equivalent dielectric constant of the core under a wide frequency range.As the relative permittivity and conductivity of the core inclusions increase,the real part of the equivalent permittivity of the core as a whole increases accordingly.The real part of the equivalent permittivity of the core has a tendency to increase when the frequency is greater than 1 MHz,and it begins to decrease when the frequency is greater than 1 GHz.Affected by the polarization effect,it tends to stabilize when the frequency tends to 100 GHz.The fourth part is the study of the influence of seepage law in the core on electrical characteristics.First,the electromagnetic field and the seepage mechanical field are coupled,and the characteristics are studied.Then,based on the COMSOL software,the electromagnetic field,phase field,and laminar flow field are coupled to analyze and summarize the seepage law of two-phase flow in a pore.As a result,as the applied voltage increases,the influence of capillary force is smaller,and the flow velocity near the tube wall in the pore is larger.When the volume fraction of the two phases is changed,it has little effect on the seepage process.It lays a foundation for the study of the electrical characteristics of the digital core 3D model and the interaction between seepage laws.