Kämmlein M, Stollhofen H (2019)
Publication Language: English
Publication Type: Journal article, Original article
Publication year: 2019
Book Volume: 7:13
URI: https://geothermal-energy-journal.springeropen.com/articles/10.1186/s40517-019-0129-4
DOI: 10.1186/s40517-019-0129-4
Open Access Link: https://geothermal-energy-journal.springeropen.com/articles/10.1186/s40517-019-0129-4
For a variety of geothermal engineering applications, the only indirectly determinable
matrix thermal conductivity (λm) is frequently used to convert the measured
bulk rock thermal conductivity (λb) of air-saturated sandstones to water-saturated
conditions. However, the necessary assumption that the absolute value of λm remains
constant irrespective of the pore fluid present turns out to be not valid in practice and
the explicit control factors on λm have not been demonstrated yet for different pore
fluids. A pore fluid-controlled change in the λm value also questions the transferability
of empirical proxy models for the estimation of water-saturated λb when they were
calibrated on air-saturated samples. This study applies a multiple regression analysis to
quantitative mineralogical composition data and porosity (Φ) to identify the controls
of the λm for different types of pore fluids (water- vs. air-saturation). In addition, the
differences in the calculated λm values resulting from different calculation methods or
input data (theoretical geometric mean model or mineralogical composition data) are
examined. We further test the suitability of different sandstone properties as potential
proxies for the estimation of the λb, with respect to the pore fluid type. Differences in
the absolute value of λm of sandstones from different measurement conditions (air- or
water-saturated) are most probably related to the formation of authigenic kaolinite in
the pore space, originating from the alteration of alkali feldspar. In addition, the thermal
properties of the rock matrix are mainly controlled by the volume fractions of the high
thermally conductive mineral fractions quartz and dolomite. Empirical models that
have solely Φ or P-wave velocity (vp) as variables are not suitable for the prediction of
water-saturated λb of sandstones. Instead, quantitative mineralogical data of high thermally
conductive mineral phases such as quartz and dolomite have to be included. The
easily measureable vp is proposed as a promising proxy for both pore fluid types tested:
combined with the total quartz volume/porosity ratio for air-saturated sandstones,
and combined with the quartz plus dolomite volume fractions for water-saturated
sandstones.
APA:
Kämmlein, M., & Stollhofen, H. (2019). Pore‑fluid‑dependent controls of matrix and bulk thermal conductivity of mineralogically heterogeneous sandstones. Geothermal Energy, 7:13. https://doi.org/10.1186/s40517-019-0129-4
MLA:
Kämmlein, Marion, and Harald Stollhofen. "Pore‑fluid‑dependent controls of matrix and bulk thermal conductivity of mineralogically heterogeneous sandstones." Geothermal Energy 7:13 (2019).
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