| The study of the effective electrical properties of reservoir rocks can be used to determine the distribution of underground oil and gas storage and to identify the oil and water layers.The accurate evaluation for the effective electrical properties of rock models by digital means is of great significance for not only the theoretical rock physics,but the development of experimental methods,and the application of electrical logging methods.As a new core analysis method,digital rock core technology has gradually become one of the effective methods to study the effective electrical properties of rock.Based on the technology of digital core and electromagnetic simulation,the data processing for sample image dataset,the numerical 3D rock model transformation and the computation of the effective electrical properties are carried out systematically.Furthermore,six types of rock sample such as sandstone and shale are investigated to discuss the validity and accuracy of the numerical core analysis method by comparing with the experimental results.First,based on the CT tomography image of rock samples,the type of noise generated by analyzing the imaging principle of CT scanning is analyzed and the image preprocessing is carried out.In order to determine their best segmentation thresholds,according to the distribution patterns of two gray scale histograms of the normal distribution and bimodal distribution,different methods of image segmentation are proposed respectively,and the porosity of rock samples is calculated accordingly.Second,on the basis of digital rock core image data,we build a three-dimensional numerical model of rock.According to the characteristics of electromagnetic simulation software which based on finite element algorithm,we designed and implemented a method of efficiently converting core two value image data to 3D numerical model.Finally,using the script file control method,the HFSS electromagnetic numerical simulation software is used for meshing the core model and calculating and analyzing of the effective electrical properties.Comparing the experimental measurement results with the core numerical analysis calculation results,the results of effective electrical properties by two methods fit well.The validity and accuracy of the numerical core analysis method implemented has been verified further.This set of methods for data processing,numerical model conversion and calculation of electromagnetic parameters for scanned core images can be used for efficient and accurate analysis of different types of digital core dielectric constant,conductivity and other properties,which can provide important reference for the rock physics,logging interpretation and reservoir evaluation etc. |
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