Experimental Study on Mode I Fracture Characteristics of Granite after Low Temperature Cooling with Liquid Nitrogen

Abstract

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.

Improvement of Thick Coal Seam Gas Drainage Efficiency Using Highly Pressurized Multidischarge CO2 Gas Fracturing Technique

“…Temperature has an influence on the expansion of coal seam fractures, and it can be considered that the temperature can also be taken into account in the expansion and development of coal seam fractures. Liquid nitrogen fracturing has become a promising fluid fracturing technology, which provides a significant advantage for the utilization and development of geothermal energy . In the future, we will further explore and improve the fracturing technology of high pressure multidischarge carbon dioxide gas, track the effect of coal seam permeability enhancement by establishing a long-term monitoring system, evaluate its sustainability, and conduct a comprehensive environmental impact assessment to ensure that the technology will not have a negative impact on groundwater, the surface environment, etc.…”

The application of evidence-entropy weight gray incidence theory on the risk assessment of rockburst intensity in the Daxiangling tunnel

“…The membership index g ij of the target i under index j is first determined, and the objective membership degree matrix G (g ij ) m×n is constructed; the normalized target membership matrix G (g ij ) m×n is obtained as (Wang et al, 2023b):…”

Experimental Study on Compaction Deformation and Gas Permeability Properties for Crushed Limestone

“…Meanwhile, it is an important direction for the development of clean energy in the future. , CBM is abundant in the mining goaf, and realizing its efficient exploitation and utilization is of great significance to optimize the energy structure . The gas permeability properties of coal and rock media in mining goaf are the basis for studying CBM enrichment and migration and the selection of surface drilling location. , The goaf formed by longwall mining can be divided sequentially into a caved zone, a fractured zone, and a continuous bending zone. , Notably, the crushed coal and rock in the caved zone is a triple pore structure with pores, fractures, and voids, which means that its internal pore space is much larger than the dual pore-fracture structure in the fractured zone and continuous bending zone . Crushed limestone is a common rock in the caved zone; it is of great theoretical and practical significance to master the evolution of its permeability properties during compaction for the efficient extraction of CBM in goaf.…”