Thermal properties of rock core samples and their correlations with other physical properties in the volcanic region surrounding the Aso Volcano

• Proposed a thermal conductivity–porosity model specific to saturated volcanic rocks. • Identified a thermal conductivity–P wave velocity relation for alternative estimation. • Validated the geometric mean model as optimal for volcanic rock thermal conductivity. • Provided an extensive dataset for modelling thermal properties in volcanic regions. Understanding the thermal properties of underground geological formations is crucial for geothermal energy exploration and subsurface modelling. However, data from typical volcanic regions, such as the Aso volcanic region in Japan, remain limited. This study addresses this gap by providing comprehensive measurements of thermal properties, porosity, bulk density, and elastic wave velocities of rock core samples obtained from a scientific drilling project in the Aso volcanic region. The findings reveal that thermal conductivity is significantly higher under saturated conditions than under dried conditions, underscoring the critical influence of water content on subsurface thermal behaviour. An inverse relationship between thermal conductivity and porosity was observed, with a more gradual decrease under saturated conditions due to the thermal conductivity of pore-filling fluids. Through detailed analysis, this study identifies reliable methods for estimating thermal conductivity based on porosity and compression wave velocity, particularly suited for volcanic rocks. These approaches offer practical alternatives when direct measurements, which require intact rock core samples, are not feasible. They provide satisfactory accuracy for preliminary predictions prior to conducting detailed investigations. Additionally, the evaluation of mixing models demonstrated that the geometric mean model effectively captures the influence of pore structure and mineral composition on bulk thermal conductivity, providing a reliable framework for understanding heat transfer processes in volcanic subsurface regions. By contributing valuable thermal property data and advancing predictive methodologies, this work enhances geothermal modelling and resource assessments, serving as a reference for similar volcanic regions worldwide.