Pulse injection simulation based on the coupling of transient flow in tubing and fracture propagation in reservoirs

Abstract Pulse injection can reduce the maximum operating pressure at the wellhead, which is conducive to solving the operational difficulties caused by the high breakdown pressure. The new injection mode causes a transient fluid flow in the tubing, and it interacts with the initiation and propagation of hydraulic fractures. However, there is still a lack of theoretical models to consider the above factors so that its mechanism cannot be explained. In this study, the transient flow model in the tubing was first established. Subsequently, the fracture propagation model was completed based on particle flow code (PFC). Moreover, the transient flow model was embedded into the PFC simulation software via its code script FISH. Finally, their coupled simulation model was established. Based on this model, the effects of injection flow rates on the fluid pressure in the tubing and the initiation and propagation of hydraulic fractures were discussed. Furthermore, the influence of parameters in the pulse injection scheme on the maximum wellhead pressure was studied by the orthogonal design method. The results show that with the increase of the injection flow rate, the fluid pressurization rate in the tubing and the fracture propagation rate both raise, which also causes a significant increase of the maximum wellhead pressure. Compared with a stable injection mode, pulse injection can evidently reduce the maximum wellhead pressure. The influence degree of each parameter on the maximum wellhead pressure in the pulse scheme is as follows: t2 > Δq > Δt4 > Δt5 > Δt3. The research results of this paper have guiding significance for the engineering application and parameter design of pulse injection hydraulic fracturing.