Integrated Pressure Build-Up and Stress Response to Hydraulic Stimulation: A Laboratory Method to Reflect Fluid–Structure Interaction

Varied stress field is a time-response to fluid–structure interaction and the relationship between induced stress and fluid pressure is the key to clarify damage evolution in hydraulic stimulation. Here, we introduced the stress sensor and acoustic emission monitoring into hydraulic fracturing. Constant and fluctuant fluid–structure interaction with different duration and magnitudes of fluid pressure were conducted in hydraulic stimulation. By defining fluid pressure-induced stress sensitivity coefficient, the response of induced stress to fluid pressure was recognized: induced stress is subjected to fluid pressure and interaction duration, the fluctuant fluid pressure relieves stress diffusion. With the increase of interaction duration, and the induced stress and the crack propagation pressure increase, while the peak fluid pressure decreases. Induced stress and the normalized value of the depressurization rate can synergistically characterize the fracturing crack width, and the crack width decreases with the increase of induced stress. Induced stress of a small crack is greater than that of a large crack, and microdamage has a profound impact on the induced stress. With the increase of induced stress, the stress intensity factor of tensile crack decreases, while that of shear crack increases. The increase of induced stress accelerates the generation of shear crack. The comprehensive analysis system between induced stress and fluid pressure was proposed to improve the technological parameters of hydraulic fracturing and enhance the accuracy of evaluation of fracturing accomplishment, which is of great significance for promoting unconventional reservoir exploitation.