This paper experimentally investigates the role of high temperature treatment on pore characteristics, permeability, critical Reynolds number, and flow nonlinearity of granite exposed to temperatures of 100~800 °C. First, variations in pore characteristics, porosity, and pore fractal dimension of granite were analyzed using the mercury intrusion method. Then, a number of water flow tests were conducted on the samples with confining pressures varying from 10 to 30 MPa. The results show that (i) the cumulative pore volume of granite shows an increase with temperatures, which first increases gradually in the range of 100~400 °C, and increases significantly in the range of 400~800 °C. The pore structure becomes developed gradually; (ii) as the temperature increases from 100 to 800 °C, the pore fractal dimension decreases by 12.09%, indicating gradually weaken complexity of pore distributions. An exponential function is used to evaluate the increasing porosity of rock based on the temperature levels; (iii) the relations between volume flow rate and pressure gradient can be well described using the Forchheimer’s law. Both linear and nonlinear coefficients increase with the confining pressure. The equivalent permeability experiences an exponential increase with the temperature due to thermally induced defects; (iv) by defining a critical nonlinear effect factor of 10%, the critical pressure gradient was calculated, which increases with the confining pressure. The critical Reynolds number shows a decrease of 25.49%~67.74% with confining pressure due to more isolated contact areas and tortuous flow paths but increases by a factor of 5.97~17.24 with the temperature. A three-order polynomial function is used to analyze the decrease in transmissivity versus the pressure gradient. The Forchheimer’s law results are evaluated by plotting the normalized transmissivity against the pressure gradient, and an increase in the temperature generally shifts the fitted curves downward.

中文翻译：

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高温下花岗岩的孔隙特征和非线性流动行为

本文实验研究了高温处理对暴露于100〜800°C温度下花岗岩的孔隙特性，渗透性，临界雷诺数和流动非线性的影响。首先，使用压汞法分析了花岗岩的孔隙特征，孔隙率和孔隙分形维数的变化。然后，在围压为10到30 MPa的范围内对样品进行了许多水流测试。结果表明：（i）花岗岩的累积孔体积随温度的升高而增加，首先在100〜400°C范围内逐渐增加，然后在400〜800°C范围内显着增加。孔结构逐渐发展。（ii）随着温度从100升高到800°C，孔的分形维数减小了12.09％，表明逐渐减弱了孔隙分布的复杂性。指数函数用于根据温度水平评估岩石的孔隙度；（iii）体积流量和压力梯度之间的关系可以使用福希海默定律很好地描述。线性系数和非线性系数都随围压而增加。由于热引起的缺陷，等效磁导率随温度呈指数增长。（iv）通过将临界非线性影响因子定义为10％，计算出临界压力梯度，该临界压力梯度随围压而增加。由于更多的隔离接触区域和曲折的流动路径，临界雷诺数在围压下显示减少了25.49％〜67.74％，但是随着温度的升高，增加了5.97〜17.24。三阶多项式函数用于分析透射率与压力梯度的关系。通过绘制归一化的透射率对压力梯度的曲线来评估Forchheimer定律的结果，温度的升高通常会使拟合曲线向下移动。