# Experimental Study on the Influence of Low Temperature on the Gas Permeability of Granite
###### Abstract
[24] employed NMR to analyze the pore size distribution characteristics of sandstone samples with initial damage. The results indicated that, during the first 20 freeze-thaw cycles, the number of micropores and mesopores increased. However, once the number of freeze-thaw cycles exceeded 20, subsequent changes in the pore size distribution were primarily dominated by the evolution of micropores. [PERSON] et al. [25] conducted a comparative study using NMR and three-dimensional X-ray micrography (3D-XRM) on granite, limestone, and sandstone samples before and after freeze-thaw exposure. The results revealed material-specific trends: mesopore content in granite, micropore content in limestone, and the emergence of macroporous structures all increased with repeated cycling. In sandstone, both micropores and mesopores showed an overall increase, highlighting the cumulative deterioration of internal pore structures. However, the operating temperature of underground LNG storage caverns--approximately \(-162\)\({}^{\circ}\)C--imposes more extreme cryogenic conditions than those typically considered in conventional low-temperature studies. This ultra-low-temperature environment is expected to have a more severe impact on the internal microstructure and mechanical integrity of surrounding rock masses. Most existing studies on rock degradation under cryogenic conditions have focused on moderate low-temperature ranges, creating a knowledge gap regarding the behavior of rocks under LNG-relevant temperatures. To address this, [PERSON] and [PERSON] [26] conducted uniaxial compression and tensile strength tests on granite and anddesite across a wide temperature range (\(-160\)\({}^{\circ}\)C to \(20\)\({}^{\circ}\)C), under both saturated and dry conditions. Their results revealed that the compressive and tensile strengths of both rock types increased as the temperature decreased, regardless of moisture content. [PERSON] et al. [7] investigated the fracture characteristics of saturated and dry granite within a temperature range of \(-165\)\({}^{\circ}\)C to \(25\)\({}^{\circ}\)C. Their study also introduced statistical models to describe the correlation between fracture energy and surface roughness at different temperatures. To date, most investigations into cryogenic damage in rocks have primarily focused on mechanical properties, while the gas permeability behavior of rocks under low-temperature conditions has received comparatively limited attention. However, rock permeability is a critical parameter that directly influences the stability and sealing performance of geological formations, particularly in the context of subsurface energy storage. It governs the ability of rocks to transmit fluids and, therefore, plays a decisive role in ensuring the safety and containment integrity of underground LNG storage systems. At the operating temperature of LNG storage caverns (approximately \(-162\)\({}^{\circ}\)C), significant alterations in the rock's internal microstructure may occur, potentially leading to complex changes in permeability. Given that permeability is strongly influenced by factors such as porosity, pore size distribution, and fracture connectivity, understanding its evolution under cryogenic conditions is essential. Investigating the permeability behavior of rocks at ultra-low temperatures is thus crucial for optimizing the design and ensuring the long-term safety and operational reliability of LNG storage caverns. It has been demonstrated that in underground coal gasification, a temperature of 1000 \({}^{\circ}\)C significantly influences the area within 0.5 m of the reactor chamber [27]. Similarly, the extreme low-temperature characteristics of liquefied natural gas (LNG), at approximately \(-162\)\({}^{\circ}\)C, exert a considerable influence on the surrounding reservoir rock, resulting in the formation of ice rings around the storage area [28].