Thermal Petrophysics Lab

The lab is a facility maintained by research cluster ‘Temperature field of the Earth’ of section 6.2. The lab produces data that are part of projects related to the analysis of the Earth temperature field. Thermal conductivity and thermal diffusivity of dry and saturated rocks are measured under ambient laboratory conditions using the optical scanning technology, needle probe and half space line source methods.

Devices available :

  • Thermal conductivity scanner (TCS)
  • TK04

A laboratory device is in the making allowing for dry and saturated rocks measurements at pressures and temperatures that are simultaneously raised to 250 MPa and 250 °C, respectively. The device that uses a modified pulse method. For an extended analysis of high-temperature thermal properties, we collaborate with partner laboratories. This pertains to:

  • Laser-flash analysis (up to 1200 K)
  • Differential calorimeter (up to 1200 K)
  • Transient plane source techniques (up to 1200 K)

The best raw material for analysis is full core, but thermal properties can be also measured from half core or cutting samples. For the preparation of samples the GFZ facilities are employed.

We have extensive lab experience with all types of rocks (sedimentary rocks, magmatic and metamorphic rocks). Saturation of rocks is accommodated with varying fluids (air, tap water, distilled water, heptane, etc.). We also provide service measurements. For information on sample analysis and conditions and processes contact us by email.

The Thermal Conductivity Scanner (TCS) is a contactless (non-destructive), continuous, and very fast device to measure profiles of thermal conductivity and/or thermal diffusivity with a spatial resolution of 1 to 3 mm with a high accuracy and precision: < 3% (TC mode) and < 5% (TC,TD mode) (Popov et al., 1999; Popov et al., 2003). The samples surface required has no strict requirements to the shape and dimension but best results are achieved with a plain surfaces. Stripes of acrylic varnish 10-15 mm wide and 30 µm thick have to be painted as an optical coating that unifies the optical reflection coefficients of the rock components.

The "Optical Scanning" technique was introduced by Yuri Popov (Popov, 1983; Popov et al., 1984). Figure 1 shows the apparatus and the principle of operation (Popov et al., 1999), which is based on scanning a sample surface with a focused, mobile, and continuously operated constant heat source in combination with a temperature sensor. The heat source and the sensor move with the same speed relative to the sample and at a constant distance to each other. From the maximum temperature rise, the source power and the distance between source and sensor, thermal conductivity can be calculated. The measured sample(s) and reference standards with known thermal properties are aligned along the scanning direction.

This method excels in its ease in use, which is high speed in operation, noncontact mode of measurement, and the ability to measure directly on a core or plain outcrop sample showing the heterogeneity of the rock sample along the scanning line.

References

  • Popov, Y. A. (1983). "Theoretical models of the method of determination of the thermal properties of rocks on the basis of movable sources: Part 1 (in Russian)." Geologiya i Razvedka "Geology and Prospecting"(9): 97-103.
  • Popov, Y. A., V. G. Semionov, V. M. Korosteliov and V. V. Berezin (1984). "Non-contact evaluation of thermal conductivity of rocks with the aid of a mobile heat source (in Russian)." Izvestiya, Physics of the Solid Earth 19(563-567): 83-86.
  • Popov, Y. A., D. F. C. Pribnow, J. H. Sass, C. F. Williams and H. Burkhardt (1999). "Characterization of rock thermal conductivity by high-resolution optical scanning." Geothermics 28(2): 253–276.
  • Popov, Y., V. Tertychnyi, R. Romushkevich, D. Korobkov and J. Pohl (2003). "Interrelations between thermal conductivity and other physical properties of rocks: Experimental data." Pure and Applied Geophysics 160(5–6): 1137–1161.

For the determination of thermal conductivity at ambient conditions a commercial needle-probe apparatus (TK04, Fa. TeKa Berlin) is used as well. The measurement principle is based on the transient heat flow technique: a cylindrical heat source is constantly heated and the increase of temperature is registered inside the source. The temporal evolution of the heating curve is used in order to calculate the thermal conductivity of the sample material. Typically about 80 seconds are required for one single measurement. Multiple measurements under identical conditions can therefore be performed within short periods of time.

Using standard methods, the result of the evaluation depends on the choice of an undisturbed evaluation interval. Within practice, using a fixed evaluation interval is not useful, because the position depends on many different parameters like thermal conductivity and diffusivity, as well as the size of the probe, contact resistance, etc. Therefore for this apparatus a special approximation method (SAM) was developed. The entire heating curve is evaluated within up to 3000 different time intervals. For every interval the suitability for the determination of thermal conductivity is tested on the basis of mathematical and physical criteria. From the results of all physically meaningful solutions, SAM automatically chooses the optimal, i.e. least disturbed, time interval and the resulting thermal conductivity value. Both the measurement data (temperature versus time) and the evaluation results are stored for every measurement and can be used for subsequent analysis. A special graphics package can be employed to visualize the results of specific measurements and to display additional data in order to evaluate the overall measurement quality. Because the scatter of the results is an indicator for external influences and/or inappropriate measurement settings (heating power, evaluation parameters), the results of a series of measurements can be reviewed and disturbing effects can be traced more easily.

Two different types of probes are available:

  • Full-space line source (VLQ): The "needle probe" is comprised of a steel tubule with an integrated heat element and a temperature sensor. The VLQ is suited for all materials in which a small hole can be drilled in order to insert the probe, as well as powdered materials and viscous fluids.
  • Half-space line source (HLQ): The heat source is designed like the VLQ and is embedded inside the bottom of a cylindrical block with known thermal properties. The HLQ is suited for all samples with smooth surfaces and for measurements on mixtures. Because of this design the sample preparation is greatly simplified and drilling into the sample is not required. A special device is available for applying the appropriate force when pressing the probe onto the surface of the sample.

We are continiously extending or capacities to measure thermal rock properties. Currently, a laboratory device is under construction allowing for dry and saturated rocks measurements at pressures and temperatures that are simultaneously raised to 250 MPa and 250 °C, respectively.

Read more: http://www.itherlab.science

Contact

Sven Fuchs
Scientist
Dr. Sven Fuchs
Geoenergy
Telegrafenberg
Building A 69, Room 302
14473 Potsdam
+49 331 288-1713
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