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INTRODUCTION AND OBJECTIVES:
The thermal conductivity and thermal diffusivity are two physical properties of rock materials that are related to how thermal energy is
transmitted through them, and so they also fundamental to describe and understand energy transfer in soil and, in particular, in perma-
frost areas. Thermal conductivity is a measure of the efficiency with which materials conduct heat energy; thermal diffusivity measures
the efficiency with which materials lose or absorb energy. For isotropic and homogeneous materials thermal conductivity () can be de-
fined by the quotient between the rate at which heat is conducted through the unit area (q) and the temperature gradient or the change in
the temperature with depth (∆T).
The thermal diffusivity (α) depends on the thermal conductivity () according to the following expression:
where ρ is the density and Cp is the specific heat.
Thermal conductivity of rocks depends on several factors among which are mineralogy, chemical composition, porosity and fluid type
in the pores, pressure, temperature, texture, structure, degree of consolidation, alteration, etc.
Under the framework of the program “New generation of polar scientists” of Caixa Geral de Depósitos, the project “Petrophysical char-
acterization of rock and soil samples in relation to permafrost and climate change in Antarctica” was granted a scholarship to me meas-
ure thermal conductivities and thermal diffusivities of cores from boreholes drilled in the Island of Livingston in Maritime Antarctica.
Here the results of the first measurements performed in cores collected from boreholes drilled in January and February, 2008, are pre-
sented. The two boreholes are 5 and 6 meters deep and are located near the Bulgarian Antarctica Base (BAB) of St. Kliment Ohridski,
on northwest of Hurd Peninsula of Livingston Island (Figures 1, 2, 3 and 4). The boreholes were drilled with continuous coring to col-
lect as many samples as possible for laboratory studies. One of the boreholes is located in a CALM site with coordinates 60º21’44.3’’W
62º38´48.5’’S (Figures 1 and 3) and the other is located in a place called PAPAGAL, with coordinates 60º21’49.3’’W 62º38’54.2’’S
(Figure 2 and 3).
PHYSICAL PROPERTIES OF ROCKS COLLECTED IN TWO BOREHOLES DRILLED IN LIVINGSTON ISLAND, MARITIME ANTARCTICA: A STARTING DATA BASE
António Correia (1), Paulo Amaral (2), Gonçalo Vieira (3), Miguel Ramos (4), and Alexandre Trindade (5)
(1) Department of Physics and Geophysical Centre of Evora, University of Evora, Evora, Portugal ([email protected]), (2) Geophysical Centre of Evora, University of Evora, Evora, Portugal ([email protected]), (3) Centre for Geographical Studies, University of Lisbon, Lisbon, Portugal ([email protected]), (4) Department of Physics, University of Alcalá, Madrid, Spain ([email protected]), (5) Centre for Geographical Studies, University of Lisbon, Lisbon, Portugal ([email protected])
THERMAL CONDUCTIVITY AND THERMAL DIFFUSIVITY
MEASUREMENTS:
The cores obtained in the boreholes are identified using the following code (see Table 1): the first letter and digit refers to
the box where the cores are stored; after the dot, the second number refers to the order location in the box. According to the
drilling process the depth of the cores are estimated with an error of about 20 cm.
The determination of the thermal conductivity and the thermal diffusivity of the cores from the two boreholes were made us-
ing a TCS Lippmann & Rauen GbR equipment. The measurements were made in three orthogonal directions (a, b, and c), as
shown in Figure 5, with the cores dry.
RESULTS AND ANALYSIS:
Table 1 shows the values of the thermal conductivity, the thermal diffusivity, and the heat production for cores obtained in
the boreholes drilled in January, 2008, in the CALM site (Figure 1 and 3) and the PAPAGAL site (Figure 2 and 3).
CONCLUSIONS:
The thermal conductivity and thermal diffusivity values measured in cores from two boreholes drilled in the Island of Livingston confirm that the area where the boreholes
were drilled correspond to outcrops of metamorphic rocks (Schön, 1996), which is consistent with local geology.
The highest values of thermal conductivity were measured in the cores from the PAPAGAL site; the CALM site has the highest thermal diffusivity value and the lowest thermal
conductivity value.
The results presented here are preliminary and are far from been completed. There are porosity estimations being done to calculate the thermal conductivity values for the cores
with the pores filled with water and ice, which correspond to the climatic environment of the area where the boreholes were drilled.
Schön, J. H. (1996). Physical properties of rocks: fundamentals and principals of petrophysics (Vols. Handbook of geophysical exploration. Section I, Seismic exploration. v. 18). Oxford, Pergamon, 583.
REFERENCE:
The values of thermal conductivity measured in the cores of the CALM site (Table 1) vary between 2.78 W/mK and 3.36 W/mK and in PAPAGAL site vary between 2.95 W/
mK and 3.57 W/mK. The thermal conductivity average for the CALM site is 3.14 ± 0.15 W/mK and in PAPAGAL site is 3.17 ± 0.17 W/mK.
The values of thermal diffusivity measured in the CALM site (Table 1) vary between 1.49 x 10-6 m2/s and 1.67 x 10-6 m2/s and in the PAPAGAL site between 1.34 x 10-6 m2/s
and 1.64 x 10-6 m2/s. The thermal diffusivity average for the CALM site is 1.58 x 10-6 ± 0.04 x 10-6 m2/s and for the PAPAGAL site is 1.52 x 10-6 ± 0.05 x 10-6 m2/s.
Table 1 also shows the values of the heat production for the two boreholes. A SILENA gamma-ray spectrometer was used to determine the contents in uranium, thorium and
potassium from bits of the cores from the two boreholes. For each borehole those values are presented as well as the heat production values which are 1.30 µW/m3 for the
borehole in the CALM site and 0.70 µW/m3 for the borehole in the PAPAGAL site.
The boreholes distance from each other coarse 187 metres. The variations on thermal conductivity on booth boreholes according to the cores deep are shown on Figures 6 and
7. The different colours represent the boreholes and the shapes represent the measures realized according to the axis.
Figure 1: General view of the CALM site.
Figure 2: General view of the Papagal site.
Figure 3: Location of the CALM
and Papagal sites.
Figure 5: Directions of
measurement of the ther-
mal conductivity and the
thermal diffusivity.
Table 1: Thermal conductivity, thermal diffusivity (dry samples), and heat production values
for the cores collected in the CALM and Papagal sites boreholes, Livingston Island. TCa,
TCb, and TCc, and, TDa, TDb, and TDc refer to the measurement directions of thermal con-
ductivity and thermal diffusivity, respectively, along (a), (b), and (c) directions of Figure 5.
Figure 4: Drilling in Livingston Island.
ACKNOWLEDGEMENTS:
The authors thank the Fundação para a Ciência e a Tecnologia for funding the project PERMANTAR which allowed to collect the cores used in the presentation and process the data. One of the
authors (PMA) acknowledges the grant of Caixa Geral de Depósitos.
Figure 7: Average Thermal conductivity and average thermal diffusivity values for the CALM and PAPAGAL sites ac-cording to core depth.
Figure 6: Thermal conductivity values for the CALM and PA-PAGAL sites according to core depth.
D
A B
C
