Investigation on the Controlling Factors of Pressure Wave Propagation Behavior Induced by Pulsating Hydraulic Fracturing

Abstract

Summary Pulsating hydraulic fracturing (PHF) is a promising fracturing technology for unconventional reservoirs because it could improve the hydraulic fracturing efficiency through inducing the fatigue failure of reservoir rocks. Understanding of the pressure wave propagation behavior in wellbores and fractures plays an important role in PHF optimization. In this paper, a transient flow model (TFM) was used to describe the physical process of pressure wave propagation induced by PHF, and this model was solved by the method of characteristics (MOC). Combination of the TFM and MOC was validated with experimental data. The impacts of controlling factors on the pressure wave propagation behavior were fully discussed, and these factors include the frequency of input loading, an injection mode, an injection position, and friction. More than 10,000 sets of pressure wave propagation behaviors in different scenarios were simulated, and their differences were illustrated. In addition, the generation mechanisms of different pressure wave propagation behaviors were explained by the Fourier transform theory and the vibration theory. The important finding is that there is resonance phenomenon in the propagation of the pressure wave, and the resonance frequencies are almost equal to the natural frequencies of a fluid column. As a consequence of resonance phenomenon, the amplitudes of bottomhole pressure (BHP) and fracture tip pressure will increase sharply when the input loading frequency is close to the resonance frequency and less than 5 Hz; otherwise, the resonance phenomenon will disappear. Furthermore, an injection mode can alter the resonance frequency and the amplitude and frequency of the induced pressure wave. In addition, a friction effect can significantly decrease both the resonance frequency and the resonance amplitude. These findings indicate that the optimized input loading frequency should be close to the natural frequency of a fracturing fluid in a wellbore to enhance its BHP.

An advanced hydraulic fracturing technique: Pressure propagation and attenuation mechanism of step rectangular pulse hydraulic fracturing

“…It was concluded the abrupt pulse pressure could produce a better pressurization effect. Hou et al 33 used the transient flow model to describe the physical process of pressure wave propagation caused by pulse hydraulic fracturing. The effects of pulse frequency, injection mode, injection position, and friction are discussed.…”

Influence of Increasing Mean Stress on Fatigue Properties of Shale during Pulsating Hydraulic Fracturing

“…It is found that the form of the bottom hole pressure is controlled by the wellhead injection form in pulse hydraulic fracturing . A pulse flow at the wellhead can generate a cyclic load with the CAIMS at the bottom of the well.…”

“…It is found that the form of the bottom hole pressure is controlled by the wellhead injection form in pulse hydraulic fracturing. 15 A pulse flow at the wellhead can generate a cyclic load with the CAIMS at the bottom of the well. By contrast, a cyclic load with the CACMS at the bottom of the well is induced by the pulse pressure at the wellhead.…”

“…It has been proven that the PHF can fracture rock with a lower breakdown pressure compared with conventional hydraulic fracturing. − In addition, during PHF a more complex fracture network can be produced. − The form of pulse pressure exerted on rock determines the characteristics of rock failure and the fracture network. It has been demonstrated that there are two pulse pressure schemes applied on the rock according to their input pulse pressure schemes . One is constant amplitude and constant mean stress (CACMS) cyclic loading, and the other one is constant amplitude and increasing mean stress (CAIMS) cyclic loading.…”

“…It has been demonstrated that there are two pulse pressure schemes applied on the rock according to their input pulse pressure schemes. 15 One is constant amplitude and constant mean stress (CACMS) cyclic loading, and the other one is constant amplitude and increasing mean stress (CAIMS) cyclic loading.…”