Digital core models reconstructed using X-ray tomography (X-CT) enable the quantitative characterization of the pore structure in three dimensions (3D) and the numerical simulation of petrophysics. When the X-CT images accurately reflect the micro structures of core samples, the greyscale threshold in the image segmentation determines the accuracy of digital cores and the simulated petrophysical properties. Therefore, it is vital to investigate the comparison parameter for determining the key greyscale threshold and the criterion to describe the accuracy of the segmentation. Representative coquina digital core models from X-CT are used in this work to study the impact of grayscale threshold on the porosity, pore percolation, connectivity and electrical resistivity of the pore scale model and these simulations are calculated by Minkowski functions, component labeling and finite element method, respectively, to quantify the pore structure and simulate electrical resistivity. Results showed that the simulated physical properties of the digital cores, varied with the gradual increase of the greyscale threshold. Among the four parameters related to the threshold, the porosity was most sensitive and chose as the comparison parameter to judge the accuracy of the greyscale threshold. The variations of the threshold change the micro pore structures, and then the electrical resistivity. When the porosity of the digital core model is close to the experimental porosity, the simulated porosity exponent matches the experimental porosity exponents well. The good agreement proved that the porosity is the critical comparison parameter to describe the accuracy of image segmentation. The criterion is that the porosity of the digital core after segmentation should be close to the experimental porosity.

使用X射线断层扫描（X-CT）重建的数字岩心模型可以在三个维度（3D）上对孔隙结构进行定量表征，并进行岩石物理学数值模拟。当X-CT图像准确反映岩心样品的微观结构时，图像分割中的灰度阈值确定了数字岩心的精度和模拟的岩石物理特性。因此，研究确定关键灰度阈值的比较参数和描述分割精度的标准至关重要。使用X-CT的代表性Coquina数字核心模型来研究灰度阈值对孔隙度模型的孔隙率，孔隙渗透，连通性和电阻率的影响，并且这些模拟是通过Minkowski函数计算的，分别用组分标记法和有限元法定量孔结构并模拟电阻率。结果表明，数字核的模拟物理特性随灰度阈值的逐渐增加而变化。在与阈值相关的四个参数中，孔隙率最敏感，因此选择它作为比较参数来判断灰度阈值的准确性。阈值的变化会改变微孔结构，然后改变电阻率。当数字岩心模型的孔隙度接近实验孔隙度时，模拟孔隙度指数与实验孔隙度指数非常吻合。良好的协议证明，孔隙率是描述图像分割精度的关键比较参数。