The Spray Gun Morphology After Erosion By Water Jet Multi-Cluster Fracture

The hydraulic jet multi-cluster fracturing technology is a novel volumetric stimulation method which integrating multi-cluster perforation,staged fracturing and isolation.It has the advantages of fracturing efficiently and generating fractures accurately.However,the high-speed sand-containing fracturing fluid flows through the spray gun which cause the erosion of the spray gun inevitably.Therefore,controlling the erosion characteristics at the inner wall of the spray gun is an important prerequisite for improving the successful of fracturing.For solving the scientific question that the mechanical mechanism of the erosion process,we did various numerical simulations and on-sites experiments.The on-sties experiments which applying the actual material were be conducted to show the effect of impact rate and angle on erosion rate.The impact erosion angle function which suits the real situation on-sties was introduced and this function corrected the Finnie erosion calculation model for hydraulic jet fracturing conditions.Based on the Discrete Phase Model（DPM）and Realizable k-epsilon model,and combined the function of erosion angle,we established the hydraulic jet multi-cluster fracturing spray gun model and operated various simulations.The results show the characteristics of the internal flow field of the spray gun and the erosion differences between the upper and lower cluster of the spray gun.The influence rules of some key parameters,such as fracturing displacement and the size of sand particles,on erosion rate were also be analyzed from the results.The position of the erosion in the upper and lower cluster spray gun and the erosion volume can be obtained by scanning the internal flow field from the used spray gun in three-dimensions.The results can match the numerical results.From the scanning results,we can find that serious erosions happened around the upper area of the lower cluster’s entrance and the lower area of the upper cluster’s entrance.The volume of the erosion on the lower cluster is larger than the upper cluster.The eroded volume in the lower cluster’s entrance area is 1.3 to 1.9times larger than the upper’s.The erosion rate has a negative correlation with sand size,and it has a positive correlation with flow rate and impact velocity.The erosion rate also has a parabolic relationship with the erosion angle.The erosion velocity in our experiment range between 4.44×10^-5～1.74×10^-4 kg/（m²·s）.From the microanalysis of the erosion section,we can find that when the impact angle is small,cutting failure will mainly cause the micro-erosion;When the impact angle is large,the impact crushing damage is dominant.We also introduce some suggestions on improving the spray gun.We suggest that enhancing the inner wall at entrance area of upper cluster and inner wall of upper cluster.Increasing the coating in those area can be a useful improvement.The results enrich the multi-cluster erosion theory and may provide the necessary theoretical basis for improving the structure of multi-cluster spray gun and improve the success rates of multi-cluster fracturing.