Effects of hydrothermal treatment on dynamic properties of granite containing single fissure subject to impact loading

The largest potential of geothermal energy lies in the hot granitic basement rocks with low permeability deep in the earth. Deep granitic rocks are usually exposed to the coupled water and thermal environment over a long period of time, as well as dynamic disturbance caused by drilling and excavation. Understanding the influence of low temperature water on rock is of great significance for effectively developing complex fracture network and improving the permeability of energy reservoirs. To investigate the dynamic characteristics of granite under the influence of water and temperature, impact tests were carried out on granite samples soaked in water at temperatures vary from 25 to 150 degrees C. The hydrothermal effects on dynamic mechanical characteristics of specimens were investigated by using a split Hopkinson pressure bar system. In addition, the porosity distribution and hydrothermal damage were studied and discussed. The results show that the dynamic compressive strength and elastic modulus are negatively correlated to water temperatures. The mechanical properties of the specimens are obviously weakened by thermal water immersion, and the weakening effect is very sensitive to water temperature. Strain rate improves the mechanical strength of granite. The porosity distribution of nuclear magnetic resonance shows that the number and size of pores and microcracks increase with the rising temperature. The T-2 spectrum after loading has a wider distribution range and higher spectrum peaks than that before loading. Hydration can cause new damage in the granite, and the increase in water temperature will aggravate the hydrothermal damage.

Automated summary

The research shows that the dynamic compressive strength and elastic modulus of granite are negatively correlated with water temperature, while strain rate can enhance the mechanical strength. The number and size of pores and microcracks in granite increase with rising temperature, and higher water temperatures exacerbate hydrothermal damage.