温度作用后花岗岩微观孔隙结构和渗透率的研究

Study on Microscopic Pore Structure and Permeability of Granite After Temperature Action

为了研究温度作用下花岗岩的孔隙结构和渗流特性,对热处理后(25~600℃)的花岗岩试件进行了扫描电镜测试、高压压汞实验和渗流实验,从扫描电镜的镜下特征、毛管压力曲线形态特征、孔容、孔径分布、孔隙度、渗透率等多方面进行了研究,修正了常规的渗透率预测模型,对模型计算渗透率与实测渗透率进行了对比分析。研究结果表明:花岗岩内部含有初始微裂隙和孔洞,孔洞形状不规则;随着温度升高,花岗岩孔喉不断发育,花岗岩压汞曲线中进汞曲线逐渐变得平滑,退汞率逐渐升高,试件中微孔、过渡孔、中孔、大孔的孔容和总孔容总体逐渐增大,孔径分布范围扩大,连通性增强,孔隙度呈现增大趋势;花岗岩渗透率随温度总体呈指数函数增加,400℃之后渗透率大幅增大;试件中大孔数量增加是花岗岩渗透率大幅提升的主要原因;对高温花岗岩而言,利用修正的Winland模型得到渗透率的预测值和实验测试值较接近,表明孔喉半径特征值、孔隙度共同影响下花岗岩的渗透率模型更为合理。研究结果将为高温岩体地热开发工程的方案设计提供一定的理论基础。

To investigate the effect of temperature on the pore structure and seepage characteristics of granite,samples were subjected to a scanning electron microscopy(SEM)test,a high-pressure mercury injection test and a seepage test.From SEM of the microscopic characteristics,morphological characteristics of the capillary pressure curve,entrance,pore size distribution,porosity,permeability and other aspects are stu-died.The conventional permeability prediction models have been corrected,and the calculated permeability and measured permeability are compared and analysed.The results showed that there were initial micro-cracks and pores in the granite,with irregular pore shapes.With the increase in temperature,the pore throat of the granite develops continuously as the temperature rises,and the mercury inflow curve in the granite mercury injection curve becomes smoother,and the mercury removal rate gradually increases.The pore volume and total pore volume of micropores,mesopores and transition pores in the sample gradually become larger,the pore size distribution range expands,the connectivity enhances and the porosity increases.Granite’s permeability generally increases exponentially with temperature and increases greatly after 400℃.The increase in the number of large pores in the sample is the primary reason for the increased permeability of granite.The permeability predicted by the modified Winland model for high-temperature granite is close to the permeability tested by the experiment,indicating that the granite permeability model is more reasonable under the combined influence of the characteristic value of pore-throat radius and porosity.The research results will provide a theoretical basis for the scheme design of high-temperature rock mass geothermal development engineering.