Study of Rock Crack Extension under Liquid Nitrogen Low-Temperature Fracturing

Shale gas is a promising new energy source stored in shale. This research aims to study the laws of rock crack initiation and propagation under low-temperature fracturing liquid nitrogen, explore influencing factors shale reservoir effect, identify method that achieves best effect obtains highest economic benefits. Herein, visualized physical experiment nitrogen carried out, fracture process numerical model cold shock simulated analyze homogeneity on propagation. The results show two different development modes could be observed field test. first one was horizontal plane radial caused by longitudinal thermal shrinkage, other vertical tensile circumferential shrinkage. A certain interval length frequently found between cracks. specimens with homogenization degrees basically distributed direction perpendicular contact surface. When were m = 2 5, surface rough microfracture disordered dotted around tip. ≥ 10, damage tip did not appear, close obtained from using homogeneous materials. Finally, this work simulates circular hole shock, analyzes influences heat transfer coefficient, situ stress parameters temperature, minimum principal distribution, propagation, discusses optimal improve coefficient. increasing coefficient can increase value influence range boundary, making more prone cracking resulting greater better effect. lateral affects cracks, depths cracks deeper larger stress.