Study On Cutting Casing Of Coalbed Methane Abandoned Well By Abrasive Water Jet

When the coalbed methane well reaches its production life, the casing left in the well has a great impact on the subsequent mining operation. It may damage the mining machine, which causes great economic loss. What’s more, the spark caused by the collision between coal mining machine and the casing may trigger gas explosion, which will bring great security threat. There are some hidden safety problems using mechanical cutting methods. During the cutting process local high temperature and spars are produced. So it is unsuitable for coal mine where exists coalbed methane. Abrasive water jet cutting is a kind of cold and efficient cutting technology. It will not generate local high temperature and spark, which is well adapted to coal mine.This paper analysis the effect of channel shape of different nozzles on jet flow field by numerical simulation, including constant variable velocity gradient nozzle、streamline nozzle、conical nozzle、circular-arc nozzle、cylindrical nozzle、double circular-arc nozzle. The results show that the streamline nozzle is the most suitable nozzle for abrasive water jet cutting, which generates small diffusion angle, long potential core, high axial velocity and slow velocity attenuation. Cylindrical nozzle has the worst effect. The numerical simulation of parameter optimization of streamline nozzle shows that the best dimensionless systolic length is about seven and the optimal length-diameter ratio is about four.The effect of various parameters on the cutting efficiency is studied by experiment, including pump pressure, repeated cutting times, jet distance, the inner flow channel shape of nozzles, volume concentration of abrasive and abrasive categories. The results show that The cutting effect of streamline nozzle is better than the conical nozzle. Higher jet pressure, more repeated cutting times, higher volume concentration of abrasive lead to larger cutting depth. The experiment shows that there exists an optimum jet distance, which is 4.5 times of nozzle exit diameter in this paper’s experimental condition. The cutting depth of four kinds of abrasive from low to high are quartz sand、silicon corundum、iron sand、garnet. Results from numerical simulation are in good agreement with the experimental results.Abrasive jet cutting device for coalbed methane well is designed based on the characters of AWJ cold cutting. This device consists of two parts, a traversing mechanism and a lifting mechanism. The hydraulic cylinder is selected as the actuator of traversing mechanism. The motion direction of nozzle is regulated by the stretch-out and draw-back of piston rod, so as to realize the liner motion of the nozzle. Using screw drive, the lifting mechanism can meet the demands of cutting at the different height.