Liquid nitrogen fracturing has emerged as a promising technique in fluid fracturing, providing significant advantages for the utilization and development of geothermal energy. Similarly to hydraulic fracturing in reservoirs, liquid nitrogen fracturing entails a common challenge of fluid–rock interaction, encompassing the permeation and diffusion processes of fluids within rock pores and fractures. Geomechanical analysis plays a crucial role in evaluating the transfer and diffusion capabilities of fluids within rocks, enabling the prediction of fracturing outcomes and fracture network development. This technique is particularly advantageous for facilitating heat exchange with hot dry rocks and inducing fractures within rock formations. The primary objective of this study is to examine the effects of liquid nitrogen fracturing on hot dry rocks, focusing specifically on granite specimens. The experimental design comprises two sets of granite samples to explore the impact of liquid nitrogen cooling cycles on the mode I fracture characteristics, acoustic emission features, and rock burst tendency of granite. By examining the mechanical properties, acoustic emission features, and rock burst tendencies under different cycling conditions, the effectiveness of liquid nitrogen fracturing technology is revealed. The results indicate that: (1) The ultimate load-bearing capacity of the samples gradually decreases with an increase in the number of cycling times. (2) The analysis of acoustic emission signals reveals a progressive increase in the cumulative energy of the samples with cycling times, indicating that cycling stimulates the release of stored energy within the samples. (3) After undergoing various cycling treatments, the granite surface becomes rougher, exhibiting increased porosity and notable mineral particle detachment. These results suggest that the cyclic application of high-temperature heating and liquid nitrogen cooling promotes the formation of internal fractures in granite. This phenomenon is believed to be influenced by the inherent heterogeneity and expansion–contraction of internal particles. Furthermore, a detailed analysis of the morphological sections provides insights into the structural changes induced by liquid nitrogen fracturing in granite samples.

Cryogenic stimulation using liquid nitrogen (LN2) has emerged as a promising alternative to conventional hydraulic fracturing for enhanced geothermal systems offering reduced environmental impact and improved stimulation efficiency. This study investigates the evolution of macro-mechanical properties and fracture structures in granite subjected to repeated high-temperature heating and LN2 cryogenic impact cycles—conditions simulating artificial thermal reservoir stimulation in hot dry rock environments. Standardized granite specimens were treated with varying thermal–cryogenic cycles followed by comprehensive characterization at multiple scales. Ultrasonic velocity measurements and spectral analyses were employed to assess internal damage and crack development induced by thermal–mechanical fatigue. Uniaxial compression tests were conducted to evaluate the degradation of mechanical parameters such as strength, stiffness, and failure mode. Furthermore, micro-computed tomography and three-dimensional laser profilometry techniques were integrated to quantify pore-fracture network evolution and surface morphology variations. The results demonstrate a progressive decline in mechanical integrity with increasing treatment cycles accompanied by enhanced connectivity and complexity of fracture networks. This study elucidates the coupled damage mechanisms induced by thermal shock and cryogenic contraction and provides experimental insights for optimizing LN2-based reservoir stimulation strategies in deep geothermal applications.