Work

Influence of liquid CO2 phase transition blasting on hydraulic fracturing in combined fracturing conditions

Year: 2025

Type: article

Abstract: Enhancing the permeability of coal seams is crucial for improving coalbed methane extraction. To better understand the effects of liquid CO2 phase change blasting on hydraulic fracturing within gas-liquid combined permeability enhancement technology, a multifunctional fracturing tube was developed, capable of achieving combined gas-liquid fracturing. Experiments were conducted on dense artificial samples under simulated in-situ stress conditions. The results indicate that the fracture morphology and distribution induced by liquid CO2 phase change blasting are strongly influenced by the number and arrangement of fracture holes at the energy release end of the multifunctional fracturing tube. Specifically, a single-hole energy release structure promotes the formation of directional long fractures. The hydraulic fracturing process can be divided into four distinct stages: filling, cyclic energy storage and fracturing, drainage, and pump stopping. Notably, the initiation and propagation of hydraulic fractures primarily occur during the cyclic energy storage and fracturing stage, where a strong correlation between injection pressure and acoustic emission (AE) energy signals was observed. The relationship between breakdown pressure and in-situ stress shows that a reduction in maximum principal stress () increases the sample's breakdown pressure, while intermediate () and minimum () principal stresses exhibit the opposite effect. After liquid CO2 phase change blasting, the influence of blasting-induced fractures on hydraulic fractures is reflected in three key aspects: shortening the duration of the cyclic energy storage and fracturing stage, reducing breakdown pressure, and altering the fracture propagation direction. These findings hold significant implications for enhancing coalbed methane extraction and optimizing construction parameters in coal seam gas-liquid combined permeability enhancement technology.

Source: Physics of Fluids

DOI: 10.1063/5.0256807