Study on Mechanism of Strength Deterioration of Rock-Like Specimen and Fracture Damage Deterioration Model Under Pulse Hydraulic Fracturing

Pulse hydraulic fracturing is an effective fracturing stimulation technology, which can reduce rock breakdown pressure and improve fracturing effects. Under pulse hydraulic loading, fatigue damage occurs in the rock, and the rock strength gradually deteriorates. However, the characteristics of rock strength deterioration and rock fracture mechanisms under different pulse hydraulic pressures are not clear, and the fracture model induced by strength deterioration has not been well established. In this study, strength deterioration tests are carried out under different pulse hydraulic pressures, and tensile strength deterioration curves are obtained. We introduce the strength deterioration curve in the continuous discontinuous element method (CDEM) to establish the fracture damage deterioration model of rocks, and implement crack propagation using the improved cohesion zone model. The validity of the fracture damage deterioration model is verified by comparison with the test results. During pulse hydraulic loading, the hydraulic pressure of pulse loading can influence fatigue tensile strength and hydraulic fracture propagation behaviors. With the decrease of pulse loading stress ratio, the fatigue tensile strength gradually decreases, resulting in more fractures in the specimen. Under different pulse loading stress ratios, with the increase of pulse loading numbers, the damage tensile strength of the specimen decreases gradually. When the pulse loading stress ratio is low, the degree of damage to the tensile strength decreases significantly, which easily induces rock failure and increases the fracturing effect.

Automated summary

Pulse hydraulic fracturing is an effective technique for rock fracturing and stimulation, but the characteristics of rock strength deterioration and fracture mechanisms under different pulse hydraulic pressures are not well understood. This study investigates the strength deterioration of rocks under different pulse hydraulic pressures and establishes a fracture damage deterioration model, which is validated by experimental results.