高温三轴应力下粗、细粒花岗岩力学特性研究

Study on the Mechanical Properties of Coarse-grained and Fine-grained Granite Under High Temperature Triaxial Stress

干热岩地热真正开发的是深层的干热岩地热,由于成岩环境的不同,深层花岗岩的矿物组成及细观结构与浅层花岗岩有较大差异。为揭示真正深层花岗岩特性用以指导干热岩地热开发,文章对中国山西芦芽山花岗岩(粗粒花岗岩)及中国山东鲁灰花岗岩(细粒花岗岩)高温(100~400℃)三轴应力下的热、力学特性差异进行了研究。试验得出,粗粒花岗岩热膨胀系数随温度的升高呈线性增加趋势,其热膨胀系数平均为细粒花岗岩的1.52倍,且在400℃时二者差值最大。粗粒花岗岩弹性模量随温度的升高呈先增后减的趋势,其随温度变化的阈值温度为300℃.此外,细粒花岗岩弹性模量为粗粒花岗岩的1.4~2.6倍,且差异会随着温度及围压的升高而增大。经显微观测可知,粗粒花岗岩含有的大量原生裂隙及其极端的非均质性导致了粗粒花岗岩更大的热应变以及更加劣化的力学性质,进而使得粗粒花岗岩在高温高压条件下拥有更高的渗透性。这为干热岩地热开发过程中高效率、低成本以及大范围地建造人工储留层提供了良好的地质基础。

The real development of hot dry rock(HDR)geothermal is deep HDR geothermal.Because of different diagenesis environments,the mineral composition and micro-structure of deep granite are quite different from those of shallow granite.To reveal the real characteristics of deep granite and guide HDR geothermal development,the difference of thermal and mechanical properties between the granite in Luya Mountain,Shanxi Province,China(coarse-grained granite)and the granite in Shandong Province,China(fine-grained granite)under triaxial stress at high temperature(100-400℃)was studied.The results show that the thermal expansion coefficient of coarse-grained granite increases linearly with the increase of temperature,and the thermal expansion coefficient of coarse-grained granite is 1.52 times that of fine-grained granite on average,and the difference between them reaches the maximum at 400℃.The elastic modulus of coarse-grained granite increases first and then decreases with the increase of temperature,and its threshold temperature varying with temperature is 300℃.The elastic modulus of fine-grained granite is 1.4~2.6 times that of coarse-grained granite,and the difference increases with the increase of temperature and confining pressure.Micro-observation shows that the large number of preexisting fractures and extreme heterogeneity in coarse-grained granite lead to larger thermal deformation and more deteriorated mechanical properties of coarse-grained granite,and further make coarse-grained granite has higher permeability under high temperature and high pressure.This provides a good geological foundation for high efficiency,low cost and large-scale construction of artificial reservoirs in the process of HDR geothermal development.