Hiroshi Kiyohashi

Evaluation of the thermal conductivity of granitoid stratum at great depths by core samples

Studies of thermophysical and mechanical properties of rocks at great depths have been conducted as part of research into the hydrology and geochemistry of groundwater, the migration of substances such as uranium, and drift excavation effects on surrounding rock mass by the Japan Nuclear Cycle Development Institute. Measurement results and evaluation are given of thermal conductivity, λ, of core specimens collected from three research wells, 1000 m in depth, dug in granitoid stratum around the Tono mine, Japan. Twenty specimens were collected from each well, taking account of depth interval and lithofacies. The λ value of the specimens was measured by the unsteady hot-wire comparative method in the temperature range 25 - 85 °C. Experimental results showed that the values of λ were 1.9-2.1 W m - 1 K - 1 for conglomeratic sandstone, 2.9-3.6 W m - 1 K - 1 for quartz porphyry, 2.1-3.6 W m - 1 K - 1 for sandstone and 1.9-3.8 W m - 1 K - 1 for granite. A weak reverse temperature dependence of the λ values was observed in the tested temperature range. The distribution of the values of λ versus well depth, Z, showed that the values of λ were influenced by microcracks in the specimens which might have been caused by the stress released during the digging process of the core. In-situ λ values were evaluated with the core data prescribed above and the three-phase geometric-mean model as the A values for the intact rocks eliminated porosity.

Accurate measurement of thermal conductivity of rocks by the transient hot wire comparison method.

An experimental apparatus based on the transient hot wire comparison method was built for measuring the thermal conductivity of both water-saturated and-unsaturated rocks. A new method was developed for determining the time range necessary for calculation of the thermal conductivity in order to measure it accurately. The range is determined by using the second derivative of the hot wire temperature with respect to logarithm of time.The thermal conductivity of water-saturated rocks was measured in a water bath as well as in an airconditioned room. The measurements of the thermal conductivity of water-unsaturated rocks were also made in the same room. The thermal conductivity is able to be measured both in the water bath and in the room within ±5% accuracy in a wide range of 0.05 to 15W/(m·K). For measuring the thermal conductivity of water-saturated rocks, the steady state condition required as initial condition can be easily obtained in a water bath.

Continuous measurement of effective thermal conductivity of well cuttings - water mixture at geothermal conditions by hot-wire method under transient temperature field

Abstract A new continuous technique has been developed for the rapid measurement of the effective thermal conductivity of cuttings-water mixture beds at simulated in situ geothermal conditions to estimate the thermal conductivity of rocks in situ. The technique is based on a modified transient hot-wire method. Beds of mixtures of pure fused quartz grains and water were used as reference samples. Measurements were made at a sample heating rate of 20°C/h from room temperature to 110°C for the reference and to 200°C for the cuttings, and at natural cooling conditions from their maximum temperatures to room temperature. Higher accurate data were obtained with natural cooling than with forced heating. Thermal conductivity of the fused quartz grains estimated from the Kunii-Smith formula and the measured effective thermal conductivity of the sample agreed with literature data within the sum of experimental and estimating errors, ± 15.0% . Data obtained with cuttings from the Satsunan geothermal field, Kyushu, Japan are discussed.

Practical measuring method of thermal conductivity of drilling mud at high temperature and high pressurs.

The transient hot-wire method have been used to measure the thermal conductivity of gases and liquids acculately using a very thin wire of diameter from 15 to 40μm, recently. On the other hand a practical method to measure thermal conductivities of viscous suspensions contained fine and/or coarse grains easily with practically enough accuracies at a high temperature and high pressure is needed in the fields of drilling technology and others. A needle probe type sensor having 2mm in diameter and 1, 000mm in length with a thermopile of six magnifications of sensitivity of temperature and the measuring system were developed. The thermal conductivites of three standard and test samples were measured by analyzing the data of smooth curve relations at an early period between the temperature increase of the probe and the constant heat supplied time to the probe using a theory of unsteady hot thick wire method and the multivariate analysis. Measurement errors of this method were estimated at less than ±10%. Thermal conductivity of montmorillonite-water based muds having concentrations of 3.0, 6.0 and 10.0% were measured at the temperature range from 20 to 180°C. From the measurement characteristic temperature and concentration dependencies on the thermal conductivity of the mud were obtained.