Characterization method and parameter analysis of multi-hole liquid CO2 flash boiling jet morphology during coal seam drilling process
摘要
The application of hydraulic technology can markedly enhance the efficiency of coalbed methane extraction. Nevertheless, when it comes to enhancing permeability in deep, soft coal seams, existing hydraulic techniques often encounter challenges such as water locking, hole collapse, and drill bit sticking. Anhydrous technology offers a robust solution to these issues by eliminating the adverse effects of water on soft coal seams at the source. Due to its unique physical properties, CO2 has developed anhydrous technologies such as CO2 jet impact rock breaking and phase change induced fracturing blasting. CO2 flash boiling jet, a novel jet technology, demonstrates potential in achieving optimal matching between impact force and working area in coal seam drilling applications, attributed to its features of phase change impact, extensive working area, and balanced force distribution. The expansion and collapse characteristics of multi-hole liquid CO2 flash boiling jet are pivotal in determining its impact effectiveness. However, the traditional jet characterization method is inadequate for capturing the intricate flow field structure of multi-hole flash boiling jets. By using a unified fitting method and characteristic parameters, it is possible to accurately compare the flow field characteristics of different jets, clarify the impact mechanism of each jet parameter on the flow field, and provide an effective characterization method for precise control of jet parameters to improve drilling capacity. A characterization method based on boundary fitting is developed to analyze the flow field morphology of multi-hole liquid CO2 flash boiling jets through visualization experiments. The jet flow field images were collected, and image processing techniques were used to extract boundary point information. A nonlinear fitting function was employed to fit the boundary points, revealing the limitations of the boundary fitting method. Two new methods for fitting the boundary points b