Study on Fluid Pressure in Tubing, Dynamic Stress in Reservoir, and Fracture Propagation Morphology During Variable‐Rate Hydraulic Fracturing

Abstract

Hydraulic fracturing represents an effective stimulation approach for exploiting low‐permeability oil and gas reservoirs, which is essential for boosting well productivity. However, conventional constant‐rate hydraulic fracturing (CRHF) is plagued by issues such as high operation pressure, difficulty in forming complex fractures, and induced seismicity. Recently, variable‐rate hydraulic fracturing (VRHF) has attracted attention, with preliminary laboratory experiments and field tests demonstrating its potential to mitigate these challenges. Nevertheless, the stimulation mechanism of VRHF remains unclear. Compared with CRHF, VRHF introduces a series of dynamic issues, rendering traditional static fracturing theories inadequate. This paper conducts a systematic analysis of the following aspects during the operation of VRHF, including the research on fluid pressure propagation in the tubing, reservoir stress distribution, reservoir fatigue damage, fracture initiation and propagation, and induced seismicity. The results indicate that VRHF can induce unsteady flow in the tubing, thereby generating fluctuating fluid pressure near the bottom‐hole reservoir. Dynamic stress is generated in the reservoir under the action of fluctuating fluid pressure and propagates as stress waves. Furthermore, fluctuating fluid pressure can induce fatigue damage in the reservoir. These effects are beneficial for reducing breakdown pressure, modifying fracture propagation behavior, and mitigating the magnitude of induced seismicity. For future research, it is imperative to develop a coupled simulation model that integrates tubing fluid flow and reservoir fracture propagation, together with seismic monitoring during fracturing operations. It is highly significant for field operations to optimize the operational parameters using the aforementioned model, with the objective of forming a complex fracture network under the constraints of maximum operating pressure and induced seismicity magnitude.