The pulsating hydraulic fracturing (PHF) technology generates a pulse pressure wave at a wellhead and then propagates this pulse pressure wave to the wellbore end to fracture the rock. Compared with the conventional hydraulic fracturing (CHF), PHF can induce more complex hydraulic fracture network with lower breakdown pressure. However, the difference of bottom hole pressure (BHP) acting modes between CHF and PHF is still not clear. In this study, the BHP of CHF was calculated by the conventional-BHP model, while the BHP for PHF was obtained by the transient flow model and the method of characteristic. The BHPs during the PHF for different input frequencies ranging from 0.01 Hz to 20 Hz were calculated. In addition, the difference of BHP acting modes between the CHF and PHF was analyzed and illustrated. Results show that the BHP of the CHF is a constant pressure that smaller than the wellhead pressure. In contrast, the BHP of PHF is a pulse pressure with the same frequency as the input frequency when the input frequency is smaller than 10 Hz. Moreover, the amplitudes of BHPs for different input frequencies fluctuate with the input frequencies, and there are 17 pressure peaks for input frequencies ranging from 0.01 Hz to 20 Hz. According to the Vibration Theory, these 17 pressure peaks are induced by the resonance phenomenon and the corresponding frequencies are resonance frequencies. By optimizing the input frequency, a pulse BHP with an amplitude that is two times of the input amplitude at the wellhead can be obtained. These results provide guidance for the design and optimization of PHF construction parameters.

1. Introduction

Hydraulic fracturing is a widely applied technology for permeability enhancement in unconventional reservoirs, such as shale gas, tight oil and CBM (Dong et al., 2019; Karacan et al., 2011). Pulsating hydraulic fracturing (PHF) technology is a novel hydraulic fracturing technology, which has been proposed and proved efficient in CBM in recent years (Li et al., 2011; Lin et al., 2012; Wu et al., 2016; Ni et al., 2018). During the PHF, a fracturing fluid is injected into the reservoir with a certain frequency to generate a pulse pressure wave loading on the rock. Under the action of this pulse pressure wave, the rock will undergo fatigue damage, which results in a complex hydraulic fracture network (Wang et al., 2015; Xu et al., 2017; Ni et al., 2018).

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