Experimental Evaluation of Liquid Nitrogen Fracturing on the Coal Rocks in Karaganda Basin, Kazakhstan

This work examined the efficacy of liquid nitrogen (LN2) both in coal fracturing, focusing on two different processes: freezing time (FT) and freezing-thawing cycle (FTC), for both dry and water-saturated specimens. Uniaxial compressive strength (UCS) with acoustic emission measurements, hardness, and modulus measurements by nanoindentation, and scanning electron microscope (SEM) imaging were conducted to comparatively analyze the cryogenic treatment efficacy of coal rocks. The outcomes indicated that in all freezing-thawing processes, water-saturated specimens have lower UCS values compared to dry ones. On the other hand, in freezing time process, water-saturated experiments have larger UCS values compared to dry ones. Moreover, it is noticed that FT experiments have greater UCS values than FTC experiments in both dry and water-saturated experiments. The hardness and reduced modulus change augment for both water-saturated and dry specimens, but in water-saturated ones, there is a sharp upward trend indicating that hardness decreases more as LN2 treatment increases. From SEM observation, it is noticed that new fractures were created, and sections of preexisting crevices expand creating fracture networks. Due to the frost force resulting from LN2 treatment, the consolidation forces among coal particles are compromised, thus creating new fractures.

Automated summary

This study investigated the effectiveness of liquid nitrogen (LN2) in fracturing coal rocks through two different processes: freezing time and freezing-thawing cycle. It was found that water-saturated specimens had lower compressive strength than dry specimens in all freezing-thawing processes. However, in the freezing time process, water-saturated experiments showed higher compressive strength compared to dry experiments. SEM observation revealed the formation of new fractures and expansion of preexisting crevices, creating fracture networks. The consolidation forces among coal particles were compromised by the frost force resulting from LN2 treatment, leading to the formation of new fractures.