Geothermal measurements

Geothermal measurements give information on the thermal properties of rocks, such as temperature gradient and heat flow density.

The properties measured in the laboratory are thermal conductivity (ability to conduct heat), specific heat capacity (ability to store heat) and thermal diffusivity (rate of heat transfer). Thermal diffusivity is calculated from the thermal conductivity divided by density times specific heat capacity.

In the divided bar method, geothermal measurements are made on 7 mm thick (drill core) samples. Before measurements, the samples are saturated with water at room temperature and pressure.

Another device in the laboratory to measure geothermal properties is the Hot Disk Thermal Constant Analyser, which uses the transient plane source (TPS) method. Measurements can be made as a function of temperature (maximum 180°) and by taking into account the texture of the rock.

Measurements can be made either on drill cores (preferred) or on hand samples. The sample is typically split into two pieces, so that the sensor can be inserted between the two halves.