Dynamic evolution of thermal conductivity of crude oil and formation water under coupled temperature and pressure conditions: A case study of the Chang 7 Member in the Yanchang Formation, Ordos Basin, China

Formation fluid significantly influences the thermal conductivity distribution of rocks under in-situ conversion conditions. Current thermal conductivity measurements are primarily conducted on rocks, or are limited to a single component of crude oil or purified water. In this study, we selected oil and formation water samples of the Yanchang Formation, Ordos Basin to investigate dynamic evolution of thermal conductivity under varying temperature and pressure conditions. An innovative hot-wire method was employed, based on fundamental analysis of fluid physical properties and composition. The results reveal distinct differences in the thermal conductivity between crude oil and formation water. Specifically, the thermal conductivity of crude oil decreases with increasing temperature, whereas that of the formation water first increases and then decreases. This behavior is governed by the density and acoustic velocity of the fluids. Pressure also exerts a significant effect on the thermal conductivity of both the crude oil and formation water, primarily by inducing phase transition and impairing heat transfer. Empirical equation describing the evolution of thermal conductivity under varying temperature and pressure conditions was established, and a corresponding evolution mechanism is proposed. These findings provide valuable references for optimizing temperature and pressure conditions, as well as for the design of mining technologies in in-situ shale conversation systems.