| Compared to conventional coalbed methane reservoirs,The traditional transformation process is easy to cause blockage of coal holes and damage the reservoir structure.In order to increase the production of coalbed methane,it is necessary to unblock the blocked throat.The liquid flow cavitation technology is a physical stimulation method that utilizes the instantaneous high energy and high heat generated by cavitation bubble collapse to penetrate the coal seam pores and achieve the purpose of unblocking.This paper studies the liquid flow cavitation plugging and stimulation tool for coalbed methane,analyzes the structural characteristics of the coalbed methane plugging and stimulation tool through theoretical calculation,numerical simulation and experimental verification methods,and optimizes the structure to the research results.According to the difference between cavitation and evaporation and boiling,judging the conditions of cavitation effect,in order to understand the effect of cavitation effect on coal reservoir,establish a bubble dynamics model.The paper also analyzes the effects of viscosity,liquid compressibility,wall and pressure gradient on the cavitation bubble collapse to obtain cavitation bubble wall motion equation;impoves the permeability of coal-rock reservoirs and increases the cracks in coal seams to achieve production increasing through the implementation of liquid cavitation tools and supporting processes according to the characteristics of cavitation wave propagation in coal-rock reservoirs,coal reservoir and coalbed methane occurrence.This paper designs the stimulation tools of the jet,ring cavity and spoiler flow fields by analyzing the cavitation unblocking mechanism and calculate the corresponding dimensions establish the geometric model of the stimulation tool by CFD numerical simulation,analyzes the effects of structure,flow rate,cavity diameter ratio and nozzle diameter on cavitation performance,optimizes the structure of the plugging and stimulation tool.and finally verify the results by cavitation jet test bench and simulated reservoir environment.The results show that the three types of flow field structure have the highest efficiency of jet energy conversion.It is recommended to optimize the jet process parameters.It is recommended to use 30m/s asthe optimal flow rate for cavitation stimulation tool;the oscillation cavity is an important factor affecting cavitation performance.The analysis shows the cavitation performance when the aspect ratio is 0.6~0.7 greater than 0.5~0.6.The research results provide reference for the technology of CBM liquid cavitation stimulation. |
