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 a suitable mixing model. To develop a simple method to determine the thermal conductivity of an intact rock by thermal conductivity measured using cuttings of the rock without any mixing model, we experimentally examined the relationship between the 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: ≥2 and <4 mm and <2 mm. We then measured thermal conductivity of the water-saturated intact rock core λcore and the thermal conductivity of a mixture of cuttings and water λprobe by the hot disk method and using a new measurement probe for cuttings, and also investigated the relationship between the two values. As a result, we found a satisfactory linear correlation and got an empirical equation between λcore and λprobe as λcore = 4.65 λprobe − 2.38 (0.8 < λprobe < 1.5 Wm-1K-1) for ≥2 and <4 mm cuttings and the average relative error (REave) of the thermal conductivity estimation based on this equation was 6.4%. In comparison between the two categories of size distributions of cuttings, the REave of ≥2 and <4 mm cuttings was smaller than that of <2 mm cuttings, and we concluded that ≥2 and <4 mm cuttings are 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 the thermal conductivity of intact rock using thermal conductivity of cuttings based on this new empirical equation without using a mixing model.
Hashimoto et al. (Thu,) studied this question.