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Characterization of rock thermal conductivity by high-resolution optical scanning

Geothermics

By:
, , , , and
DOI: 10.1016/S0375-6505(99)00007-3

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Abstract

We compared thress laboratory methods for thermal conductivity measurements: divided-bar, line-source and optical scanning. These methods are widely used in geothermal and petrophysical studies, particularly as applied to research on cores from deep scientific boreholes. The relatively new optical scanning method has recently been perfected and applied to geophysical problems. A comparison among these methods for determining the thermal conductivity tensor for anisotropic rocks is based on a representative collection of 80 crystalline rock samples from the KTB continental deep borehole (Germany). Despite substantial thermal inhomogeneity of rock thermal conductivity (up to 40-50% variation) and high anisotropy (with ratios of principal values attaining 2 and more), the results of measurements agree very well among the different methods. The discrepancy for measurements along the foliation is negligible (<1%). The component of thermal conductivity normal to the foliation reveals somewhat larger differences (3-4%). Optical scanning allowed us to characterize the thermal inhomogeneity of rocks and to identify a three-dimensional anisotropy in thermal conductivity of some gneiss samples. The merits of optical scanning include minor random errors (1.6%), the ability to record the variation of thermal conductivity along the sample, the ability to sample deeply using a slow scanning rate, freedom from constraints for sample size and shape, and quality of mechanical treatment of the sample surface, a contactless mode of measurement, high speed of operation, and the ability to measure on a cylindrical sample surface. More traditional methods remain superior for characterizing bulk conductivity at elevated temperature.Three laboratory methods including divided-bar, line-source and optical scanning are widely applied in geothermal and petrophysical studies. In this study, these three methods were compared for determining the thermal conductivity tensor for anisotropic rocks. For this study, a representative collection of 80 crystalline rock samples from the KTB continental deep borehole was used. Despite substantial thermal inhomogeneity of rock thermal conductivity and high anisotropy, measurement results were in excellent agreement among the three methods.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Characterization of rock thermal conductivity by high-resolution optical scanning
Series title:
Geothermics
DOI:
10.1016/S0375-6505(99)00007-3
Volume
28
Issue:
2
Year Published:
1999
Language:
English
Publisher:
Elsevier Science Ltd
Publisher location:
United Kingdom
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geothermics
First page:
253
Last page:
276
Number of Pages:
24