Performance Analysis And Optimization Of Hydraulic Cavitation Tool For Increasing Coalbed Methane Production

Due to the characteristics of multiple pores and low permeability of coal reservoirs,traditional stimulation measures,such as hydraulic fracturing,have the problems of large coal damage,high pollution,and poor adaptability.The hydraulic cavitation jet technology can generate a large amount of energy by inducing cavitation collapse,including mechanical vibration and thermal energy.The coal seam is deformed alternately to achieve the effect of tearing the coal seam,thereby increasing the porosity,and at the same time reducing the adsorption capacity of the coal seam gas on the coal body,so as to achieve the purpose of increasing the production of coal bed methaneIn this paper,the cavitation tool for improving coalbed methane recovery is taken as the research object First,based on hydroacoustics and bubble dynamics,the kinetic characteristics of cavitation bubbles in the process of birth,growth and compression are analyzed.The occurrence characteristics of coalbed methane in the reservoir are analyzed,and the models of cavitation initiation and collapse suitable for coal seam pores and the wave equation of pressure wave propagation are established.Then,the self-excited oscillation cavitation nozzle model was established.And design a cavitation tool suitable for increasing CBM production.Through theoretical analysis and Fluent numerical simulation,the jet characteristics of the cavitation nozzle were analyzed.The effects of the ratio and process parameters(inlet flow rate,outlet confining pressure)on the cavitation effect were studied,and finally the laboratory experiments were carried out.By changing the structural parameters and process parameters,the optimal ratio of structural parameters is:d2/dl=1.8?2.2,Dc/d1-5.6?8.4,Lc/Dc=0.2?0.4,?=120°.Based on the optimal structural parameters,the process parameters in the actual construction were optimized,and the optimal range of inlet flow velocity was 45?55m/s.The increase of the surrounding pressure had a suppressive effect on cavitation,however,properly increasing the inlet flow rate can reduce the suppression effect of confining pressure Through experiments,the cavitation performance under different flow rates is analyzed,and the optimal structure obtained by numerical simulation is verified to have strong jet cavitation capability.Comparing different inlet diameters,it is concluded that the optimal inlet diameter is 6mm.The experiment was carried out by changing the diameter of the lower nozzle,and the throttle effect was the best at 12 mm,which was consistent with the simulation results.The research results laid a certain foundation for the application of coalbed methane hydraulic cavitation technology,and also provided a reference for the optimization design of hydraulic cavitation tools.