Temperature effect on thermal-diffusivity and heat-capacity and derived values of thermal-conductivity of reservoir rock materials

Abstract

A laser flash method (micro-flash apparatus LFA 457) and differential scanning calorimeter (DSC 204 F1) were employed to study of the temperature effect on the thermophysical properties (thermal diffusivity $a$, heat capacity $C_{\text{P}}$ and thermal conductivity $\lambda$) of the natural reservoir rock sample. A relationship between the thermophysical properties behavior and the physical–chemical processes (thermal decomposition of pore heavy oil and volatilization of pore fluids) occurring in the rock’s pore fluids during heating in distinct temperature ranges was established. The measurements of the thermal-diffusivity have been made over the temperature range from 295 to 774 K. The isobaric heat capacities (C_P) of the same sample were measured in the temperature range from 308 to 768 K. Uncertainties of the measurements are 3% and 1% for $a$ and $C_{\text{P}}$, respectively. The significant effect of thermal decomposition on the measured values of heat-capacity of reservoir rock sample at high temperatures (above 680 K) was experimentally found. We experimentally observed temperature anomaly of the heat capacity of rock sample in distinct temperature ranges, around 380 K (low-temperature range) and 680 K (high-temperature range).We attribute these anomalies to the dehydration (evolution of the volatile matter, VM, devolatilization) and aromatization of the carbon (thermal decomposition), which are known to occur under heat treatment. This leads to unusual increasing the heat capacity at high temperatures. Measured values of thermal diffusivity ($a$) and heat capacity ($C_{\text{P}}$) together with density data ($\rho = { 2210}\;{\text{kg}}\;{\text{m}}^{ - 3}$) were used to calculate the derived key properties, thermal conductivities ($\lambda$) of the rock sample, using very well-known relation, $\lambda = a\rho C_{\text{P}}$.