Experimental setup for measuring thermal conductivity of rocks under water-saturated conditions at increasing temperatures using the Transient Plane-Source technique

<title>Abstract</title> <p>Accurately measuring the thermal conductivity of rocks under in situ subsurface conditions is crucial for heat-flow and resource assessment in geological reservoirs such as geothermal aquifers. Besides mineralogy and texture, rock thermal conductivity is a function of numerous variables such as pressure, temperature and saturation. However, thermal measurements are often taken on dry specimens under ambient lab conditions, so are unrepresentative of subsurface reservoirs. This study introduces a novel experimental set-up using the Transient Plane Source (TPS) method to address this gap. Using sandstone samples from the Permo-Triassic Sherwood Sandstone Chester Formation, a geothermal prospect in the Cheshire Basin (UK), thermal conductivity was measured under water-saturated conditions at temperatures of 30°C, 50°C, 70°C, and 90°C. These direct measurements obviate the need to use mathematical mixing models to adjust dry-state data for saturated conditions. Two different configurations were tested, and results indicate a relatively high thermal conductivity due to water saturation, and a temperature-dependent decrease in thermal conductivity in both cases. Some inconsistencies in outcrop samples were noted, likely stemming from experimental setup challenges. The study suggests improvements for the experimental setup, including the use of a circulating water bath with a transparent lid, appropriate clamping mechanism, and ensuring flat sample surfaces. This new measurement technique enhances the understanding of thermal properties under realistic reservoir conditions.</p>