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.

中文翻译：

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矿物非均质砂岩基质和体热导率的孔隙液依赖性控制

对于各种地热工程应用，经常使用唯一可间接确定的基体导热率（λm）将测得的空气饱和砂岩的块岩导热率（λb）转换为水饱和条件。然而，无论存在何种孔隙流体，λm的绝对值保持恒定的必要假设在实践中均无效，并且尚未针对不同的孔隙流体证明λm的明确控制因素。孔隙流体控制的λm值变化还质疑了经验代理模型在对水饱和的λb进行校准时估计水饱和的λb的可传递性。这项研究对定量的矿物成分数据和孔隙度（Φ）进行了多元回归分析，以确定不同类型的孔隙流体（水与空气饱和度）的λm控制值。此外，还要检查由不同的计算方法或输入数据（理论几何平均模型或矿物组成数据）得出的λm值的差异。对于孔隙流体类型，我们进一步测试了不同砂岩特性作为潜在代理估算λb的适用性。来自不同测量条件（空气饱和或水饱和）的砂岩λm绝对值差异最可能与孔隙空间中自生高岭石的形成有关，这是由于碱长石的变化引起的。此外，岩石基质的热特性主要由石英和白云石等高导热矿物组分的体积分数控制。仅以Φ或P波速度（vp）作为变量的经验模型不适合预测砂岩的水饱和λb。相反，必须包括高导热矿物相（例如石英和白云石）的定量矿物学数据。易于测量的vp被提议作为两种测试的孔隙流体的有前途的代理：结合空气饱和砂岩的总石英体积/孔隙率比，以及结合水饱和砂岩的石英和白云岩体积分数。仅以Φ或P波速度（vp）作为变量的经验模型不适合预测砂岩的水饱和λb。相反，必须包括高导热矿物相（例如石英和白云石）的定量矿物学数据。易于测量的vp被提议作为两种测试的孔隙流体的有前途的代理：结合空气饱和砂岩的总石英体积/孔隙率比，以及结合水饱和砂岩的石英和白云岩体积分数。仅以Φ或P波速度（vp）作为变量的经验模型不适合预测砂岩的水饱和λb。相反，必须包括高导热矿物相（例如石英和白云石）的定量矿物学数据。易于测量的vp被提议作为两种测试的孔隙流体的有前途的代理：结合空气饱和砂岩的总石英体积/孔隙率比，以及结合水饱和砂岩的石英和白云岩体积分数。