砂岩和灰岩热导率温度作用效应的实验研究

Research on the Thermal Conductivity of Sandstone and Limestone after High Temperature Treatment

高温作用会导致岩石内部结构发生变化,并对其热物理性质产生显著影响,因此,研究高温作用后岩石热物理性质的变化规律对地热系统及存在热流传播问题的地下工程具有指导意义。实验以高温作用后砂岩、灰岩为研究对象,利用热常数分析仪研究了砂岩、灰岩热导率随温度的变化特征,并结合岩石微观结构特性,从矿物受热的微观机理出发,对岩石热导率变化的内在机理进行了初步探讨。结果表明,砂岩热导率可分为25~100℃、100~400℃、400~600℃和600~900℃四个阶段,灰岩热导率可分为25~100℃和100~400℃两个阶段,砂岩、灰岩在25~400℃间由于水分的蒸发热导率整体变化较快,400℃以后矿物发生相变及分解、熔融等物理化学反应,从而微裂缝发育、延伸,并连接形成宏观裂隙,砂岩热导率急剧下降,灰岩内部结构较完整,微裂隙发育较少,热导率基本稳定。

The internal structure of the rock(such as mineral composition, pore characteristics and micro cracks) will change after high temperature treatment, which also has a significant effect on its thermal physical properties. Therefore, the research on the changes of the thermal physical properties of rocks after high temperature heating can give guidance to the management of geothermal system and the underground project with heat flow transmission. In this investigation, high temperature furnace and hot disk thermal constant analyzer were used to measure the thermal conductivity of sandstone and limestone after high temperature heating. Combined with the microstructure characteristics of rocks and the heating behavior of minerals, the inner mechanism of the change of thermal conductivity of these rocks was discussed. The results show that the thermal conductivities of the sandstone and limestone decrease with the increase of temperature. The variation of thermal conductivity of sandstone can be divided into four stages: 25 to 100℃, 100 to 400℃, 400 to600℃and 600 to 900℃. The variation of thermal conductivity of limestone can be divided into two stages: 25 to 100℃and 100 to400℃. From 25 to 400℃, the thermal conductivity of both sandstone and limestone change rapidly due to the evaporation of water.Physical and chemical reactions(such as mineral expansion, decomposition, oxidation-reduction and melting) and phase transformation occur in the minerals when the temperature exceeds 400℃. Meanwhile, the micro cracks would develop, extend and connect to form the macro cracks. Therefore, the thermal conductivity of sandstone decreases sharply. However, the thermal conductivity of limestone keeps stable due to its structural integrity(few micro cracks developing).