Poster EGU 2011
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This document summarizes a study that measured physical properties of cores from a 15m borehole in Livingston Island, Antarctica. Thermal conductivity and diffusivity were measured on dry cores and varied between 3.02-3.32 W/mK and 1.42-1.64 x 10-6 m2/s respectively. Porosity was low at 1.1-1.8% and density ranged from 2640-2666 kg/m3. Heat production across the borehole was 1.698 亮W/m3. Temperature measurements showed an average annual temperature of -1.76属C with a thermal amplitude of 7.71属C. The cores were composed of sandstone. Physical
Poster EGU 2011
- 1. INTRODUCTION Polar regions are being affected by climate change and, as a result, changes in the thickness and distribution of permafrost and active layer are observed at high latitudes. Thermal conductivity and the thermal diffusivity of the uppermost ground are important physical properties to understand time and space evolution of the temperature in permafrost areas, as well as freezing and thawing. In 2007, a 15 m deep borehole (Figure 1) was drilled in the surrounding of Reina Sofia peak (276 a.s.l.) just on the Hurt glacier, in Livingston Island, Shetland Islands. The borehole, named Permamodel-Gulbenkian 2 (PG2), has as coordinates 60尊22卒50,102卒卒 and 62尊40卒10,063卒卒. Cores from the borehole were collected to measure the thermal conductivity and the thermal diffusivity with the idea of estimating the heat flow density. METODOLOGY AND RESULTS The thermal conductivity and thermal diffusivity values were measured with a TCS Lippmann & Rauen Gbr (Figure 2D) by transient methods; The values of thermal conductivity in dry cores vary between 3.02 W/m.K and 3.32 W/m.K (Table 1); the values of the thermal diffusivity vary between 1.42 x 10-6 m2s-1 and 1.64 x 10-6 m2s-1 (Table 2); the average heat production for the entire borehole is 1.698 亮W.m-3 (Table 1). The values from porosity and density were calculated using the bulk volume, obtain by buoyancy techiniques and using pore volume, obtain by water saturation techiques (Figure 2A, 2B, and 2C). The values of the density vary between 2640 kg/m3 and 2666 kg/m3 and the values of porosity vary between 1.1% and 1.8%. In order to calculate the heat production per volume, a SILENA gamma-ray spectrometer was used to determine the contents in uranium, thorium, and potassium. The heat production (HP) calculated for the borehole is 1.698 袖W/m3. A petrographic study of the cores indicate that they are sandstones (Figure 3). DISCUSSION AND CONCLUSIONS The porosities measured in the core of PG2 borehole are very low (less than 1.8%, (Table 1)). Because of the low porosity, thermal conductivity and thermal diffusivity remain constant along the year, as the temperature change closely to 0尊C. The values of heat production per unit volume are also low and so this parameter was neglected to the contribution to the regional heat flow density. The values of the heat flow density cannot be estimated at this stage because it is not possible to obtain the stationary component of the thermal signal in the borehole yet (Table 2). However, the values of thermal conductivity (Table 1) can be used in future to estimate the heat flow density in the Reina Sofia Mountain. Physical properties of cores from a 15 m deep borehole in Reina Sofia Mountain, Livingston Island, Maritime Antarctica Paulo Maciel Amaral, amaral.paulomaciel@gmail.com (1), Ant坦nio Correia, correia@uevora.pt (1), Gon巽alo Vieira, vieira@campus.ul.pt (2), Miguel Ramos, miguel.ramos@uah.es (3), and Alexandre Trindade, alexandretn@gmail.com (2) (1) Geophysical Centre of Evora, University of Evora, Evora, Portugal, (2) Centre for Geographical Studies, University of Lisbon, Lisbon, Portugal, (3) Department of Physics, University of Alcal叩, Madrid, Spain. EGU2011-7670 Figure 1: Drilling in the surrounding of Reina Sofia Peak and location of the PG2 borehole in Livingston Island, Shetland Islands, Maritime Antarctica. = . (1) The heat flow density is defined on the Fourier equation, where (T), is the temperature gradient, and K is the thermal conductivity. Some times the heat transfer can be affected by the internal heat produced by rocks (HP). Table 1: Thermal conductivity (TC) and Thermal diffusivity (TD) values, and Uranium (Cu), Thorium (Cth) and Potassium (Ck) contents, porosity and density. Kd is the value of thermal conductivity measured in dry cores; Kd is the value of thermal conductivity calculated with saturated pore with water and Kf is the value of thermal conductivity calculated with saturated pore with ice. A is the het production per unit volume. (*) Since the thermal conductivity of rocks is highly dependent on porosity, this parameter was also used to estimate, the thermal conductivity of the cores saturated with water (Ks) and ice (Kf), (Table 1). Depth (m) Average temperaute (尊C) Minimum temperature (尊C) Maximum temperature (尊C) T (尊C/m) 0.2 -2.957 -9.528 7.544 1.795 0.4 -2.598 -8.461 4.642 -0.174 0.8 -2.668 -7.463 2.603 0.289 1.2 -2.552 -6.413 1.646 -0.182 1.6 -2.625 -5.947 1.084 1.722 2.0 -1.936 -4.979 1.048 -0.350 2.5 -2.111 -4.404 0.636 -0.221 3.0 -2.221 -4.469 0.061 -0.087 3.5 -2.265 -3.899 -0.380 0.880 4.0 -1.825 -3.414 0.111 0.125 5.0 -1.700 -2.862 -0.346 -0.095 6.0 -1.795 -2.929 -0.410 -0.162 8.0 -2.120 -2.936 -1.422 0.350 10.0 -1.419 -1.902 1.119 -0.199 12.5 -1.917 -2.399 -1.897 0.041 15.0 -1.815 -1.884 -0.376 Table 2: Annual temperatures PG2 borehole during the year 2009 (01/01/2009 to 31/12/2009). Average annual temperature, annual minimum temperature and annual maximum temperature are presented. The values of average annual temperatures are calculated from the daily average temperature. The values of the minimum and maximum temperatures correspond to the annual minimum and maximum values obtained at the depths in the table. Figure 3: Sandstone of PG2 . -15 -10 -5 0 5 10 1 101 201 301 0,20 Deph(m) Deph(m) Temperaute(尊C) Figure 4: Change of the daily average temperatures in the soil of the PG2 site between 01/01/2009 and 12/31/2009 PG2. A) Soil temperature at 0.20 m depth (yellow line). B) surface isotherms (属C). C) Model developed in Matlab based on the heat equation in one dimension, using the average daily temperature of soil at 0.20 m depth (1,76 尊C) and thermal amplitude of 7.71 属C. Mean thermal diffusivity: 1.54 x 10-6 m2/s (time in months). Figure 2: A), B) and C) Material used to obtain the values for the porosity and density determinations; D) TCS Lippmann & Rauen GbR equipment for thermal conductivity and diffusivity measurements. Acknowledgments: The authors thank the Funda巽達o para a Ci棚ncia e Tecnologia for funding the project PERMANTAR and Funda巽達o Calouste Gulbenkian for funding the drilling of PG2 borehole. Dr. Jan Safanda has measured the thermal conductivities and heat productions of the cores. Thanks to the Spanish Antarctic Program and the Permamodel project. EGU General Assembly, 2011 April 3 -8, Vienna, Austria Ref. Depth of samples TC (W/m.K) TD (x 10-6 m2 .s-1 ) CU CTh CK A Porosity Density Lithology (m) Kd Ks * Kf* p.p.m. p.p.m. % 袖Wm-3 (%) (kg/m3 ) C7.20 1 3.28 3.41 3.46 1.64 2.69 10.86 2.15 1.698 1.30% 2666 Sandstone C7.60 4.3 3.02 3.12 3.17 1.42 1.10% 2662 Sandstone C7.77 7.6 3.13 3.3 3.38 1.48 1.80% 2640 Sandstone C8.21 10.7 3.32 3.43 3.48 1.6 1.10% 2666 Sandstone C8.42 13.7 3.25 3.4 3.46 1.58 1.50% 2666 Sandstone C8.54 15.4 3.22 3.35 3.4 1.49 1.30% 2652 Sandstone cm cm Months