Propagation of Cryogenic Thermal Fractures from Unconfined PMMA Boreholes

In cryogenic fracturing, a rock surface exposed to fluids undergoes large thermal gradient, and the resultant local tensile stress overcomes strength initiates fractures. This study investigates development of cracks generated from treatment borehole under no external confining on specimens. The experiments were performed transparent PMMA specimens observe fracture proliferation around boreholes. Liquid nitrogen was flowed through boreholes cool surface. results show that initial growth is characterized by abrupt starts stops, as propagates outward, appears more continuous. an early stage, horizontal/radial fractures vertical are defining patterns. Horizontal tend be separated specific exclusion distance (i.e., spacing between cracks). While distinct horizontal/vertical manifest themselves at resulting interactions curvatures can develop into complex shapes later stages. Cryogenic loading induces distinctively curved tendency curvature may prevent greater penetration. An increase in pressure during liquid flow, however, lessen tortuosity facilitate radial propagation. A high flow rate also advantageous they accelerate cooling