Dynamic stress response and fatigue characteristics of tight sandstone reservoirs with pulsating hydraulic fracturing

Abstract

During pulsating hydraulic fracturing (PHF), the reservoir generates dynamic stress response and fatigue damage under the excitation of fluctuating fluid pressure. However, it remains to be determined which is the primary factor affecting fracturing effectiveness, particularly for tight sandstone reservoirs. Identifying the critical factors that govern the effectiveness can help optimize the fracturing scheme and increase production. The present study employed laboratory experiments and numerical simulations to investigate its mechanism. Specifically, the rock triaxial loading test system was utilized to conduct the PHF experiments. It was analyzed that the effect of maximum pressure and frequency on breakdown pressure, acoustic emission signals, and fracture morphology. Subsequently, a three-dimensional numerical simulation model of dynamic stress response was established using ABAQUS. The influence of the maximum pressure and frequency on the stress response amplitude was also discussed. The experimental results revealed that PHF can cause fatigue damage to the specimens. Interestingly, compared to conventional hydraulic fracturing (CHF), PHF can reduce the breakdown pressure. Additionally, it is beneficial to reduce the fatigue life by increasing the maximum pressure or decreasing the frequency. From the simulation results, enhancing the maximum pressure can notably improve the stress response amplitude. However, in the low-frequency range, the frequency variation has a minor impact on the amplitude. To conclude, the fracturing effect primarily relies on the fatigue damage effect rather than the dynamic stress in the low-frequency range. The results are significant for comprehending the PHF mechanism and determining parameters in engineering applications.