Experimental investigation of water injection fracturing behavior and acoustic emission response of sandstone under true triaxial state

This research aims to delve deeply into the hydraulic fracturing (HF) behavior of sandstone under true triaxial stress conditions and its acoustic emission (AE) response characteristics in order to provide a theoretical foundation for optimizing HF designs and enhancing the efficiency of deep resource extraction. Through laboratory simulation experiments, we subjected white sandstone samples to HF using various water injection methods, employing AE monitoring technology to capture the fracturing activity within the rock in real-time. The study reveals that the technique of water injection significantly influences the fracturing behavior of the sandstone; a constant flow results in a continuous fracturing process, while staged cyclic and incremental water injection methods induce periodic variations in AE activity. AE waveform signals indicate that low-frequency and low-amplitude signals dominate during the injection process. Changes in the b-value reflect the development of internal fractures in the sandstone, offering precursory characteristics for fracturing. The rate of water injection plays a crucial role in fracture development, with staged cyclic injection showing the most significant fracture development. AE localization results correlate well with the fracture morphology, and the direction of fracture expansion exhibits anisotropy. The findings of this study provide significant theoretical insights into the AE responses during the water injection fracturing process in sandstone bodies and offer references for monitoring the scope of HF and assessing its effectiveness.