Simultaneous determination of thermal conductivity, thermal diffusivity and specific heat in sI methane hydrate

Thermal conductivity, thermal diffusivity and specific heat of sI methane hydrate were measured as functions of temperature and pressure using a needle probe technique. The temperature dependence was measured between −20°C and 17°C at 31.5 MPa. The pressure dependence was measured between 31.5 and 102 MPa at 14.4°C. Only weak temperature and pressure dependencies were observed. Methane hydrate thermal conductivity differs from that of water by less than 10 per cent, too little to provide a sensitive measure of hydrate content in water-saturated systems. Thermal diffusivity of methane hydrate is more than twice that of water, however, and its specific heat is about half that of water. Thus, when drilling into or through hydrate-rich sediment, heat from the borehole can raise the formation temperature more than 20 per cent faster than if the formation's pore space contains only water. Thermal properties of methane hydrate should be considered in safety and economic assessments of hydrate-bearing sediment.     

Thermal conductivity of reinforced soils: A literature review

This paper aims a review of the literature related to soil reinforcements to achieve lower soil thermal conductivity （2）. The use of various natural and synthetic fibers, polymers, geosynthetics, agricultural waste/materials, and nanoclays is discussed and existing prediction models that have been thought to affect low thermal conductivity are presented.     

黄土高原典型塬区土壤热状况研究

在陆-气相互作用中,土壤热状况（土壤温度、土壤导热率等）和土壤湿度等陆面状况对大气环流和气候变化都有着重要影响。黄土高原横跨干旱、半干旱及半湿润地区,为我国第二大高原,幅员辽阔。该复杂下垫面上的陆-气相互作用不仅直接影响到黄土高原地区的气候和环境变化,而且对东亚、乃至全球的气候和环境变化都可能产生重要影响。而对黄土高原区域的土壤热状况及土壤温度的研究是黄土高原陆-气相互作用研究的重要组成部分。分析了黄土高原典型塬区不同下垫面的土壤温度状况,分析了造成各种下垫面温度分布和变化不同的原因,得到如下结论：在近地层,随着土壤深度的增加,土壤温度振幅逐渐减小,40 cm土壤温度相对以上各层变化不明显。就季节变化而言,土壤温度在1 a中有两次稳定状态。第一次出现在4月上旬,其值约为6 ℃左右;第二次出现在11月中旬,温度值为14 ℃。相对于全年土壤温度而言,在12月到次年2月有一个低温中心,温度低于零度;7～8月间有一个暖中心。各层土壤温度在1月份是最低的,其后一路上升,4、5月份是土壤温度快速上升期,至8月上旬土壤温度达到最大值,为土壤升温期;其后温度开始下降。土壤温度梯度具有明显的日变化特征,夜间,土壤的热量是从深层传向地表的,而随着太阳高度角的加大,土壤温度梯度转为负值,深层土壤从地表获得能量,到了傍晚19时左右,温度梯度又转为正值;土壤温度梯度的变幅在有植被时要明显小于无植被时。各站的日平均土壤导热率,柴寺、塬下和中心站分别是1.43,1.24,1.17 W·m^-1·k^-1,土壤物理性质和土壤质地的不同是各站土壤温度分布和土壤热传导率存在差异的原因之一。     

On the importance of rock thermal conductivity and heat flow density in basin and petroleum system modelling

Basin and petroleum systems are routinely modelled to provide qualitative and quantitative assessments of a hydrocarbon play. The importance of the rock thermal properties and heat flow density in thermal modelling the history of a basin are well-known, but little attention is paid to assumptions of the thermal conductivity, present-day heat flow density and thermal history of basins. Assumed values are often far from measured values when data are available to check parameters, and effective thermal conductivity models prescribed in many basin simulators require improvement. The reconstructed thermal history is often justified by a successful calibration to present-day temperature and vitrinite reflectance data. However, a successful calibration does not guarantee that the reconstruction history is correct. In this paper, we describe the pitfalls in setting the thermal conductivity and heat flow density in basin models and the typical uncertainties in these parameters, and we estimate the consequences by means of a one-dimensional model of the super-deep Tyumen SG-6 well area that benefits from large amounts of reliable input and calibration data. The results show that the entire approach to present-day heat flow evaluations needs to be reassessed. Unreliable heat flow density data along with a lack of measurements of rock thermal properties of cores can undermine the quality of basin and petroleum system modelling.     

Thermal Properties of a Supraglacial Debris Layer with Respect to Lithology and Grain Size

This paper focuses on the impacts of debris cover on ice melt with regards to lithology and grain size. Ten test plots were established with different debris grain sizes and debris thicknesses consisting of different natural material. For each plot, values of thermal conductivity were determined. The observations revealed a clear dependence of the sub‐debris ice melt on the layer thickness, grain size, porosity and moisture content. For the sand fraction the moisture content played a dominant role. These test fields were water saturated most of the time, resulting in an increased thermal conductivity. Highly porous volcanic material protected the ice much more effectively from melting than similar layer thicknesses of the local mica schist. However, the analysis of thermal diffusivities demonstrated that the vertical moisture distribution of the debris cover must be taken into consideration, with the diffusivity values being significantly lower in deeper layers.     

Accounting for mineralogical composition and origin of soils and sedimentary rocks in thermal property predictions

A methodology for calculating the thermal conductivity of soils and rocks is developed which takes into account their origin and mineralogical composition.This method utilizes three approaches.One is founded on the structural modeling of contact heat interaction between particles and fills and estimates the statistical probability distribution of the particles in the volume of the medium.The second approach analyses perturbation to the temperature field of the matrix medium by ellipsoidal inclusions.The third approach is to find the mean thermal conductivity of the solid skeleton in the universal model at different composition of rock-forming minerals.     

Permafrost distribution and temperature in the Elkon Horst,Russia

The Elkon Horst is a geological structure that consists of heterogeneous strata with highly variable geocryological and temperature conditions. Gaining accurate knowledge of permafrost distribution patterns within this structure is of both scientific and practical importance. In mountainous terrain, the ground thermal regime is controlled by both surface and subsurface conditions. Surface conditions include snow cover characteristics, the presence or absence of vegetation, vegetation density, etc.. In contrast, subsurface conditions involve rock lithology or petrography, density, quantity and depth of fissures, groundwater, etc.. This article examines ground thermal regimes in various geomorphological settings based on temperature measurement data from geotechnical boreholes. The occurrence and extent of permafrost were evaluated for the entire horst area using direct and indirect methods. The maximum permafrost thickness measured in the Elkon Horst is 330 m, and the estimated maximum is 450 m at higher elevations. Thermophysical properties were determined for the major rock types, and the geothermal heat flux was estimated for the study area. The thermal conductivities were found to vary from 1.47 to 4.20 W/(m·K), and the dry bulk densities to range between 2,236 kg/m~3 and 3,235 kg/m~3. The average geothermal heat flux was estimated to be 44 mW/m~2.     

A stochastic model to quantify the steady-state crustal geotherms subject to uncertainties in thermal conductivity

In this communication the 1-D steady-state heat conduction problem is solved in a stochastic framework incorporating uncertainties in the depth-dependent thermal conductivity. For this purpose, a new approach to the perturbation method, an expansion series method, which allows for the incorporation of a large variance in the controlling parameters, has been used. This method helps in avoiding assumptions on the probability distribution of the parameter and instead uses information pertaining to the mean and spatial correlation structure. This information is easily available in most geological situations and hence the thermal conductivity is assumed to have a Gaussian coloured noise correlation structure. With this information the stochastic heat conduction equation in equilibrium is solved and analytical expressions for the first two moments, that is, the mean and variance of the temperature field, are obtained. The expression for variance shows that it is highly dependent on the coefficient of variability of thermal conductivity, on the correlation length scale and on the depth. The methodology developed has been applied to quantify the steady-state geotherms, along with their associated error bounds, on a standard crustal model.     

Joint three-dimensional inversion of coupled groundwater flow and heat transfer based on automatic differentiation: sensitivity calculation, verification, and synthetic examples

Inverse methods are useful tools not only for deriving estimates of unknown parameters of the subsurface, but also for appraisal of the thus obtained models. While not being neither the most general nor the most efficient methods, Bayesian inversion based on the calculation of the Jacobian of a given forward model can be used to evaluate many quantities useful in this process. The calculation of the Jacobian, however, is computationally expensive and, if done by divided differences, prone to truncation error. Here, automatic differentiation can be used to produce derivative code by source transformation of an existing forward model. We describe this process for a coupled fluid flow and heat transport finite difference code, which is used in a Bayesian inverse scheme to estimate thermal and hydraulic properties and boundary conditions form measured hydraulic potentials and temperatures. The resulting derivative code was validated by comparison to simple analytical solutions and divided differences. Synthetic examples from different flow regimes demonstrate the use of the inverse scheme, and its behaviour in different configurations.