Investigation of Physical and Mechanical Properties of Hot Dry Rock as a Geothermal Energy Source After LN₂ Cooling

To investigate the impact of liquid nitrogen (LN₂) as a stimulation method to increase reservoir contact with hot dry rock, we carried out a sequence of physical and mechanical examinations on Kazakhstani granite specimens. Granite samples were gradually heated to desired temperatures ranging from 50 °C to 500 °C. Subsequently, rapid cooling was implemented using two different coolants: water, and LN₂. Following the thermal treatments, we conducted tests to evaluate both the physical and mechanical properties of the samples. Based on the experimental findings, the permeability of the heated granite samples notably rises following LN₂-cooling, accompanied by reductions in P- wave velocity, and strength, as evidence of internal thermal shock fracturing. As the initial temperature increases, these alterations in properties become more pronounced. In comparison between water-cooling and LN₂-cooling, the latter leads to more significant changes in both physical and mechanical properties across all target temperatures. This suggests that LN₂cooling can yield more effective stimulation of hot dry rocks compared to the water-cooling method.