Analysis of impact pressure, rock-breaking effect, and ground vibration induced by the disposable CO2 fracturing tube

Abstract

The technology of expansion fracturing with liquid CO2 (EFLCO2) has attracted increasing attention due to reduced vibration and damage. The disposable fracturing tube has been developed and is gradually replacing the Cardox tube. However, there is a lack of impact pressure testing of disposable tubes under real working conditions, selection of gas explosion design parameters, and systematic analysis of blasting vibration. This limitation has constrained the widespread application of disposable fracturing tubes in engineering. A joint monitoring of the pressure-time curves in the disposable tubes and boreholes was conducted. The rock-breaking effect of varying hole spacing parameters in the EFLCO2 design was analyzed, and a systematic study was carried out on the vibration peak value, frequency, and energy characteristics. The results show that (1) the pressure distribution characteristics, stress peak value, and duration in the disposable tubes are different from those of Cardox tubes, which show multi-peak distribution, low-pressure peak value, and short duration. The correlation between the pressure in the disposable tube, filling pressure, and liquid CO2 weight is established, and a theoretical calculation method for the borehole wall pressure is proposed; (2) The hole spacing in rocks of different hardness is suggested; and (3) At the same scale distance, the peak particle velocity (PPV) caused by EFLCO2 (PPVCO2) is significantly smaller than that caused by blasting (PPVexplosive). The ratio of PPVexplosive to PPVCO2 is a power function related to scale distance, and a distance-related zonality exist in this relationship. The frequency composition of the vibration signal caused by EFLCO2 is relatively simple with a narrow frequency band. Its PPV and energy are mainly concentrated in the low-frequency band. This research contributes to the optimization of disposable fracturing tubes, gas explosion design, and vibration hazard control.

Keywords

• Disposable tube
• Liquid CO2
• Impact pressure
• Hole spacing
• Vibration effect
• Cardox tube