Measurements of Thermal Conductivity of Intact Rocks by Using Cuttings

Abstract

Generally, mixing models are necessary in case of estimating thermal conductivity of an intact rock from thermal conductivity of cuttings of the same rock. However, one of the problems about this is difficulty in determining suitable mixing model. To develop a simple method to determine thermal conductivity of an intact rock by thermal conductivity measured using cuttings of the rock without any mixing model, we experimentally examined relationship between thermal conductivities of rock cuttings and core samples. We used totally 15 typical rock samples and two fused silicas, including five sedimentary rocks, nine igneous rocks, one metamorphic rock, and made two categories of cuttings size distribution as ≥2 & <4 mm and <2 mm. Then, we measured thermal conductivity of water-saturated intact rock core λ_core and thermal conductivity of mixture of cuttings and water λ_probe by hot disk method and using a new measurement probe for cuttings, and also investigated relationship between two values. As a result, we found a satisfactory linear correlation and got an empirical equation between λ_core and λ_probe as λ_core=4.65λ_probe−2.38 (0.8 < λ_probe < 1.5 Wm^-1K^-1) for ≥2 & <4 mm cuttings and average relative error (RE_ave) of thermal conductivity estimation based on this equation was 6.4%. In comparison between the two categories of size distribution of cuttings, RE_ave of ≥2 & <4 mm cuttings was smaller than that of <2 mm cuttings and we concluded ≥2 & <4 mm cuttings was suitable for this method. In addition, estimation by our empirical equation was more accurate than those of previous mixing models, probably this is owing to less factors of our empirical equation which effect on the estimation. Finally, we proposed this new measurement method to determine thermal conductivity of intact rock using thermal conductivity of cuttings based on this new empirical equation without using any mixing model.