Experimental and numerical investigations on hydraulic fracture growth using rock-like resin material containing an injecting inner pre-crack

Abstract

A new transparent resin material with a compression-tension strength ratio of up to 6.6 at −15∼-10 °C has been developed. It possesses more brittle fracture properties than before and can competently simulate many kinds of engineering rocks. The fabrication demands strict temperature control and treatments. Specimens are inventively made with a hollow injecting inner pre-crack. Based on self-designed water injection devices and low-temperature loading equipment, uniaxial and biaxial hydraulic fracturing experiments are carried out under fixed water pressures. The specimens' uniaxial hydraulic failure process can be separated into four stages. At each stage, the variation of water injection is analysed. For all experiments, both crack initiation stress and peak strength have declined significantly, by more than 80% and 70% compared with dry specimens. The evolution of wrapping wing cracks and fin-like cracks in biaxial experiments has rarely been reported before. Moreover, numerical verification is conducted by FLAC3D. A novel fluid-solid coupled model has been developed that takes into account both the pre-peak damage and post-peak sharp degeneration. The principles are dependent on the element's failure type, i.e., tensile failure, shear failure, or a combination of the two. The mechanical parameters and permeability coefficient of damaged elements are redefined. The simulation results match well with experiments, demonstrating the feasibility of this method. Finally, the proposed model is applied to explore the hydraulic failure of the specimen under triaxial compression with fixed stress. The impact of injecting pre-crack on hydraulic fracture growth is illustrated.