Thermal conductivity models of sandstone: applicability evaluation and a newly proposed model

The thermal conductivity (TC) of rock has a general application in safety assessment and engineering optimization of deep geological engineering practices such as geothermal mining and nuclear waste disposal. Determining the TC of rock by using a TC model is a convenient and effective method for such evaluation, and selecting a suitable TC model is key for ensuring accurate calculation results. In this study, we firstly select eight two-phase TC models to evaluate the applicability to sandstone. Secondly, the TC values of sandstones in various porous media such as air, water, and ice are measured by using the transient plane source (TPS) method, and the mineral composition and content were determined by using X-ray diffraction (XRD) and the Cross, Iddings, Pirsson, and Washington (CIPW) norm. Thirdly, the TC values of sandstones in different porous media are also calculated by using the eight models, and their deviations are analyzed to compare their applicability. Finally, by considering of the influence of pore structure on the rock TC, a new TC model referred to as the thermal resistance–connectivity (TRC) model is proposed for sandstone based on pore connectivity, and the mean deviation is compared with the previous model. Several results are obtained. Among the eight common models, the geometric mean model is found to be more accurate than other models regardless of all three states. In particular, for the porous medium filled with ice, the calculated value of the Geometric mean model had the most significant agreement with the measured value. In addition, the mean deviation of the TRC model for all three states is shown to be more consistent with the measured value than the eight models. Therefore, we recommended the TRC model for calculating the TC of sandstone. This study provides a novel method for determining the TC value for deep geological assessment.