We study damage induced by low temperature variations in granite samples given their role in shallow geological reservoirs. We consider two thermal treatments, slow cooling and thermal shock, and implement a multi-geophysical approach to characterize the induced micro-scale damage. The methodology consists in monitoring elastic wave velocity and thermal conductivity as well as describing the damage by the way of Hg-porosity measurements and microscopic observations. To discuss the reproducibility of the induced damage, the same thermal protocol is performed on five samples. Our first results indicate that the thermal shock leads to a more pronounced damage. This is interpreted to be due to a larger variety of nucleated intragranular and intergranular cracks as observed by SEM and optic microscope. Yet, this more significant damage does not appear reproducible from one sample to another compared to the damage introduced by slow cooling. According to this first result, thereby, we propose a timely monitoring of elastic wave velocity, conductivity and Hg-porosity. It appears that the damage introduced by the slow cooling, unlike the thermal shock, does not present a long persistence. Indeed, after 15 days, the different properties had returned to their initial state. A time-dependence mechanism is proposed to discuss this observed process.

中文翻译：

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用于表征花岗岩中热致裂纹的多地球物理方法：再现性和持续性的讨论

鉴于花岗岩样品在浅层地质储层中的作用，我们研究了它们由低温变化引起的损伤。我们考虑两种热处理，缓慢冷却和热冲击，并实施多地球物理方法来表征诱导的微尺度损伤。该方法包括监测弹性波速度和热导率，以及通过汞孔隙度测量和显微观察来描述损伤。为了讨论诱导损伤的再现性，对五个样品执行相同的热协议。我们的第一个结果表明热冲击会导致更明显的损坏。这被解释为由于通过 SEM 和光学显微镜观察到的更多种类的晶内和晶间裂纹。然而，与缓慢冷却造成的损坏相比，这种更显着的损坏似乎无法从一个样品复制到另一个样品。因此，根据第一个结果，我们建议及时监测弹性波速度、电导率和汞孔隙度。与热冲击不同，缓慢冷却引入的损坏似乎不会持续很长时间。事实上，15 天后，不同的属性已经恢复到它们的初始状态。提出了一种时间依赖机制来讨论这个观察到的过程。不呈现长久的持久性。事实上，15 天后，不同的属性已经恢复到它们的初始状态。提出了一种时间依赖机制来讨论这个观察到的过程。不呈现长久的持久性。事实上，15 天后，不同的属性已经恢复到初始状态。提出了一种时间依赖机制来讨论这个观察到的过程。