Pulse effects on proppant migration and dune shape in vertical fracture applied in coalbed methane mining engineering during the pulse hydraulic fracturing

Proppant migration plays a very important role in the pulse hydraulic fracturing (PHF). However, it is unclear that the pulse effect mechanism and regularity on the proppant migration in fracture. This study combined PHF and proppant migration for the first time to reveal the pulse effects on the migration and distribution of proppant. This work was conducted based on the Eulerian-Eulerian two-phase model and computational fluid dynamics method. Firstly, the simulations were validated by two typical experiments. Then, the pulse injections of slurry were carried out in a vertical fracture. Last, the influences of pulse shape, amplitude and period were discussed in detail. The results show that the square pulse can decrease the dune deposition height in the near region of fracture, and the decrease has a positive correlation with the pulse period, where the maximum decrease is up to 22.6%. It's found that the square pulse can increase the dune deposition height in the middle and far regions of fracture, and the increments have positive correlation with the pulse period, where the maximum increments are 47.7% and 61.5%, respectively. The present results indicate that the square pulse injection can extend the migration range of proppant. The extended-range effect has a positive association with the pulse period. Besides, results show that the extended-range effect is apparent only when the pulse amplitude is larger than 0.3 m/s. Compared to the sine pulse injection, the square pulse injection provides better extended-range effect. The present findings can provide valuable theoretical guidance for the PHF design and efficient exploitation of coalbed methane.