Development of Methods and Instruments for Thermal Conductivity Measurements of Standard Rock Samples for Petrophysical Studies

The article presents the problem of low reliability and accuracy during the determination of the thermal conductivity of small-sized rock samples using existing measuring instruments. A laboratory unit was developed for measuring the thermal conductivity of standard rock samples used for petrophysical studies with a diameter of no more than 30 mm. The unit was tested on small-sized samples. The laboratory unit was analyzed to find and understand any potential issues related to its design, manufacture, or operation. An algorithm was created for the automated collection and processing of qualitative data. The key factors likely to be detrimental to the accuracy and reliability of the measurements were identified and addressed. These include unshielded thermocouples, unwanted changes in potential between the hot and cold junctions of the thermocouple due to the uneven melting of the water–ice mixture in a Dewar vessel, suboptimally designed shape and dimensions of the object of study, and the nonequilibrium ratio of the input and output thermal energy. The unit was calibrated on reference samples of pure tin and LS59 brass with known values of thermal conductivity. The thermal conductivity of a rock sample with a height of 4.28 mm and a diameter of 30 mm was determined with an error of no more than ±5.6%. This study can be a guide for assessing the thermal conductivity of small rock samples in the range of 0.3–70.0 W/(m·K) in the temperature range of 20°C–60°C.