Laboratory Investigation on Cryogenic Fracturing of Coal Rocks: An Experimental Study in Kazakhstan

Cryogenic fracturing with liquid nitrogen (LN2) has been identified as a feasible and promising waterless fracturing method for coalbed methane extraction for its environmental safety and effectiveness. Though it performed well in certain field tests in the late twentieth century, the use of LN2 as the fracturing fluid is still largely unexplored. This research work examines the thermo-mechanical properties of coal specimens from the Karaganda basin in Kazakhstan. Coal specimens were subjected to LN2 treatment under varied lab-controlled conditions, such as the freezing time (FT) length and number of freezing-thawing cycles (FTC), both in dried and water-saturated conditions. SEM investigation for FTC and FT experiments for dried coal samples indicated that the LN2 freezing-thawing process can enhance the cryogenic fracture extent and the fracture interconnectivity. Moreover, uniaxial compressive tests indicated that compressive strength decreases beneficially with an increase in both the number of freezing-thawing cycles, while water-saturated experiments indicated substantial change after liquid nitrogen treatment compared to dried ones.