不同热处理作用下花岗岩纵波波速和导热能力的演化规律分析

Evolutions of P-wave velocity and thermal conductivity of granite under different thermal treatments

在地热能源开采过程中,温度对高温岩石的物理特性有着显著的影响,尤其是高温花岗岩遇水冷却后导热特性会发生很大的变化。为进一步研究温度和冷却方式对高温花岗岩物理特性的影响,开展高温花岗岩自然冷却和遇水冷却试验,通过对其质量、体积、密度和波速等常规物理特性以及导热特性的测试,对比分析2种冷却方式下的物理参数变化规律。结果表明:质量损失率、体积增加率、密度变化率和波速衰减率随温度的升高呈指数型增加,当温度T=450℃时,花岗岩的物理特性变化率显著增加。遇水冷却能够增大花岗岩微裂纹密度,导致其物理特性进一步变化。热处理后花岗岩的导热系数随温度(25℃~1 050℃)升高呈非线性降低,由3.41 W/(m·K)降至0.96 W/(m·K),降低了72.85%。热处理后花岗岩的导热系数与其质量损伤率、体积增加率和波速衰减率成负相关,可以用指数函数来表示。对比各物理参数的改性系数发现,在敏感性方面:纵波波速>导热系数>密度,因此纵波波速可以优先作为衡量花岗岩热损伤的指标参数。

In the exploitation process of geothermal energy,the temperature has a significant impact on the physical properties of dry hot rock,especially the thermal conductivity of high-temperature granite after water cooling. In order to investigate the influence of the temperature and the cooling mode on the physical properties of hightemperature granite,the air-cooling and water-cooling experiments of high-temperature granite are carried out in this paper. Through investigating the conventional physical properties such as mass,volume,density and P-wave velocity as well as the thermal conductivity,the change rules of the parameters by the two cooling methods are compared and analyzed. The results show that the mass loss rate,volume increase rate,density change rate and P-wave velocity decay rate increase exponentially with the temperature. When T = 450 ℃,the change rate of granite physical properties increases significantly. Water-cooling increases the density of micro-cracks in granite,which causes further changes in the physical properties of granite. After thermal treatment,the thermal conductivity of granite decreases non-linearly by 72.85% from 3.41 W/(m·K) to 0.96 W/(m·K) with increasing the temperature from 25 ℃ to 1 050 ℃. The thermal conductivity of granite after thermal treatment is inversely related to the mass damage rate,volume increase rate and P-wave velocity decay rate in an exponential form. Comparing the physical parameters, it is found that P-wave velocity is most sensitive to the temperature, followed by the thermal conductivity and the density. Therefore,P-wave velocity can be used preferentially as an index parameter to measure the thermal damage of granite.