The Influence of Fold Structure on Heat Accumulation in Hot Dry Rocks

Hot dry rock resources as one of the most promising clean energy in the future, with large reserves, renewable and other advantages, since the 1970 s, many countries all over the world have explored and practiced a lot on the exploration and development of hot dry rock resources, however, few studied the heterogeneity of the rock and the underground geologic structures of hot dry rock resources influence domain enrichment regularity of heat transfer mechanism. Therefore, this article considered the thermal conductivity of rock anisotropy, and set up a horizontal stratum and a fold strata 2D geological model, through numerical simulation with the field rock samples indoor triaxial rock thermal conductivity test results, introducing the thermal conductivity of rock anisotropy index A = K vertical bedding/ K parallel bedding and analyze the underground geologic structures’ influence on heat transfer in the rock. The results show that the anisotropy of rock thermal conductivity has no influence on the heat transfer process in underground rock strata when the rock layer is horizontal, which can be regarded as one-dimensional multilayer wall heat transfer. Fold structure will influence the underground heat transfer direction, so it is not simply seen as a one-dimensional multilayer flat wall heat transfer process in numerical simulation. At the inclined interface of rock strata, "heat flow refraction" usually occurs, which further affects the direction of heat transfer. As a result, heat is concentrated in the syncline of the fold structure in the deep and anticline in the middle and deep layers, while the temperature distribution in the shallow layer is almost unaffected by the structure. The research results of this paper are of great significance to the delineation of the target area and the development and utilization of the hot dry rock resources.

A PREDICTION MODEL OF THERMAL CONDUCTIVITY OF ROCK USING MEASUREMENTS IN BIPHASIC MIXTURES

ABSTRACT. In this study, we developed a model to predict the thermal conductivity of full rocks from measurements on biphasic mixtures of grains of these rocks. Firstly, we measured the density and thermal conductivity of the full rock samples. The full samples were then grounded and we measured the effective thermal conductivity of mixtures prepared with grains of these rocks in different porosities using air as saturating. Using the flexible model of thermal conduction developed in this study, which we call Geoterm, and the rule of generalized mixture due to Korvin, we calculated the average values of the numerical factors of the equations of these two models and, with these equations, we predicted the thermal conductivity of the integrity rock by adjusting the equations of these models with experimental data. Even with these equations and the data of the integrity rocks and mixtures, we predicted the effective thermal conductivity of the samples for the various porosities of the mixtures. The predicted results for the full rock, as compared to the measured values, showed small and large discrepancies due to the large variation range of the thermal conductivity of the full rocks, resulting in ranges also wide for the numerical factors of the two equations. In agreement with Krupiczka empirical expression, the values predicted by the Geoterm and Korvin models for effective thermal conductivity showed lower discrepancies when compared to other models observed in this study.Keywords: rock thermal conductivity, effective thermal conductivity, binary mixture model.RESUMO. Neste estudo, desenvolvemos um modelo para predizer a condutividade térmica de rochas íntegras a partir de medidas em misturas binárias de grãos destas rochas. Primeiramente, medimos a densidade e a condutividade térmica das amostras das rochas íntegras. As amostras foram, em seguida, moídas e medimos a condutividade térmica efetiva de misturas preparadas com os grãos dessas rochas em diferentes porosidades usando ar como saturante. Usando o modelo flexível de condução térmica desenvolvido neste estudo, denominado Geoterm, e a regra da mistura generalizada de Korvin, calculamos os valores médios dos fatores numéricos das equações destes dois modelos e, com estas predissemos a condutividade térmica da rocha íntegra pelo ajuste dos parâmetros desses modelos com os dados experimentais. Ainda com essas equações e com os dados das rochas íntegras, como também das misturas, predissemos a condutividade térmica efetiva das amostras para as várias porosidades das misturas. Os resultados preditos para a amostra íntegra, quando comparados aos valores medidos, apresentaram discrepâncias pequenas e grandes, consequência de a faixa de variação da condutividade térmica das rochas ser bem larga resultando em faixas também largas para os fatores numéricos das duas equações. Em concordância com a expressão empírica de Krupiczka, os valores preditos pelos modelos Geoterm e Korvin para condutividade térmica efetiva mostraram menores discrepâncias quando comparados a outros modelos verificados neste estudo.Palavras-chave: condutividade térmica de rocha, condutividade térmica efetiva, modelo de mistura binária.

Analysis of Impact of Moisture Content on Rock Thermal Conductivity Coefficient Using TCS Method

The coefficient of thermal conductivity scanner (TCS) was used to test granodiorite, sandstone and rhyolite samples, focuses on the changing rule of the thermal conductivity coefficient of rock under different moisture content. The coefficient of thermal conductivity of the rock increases with water content, and follow a linear relationship. The relative thermal conductivity of three kinds of rock sample is: granodiorite higher than sandstone and higher than rhyolite. The higher the structure density at the same time, the smaller the porosity, the stronger the cementation, the higher the strength, the greater the thermal conductivity of rock mass. This conclusion can be used with geothermal energy development, and has certain reference value.

Experimental Analysis on Thermal Conductivity of Rock

This paper carried out the experimental study on the thermal conductivity of rock in different depth by transient hot-strip method and the analysis on the reliability of the data. The results show that thermal conductivity of pelitic siltstone has been less affected by the varying versus depth of the rock stratum than tuff, but the thermal conductivity of tuff slightly higher than pelitic siltstone.

The Key Technical Analysis on the Hot Dry Rock in Northeast Cold in China

Northeast heat supply is an eternal demand, it would cost tens of thousand of moneys for heat supply, on the other hand, the resource of coal and fossil fuels is non-renewable source of energy, in the future it will be consumed, so it is still a serious problem to solve the winter heat supply. At the same time, the hot dry rock has three essential factors including a huge number, renewable and not polluting the environment, which will open up new ways on heat supply in cold area. Based on its advantages the paper will design a heated system more effective than the technology of shallow ground source heat pump, meanwhile analysis the key technology during exploiting the hot dry rock progress, then the thermal conductivity of rock under high temperature and high pressure and the heat transfer ability between rock and water as well as pipe material and insulation technology, all of which will realize the key technology about the dry-heat rock heating. In conclusion, if the key technology on heated system would be settled, it will bring breakthrough about using the hot dry rock on heated supply in cold areas.

Determination of thermal conductivity of rocks samples using fabricated equipment

The aim of the paper is to describe how inexpensive/simple physics equipment was fabricated and used in the determination of thermal conductivity of rock samples. We used the experimental techniques known as transient method of measuring thermal properties of rock samples at ambient temperature. We investigated samples found in five locations/region (Ewekoro, Ile-Ife, Igara, Ago-Iwoye, Abeokuta) in South western Nigeria. Those samples are limestone, dolerite, marble, gneiss, and granite. Although the samples are multi-mineral as revealed by photomicrograph, the thermal conductivity results obtained 1.40, 1.50, 1.57, 1.75, and 2.94 W/m?C, respectively, are found to be consistent with the ones in literature where highly expensive and sophisticated (not easily affordable in developing nation) equipment are used. .