Study of Pulse Wave Propagation and Attenuation Mechanism in Shale Reservoirs During Pulse Hydraulic Fracturing

Abstract

Hydraulic fracturing (HF) is indispensable in shale gas, but there are also problems existed in high ratio of energy consumption and low ratio of energy utilization. Based on hydraulic fracturing and pulsating jet, pulse hydraulic fracturing (PHF) has been widely used and achieved good results in the coal-bed methane. This paper attempts to study the mechanism of pulse wave propagation and attenuation during PHF in shale reservoirs, which provides theoretical support for application. On the basis of the motion equation and continuity equation, the two-dimensional propagation and attenuation equation with damping and fissure width during PHF is established and fracture network is simulated based on DFN discrete random model. The mathematical and physical model is verified by laboratory experiment The study of PHF superiority, PHF waveform effect, PHF propagation and attenuation characters are also performed. Results indicate that PHF propagation has two stages: The first is the pressure fluctuation is sharp in the process of the initial fracturing. The second is a stable state is appeared after a period of time. Compared with HF, PHF can pressurize obviously the pressure gradient of pulse waveform, which is an important parameter of affecting pulse pressure: the greater pressure gradient, the more obvious water hammer and supercharging effect. In the process of PHF propagation, pressure distribution complicates under the supercharging. Pressure wave has different attenuation characteristics in two steps. These research results will provide guidance for optimizing technical parameters for using PHF technology in shale reservoirs.