Experimental Study on Hydraulic Fracturing with Acoustic Emission under Tri-Axial Stress Conditions

Abstract

Abstract Hydraulic fracturing method is known as one of the most important stimulation methods, especially in unconventional gas and petroleum reservoirs. Acoustic emission (AE) is a popular technique to monitor the process of geomaterial failure during hydraulic fracturing. In the present paper, AE monitoring has been employed for a better understanding of the mechanism of crack and fracture generation in experimental hydraulic fracturing. Concrete blocks were subjected to true tri-axial stress conditions while AE was synchronously recorded during fluid injection. The experiments have been performed on the specimens under different loading stresses in order to investigate the effect of the applied pre-stress combinations. Based on the results, as the minimum horizontal stress increases, the fracturing pressure increases; moreover, when the maximum horizontal stress and vertical stress increase, the fracturing pressure shows an increasing and decreasing trend. Observed fractures align with the direction of maximum horizontal stress under anisotropic conditions, while isotropic stress conditions result in randomly oriented radial fractures. Analysis of AE parameters provides valuable insights, correlating with the physical fractures and cracks behavior and demonstrating the potential of AE monitoring as a predictive tool for hydraulic fracturing behavior.