To exactly evaluate thermal conductivity of a rock specimen taken from a great depth, pressure effects have to be taken into consideration. We developed a new measurement system of thermal conductivity of rock specimens under high confining pressure and high pore-fluid pressure. This system consists of a commercial thermal conductivity meter, a high pressure vessel in which the rock specimen, sensors of thermal conductivity measurements were installed and two high resolution syringe pumps. One of the syringe pumps is for controlling confining pressure; and the other is for pore-fluid pressure. Both the pumps are able to monitor fluid flow rate and cumulative volume change of pore fluid in rock specimen assembly during testing. We examined the effects of high pressure on thermal conductivity in rock specimens of five terrestrial rock types. Thermal conductivity clearly increased with increasing effective pressure for both dry and wet (water saturated) samples.
In case of the geological disposal of high-level radioactive waste at a large depth in underground, thermal conductivity of rocks under in-situ pressure and temperature conditions is the most important key parameter for estimations of temperature increasing of the rocks around the canisters associated to generation of heat by radioactive materials. The physical properties of rocks, including thermal conductivity, are dependent on pressure and temperature (Schön 1998), so in situ pressure and temperature conditions should be simulated in laboratory measurements of the thermal conductivity of drill core samples from great depths.
General, thermal conductivity of rock samples are measured at atmospheric pressure condition in civil and geotechnical engineering fields. Several previous studies on thermal conductivity at high confining pressure were found in mining and geoscience fields (e.g. Horai and Susaki 1989; Abdulagatova et al. 2009), but almost of them did not take pore-fluid pressure into consideration. We developed a new apparatus capable of measuring the thermal conductivity of a rock sample at both high confining pressure and high pore-fluid pressure conditions based on our previous system which was able to measure the thermal conductivity under high confining pressure condition only (Lin et al. 2011).