Heat Transfer in Sandstones at Low Temperature

This paper addresses experimental and modeling investigations of heat transfer in sandstones subject to low-temperature conditions. At low temperature, pore liquid (e.g., water) would freeze; thus, heat is transferred not only in the form of specific heat but also in the form of latent heat. Moreover, the melting point is not constant; it depends on the pore size. Considering these characteristics, a governing equation of heat transfer with phase transition is established using the equivalent heat-capacity method. To calculate the equivalent heat capacity, the relation between ice content and temperature is assessed by the pore-size distribution curve. Heating tests (from 77 to 293 K) of sandstone samples in three saturation conditions (water-saturated, oil-saturated, and dry) are conducted and simulated using the model established. The results reveal that the temperature sensitivity of the heat capacity of dry sandstone is more pronounced in the low-temperature regime than in the high-temperature regime. The thermal conductivity of dry sandstone increases with temperature in the low-temperature regime. This is different with the case of the high-temperature regime at which the thermal conductivity decreases with temperature. The temperature evolution curve for the water-saturated sample features a plateau regime, that is, the temperature remains quasi-constant with time. The analysis demonstrates that the position and length of this temperature plateau are governed by the pore-size distribution.