Effects of High Temperature and Liquid Nitrogen Cooling: A Case Study of granite rocks from Kazakhstan

Cryogenic fracturing using liquid nitrogen (LN2) is a new geothermal well stimulation method to augment porosity, permeability, and overall contact area in Hot Dry Rock (HDR) reservoirs in an environmentally acceptable way, without potential surface or groundwater contamination, formation damage, and huge water consumption. Procedures representing different exposure times and frequencies were compared by investigating the degree of rock integrity damage created. Granite rocks equilibrated at different elevated temperatures from 200oC to 500oC were immersed in LN2 for different freezing times (FT) and a variable number of freezing-thawing cycles (FTC). Rock strength was measured in compression tests. Scanning electron microscopy (SEM) was used to confirm the extent of visible damage and catalog the fracture evolution of our granite specimens. Two different granite rocks were studied: Zhylgyz (sample 1) and Sayac (sample 2). The experiments document mechanical rock damage by thermal shock and the degree of thermo-fracturing rises with temperature difference and time of LN2 treatment in both freezing time and freezing-thawing cycle methods.