Development of Thermal Property Measurement Procedure of Cuttings by the Transient Plane Source Technique

To evaluate the physics of seismic fault zones, it is important to know the thermal properties and geothermal structure of the formations around the fault zones. Because core samples are not fully collected in some large depth drillings but only cuttings samples are available, it is necessary to measure thermal properties using cuttings. We experimentally examined a new procedure of measurement and analysis for cuttings using the transient plane source technique (also called Hot Disk method) which can simultaneously measure three thermal properties: thermal conductivity, thermal diffusivity and specific heat.

First, we tested the new procedure of thermal property measurement using cuttings of quartz glass (fused silica) as a standard sample. After that, the rock sample measurement was carried out using seven rock cuttings taken from C0009 borehole drilled during IODP NanTroSEIZE Exp. 319. For examining measured results of cuttings, we also measured the same thermal properties using quartz glass cores and rock cores retrieved from similar depths with the cuttings.

In the quartz glass, an accuracy of <3% was obtained in a water saturated state in comparison between the thermal conductivity values of the cores and the cuttings. In the seven rock cuttings, thermal conductivity measured result of four samples showed very similar values as those of cores with a relative error of 3 - 5%. Measurements for the other three samples, however, underestimated the thermal conductivity by 18 - 30%. Probably, causes of the significant underestimation are that the rock cuttings are dried, and their lower volumetric water content and water saturation degree. In the future, we will conduct further experiments using fresh rock cuttings. Overall, since there was sufficient accuracy for the quartz glass and a part of rock cuttings, our experimental results preliminarily suggested that our new proposed procedure might be useful for thermal property measurements of rock cuttings.