Permeability Evolution of Thermally Cracked Granite with Different Grain Sizes

The permeability of thermally cracked granites is crucial information for understanding and modeling a number of processes in the earth’s crust, such as folding, geothermal activity, magmatic intrusions, and nuclear waste disposal. Factors, including the coefficient of thermal expansion, elastic modulus, grain size, and bonding stress, have a significant impact on thermal cracking and induced permeability. We performed thermal cracking experiments on granite with different grain sizes to determine the effect of grain size on permeability. The results indicated that permeability increased with temperature up to 700 °C for all samples. The ratio of permeability at the target temperature to that at room temperature is an exponential function of temperature. Coarse-grained granite has a higher increase in permeability than fine-grained granite. A mathematical model was presented to explain the effect of grain size on thermal cracking and induced permeability. In addition, the model can also quantitatively describe the influence of the linear thermal expansion coefficient and elastic modulus of minerals on thermal cracking.