Discrete element simulation model of pulsating hydraulic fracturing considering fatigue damage

Pulsating hydraulic fracturing (PHF) is an effective stimulation technology that has attracted attention in the past years. To obtain the ideal fracturing effect, it is necessary to understand the response characteristics of the rock under pulsating pressure. However, the current mathematical models are unable to simulate the fatigue characteristics of the reservoir and its complex internal fracture propagation law during PHF. This study created a fluid-structure coupling hydraulic fracturing simulation model with consideration of the fatigue damage by particle flow code (PFC). Fatigue degradation was implemented by the proposed parallel-bonded corrosion model. Additionally, it was embedded into PFC via code script FISH. Based on the results of the simulation model, the fracturing effects of PHF and conventional hydraulic fracturing (CHF) were compared. Furthermore, the influence of maximum and minimum pressure in the pulsating injection scheme on breakdown pressure and hydraulic fractures propagation morphology was also discussed. The results indicate that in comparison to CHF, PHF can effectively reduce the breakdown pressure, activate the natural fractures in the reservoir and increase the complexity of the hydraulic fractures. The pulsating pressure causes the particle skeleton stress in the reservoir and the fluid pressure in the hydraulic fractures to fluctuate, while the fluctuation amplitude gradually decreases with the increase of the distance from the injection hole. With the decline of the maximum pressure or the increase of the minimum pressure, the fatigue life of the reservoir increases. Simultaneously, reducing the maximum pressure and the minimum pressure is contributive to activating more natural fractures. The obtained results are helpful to understand the formation mechanism of complex fractures in the reservoir during PHF and provide guidance for its engineering applications.

Automated summary

This study created a fluid-structure coupling hydraulic fracturing simulation model with consideration of fatigue damage to investigate the effects of pulsating pressure on rock fracturing. The results indicate that compared to conventional hydraulic fracturing, pulsating pressure can reduce the breakdown pressure, activate natural fractures, and increase the complexity of hydraulic fractures.