Generation and propagation characteristics of fluctuation pressure in hydraulic fracturing with unstable fluid-injection

Abstract

Different from the stable injection mode of conventional hydraulic fracturing, unstable fluid-injection can bring significant dynamic effect by using variable injection flow rate, which is beneficial to improve the fracturing effect. Obviously, the propagation process of fracturing fluid along the pipe string is crucial. In this paper, the fluid transient dynamics model in the pipe string was established, considering the boundary conditions of variable injection flow rate and reservoir seepage, and the unsteady friction was also taken into account. The above model was solved by characteristics and finite difference method respectively. Furthermore, the influences of geological parameters and fluid-injection schemes on fluctuating pressure were also analyzed. The results show that unstable fluid-injection can cause noticeable fluctuation of fracturing fluid in the pipe string. Simultaneously, there is attenuation during the propagation of pressure fluctuation. The variation frequency of unstable fluid-injection and well depth have significant effects on pressure fluctuation amplitude at the bottom of the well. This research is conducive to understanding the mechanism of unstable fluid-injection hydraulic fracturing and providing guidance for the design of fluid-injection scheme.

Keywords

hydraulic fracturing / unstable injection / transient flow / fluctuation pressure / seepage

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