Pore-scale numerical studies on determination of the effective thermal conductivity of the fluid saturated porous media

Abstract

Accurate prediction of the effective thermal conductivity (ETC) of a fluid saturated rock is crucial for fulfilling efficient geo-energy harvest practices. In this paper, the ETCs of a rock with 23% porosity and 2.7 W/m·K thermal conductivity when saturated with various fluids, including water, oil, hydrogen gas, and air, are numerically investigated. Advanced digital rock technique is employed to reconstruct the complex solid-pore structure in the rock, and CFD simulations are performed to assess the ETCs, focusing on the influence of fluid type and heat flux direction. The results show the maximum ETC values of 2.10 W/m·K for water-saturated rocks, in contrast to the minimum values of 1.3 W/m·K for air-saturated samples. When the internal fluid possesses a higher thermal conductivity than air, the ETCs of the fluid-saturated rock display minimal anisotropy, while significant anisotropy is observed in the air filling rock sample. The methodology is validated based on satisfactory agreements between the numerical ETC results and the Geometric Mean model predictions in the water saturated rock case. Due to the fact that the commonly used empirical correlations produce significant deviations when applying to low thermal conductivity fluids, a new ETC model that achieves less than 8% deviation for all studied fluid types is proposed based on the numerical results. This study provides pore-scale insights into fluid flow and thermal conduction behavior within fluid-saturated porous media.