Simulation And Experimental Study On Erosion Wear Of Copper Alloy Barrel Of Measurement While Drilling (MWD)

Measurement while drilling(MWD)has been widely used in petroleum drilling engineering because it can realize borehole trajectory monitoring and improve the drilling speed.However,when the solid particles entrained in the fluid impact the wall of the equipment,it would cause the damage of the wall,bringing about the degradation of equipment performance and also the shortening the service life of MWD instruments.To prevent the sudden breakdowns and expensive repairs,it is necessary to recognize the location of equipment wear and accurately predict the erosion rate of equipment.However,the test monitoring method costs much in both time and money,existing a lot of uncertain risk.Computational fluid dynamics(CFD)is a fairly effective method to predict erosion rate.CFD could make up for the experimental defects and observe the particle characteristics(impact velocity,impact angle and number of impacts)that are difficult to achieve in the experiment,which is wildly applied into equipment erosion prediction.This article adopts the method of combining field test and numerical simulation to study the erosion process and erosion mechanism of the MWD outer cylinder.The test was carried out in the field environment provided by a petroleum engineering company.Based on CFD,erosion prediction mainly includes three steps:(1)Gain the mobile solution;(2)Particle tracking and calculation of particle characteristics;(3)Erosion model calculation.Besides,in terms of high pressure conditions,there is a need to consider the effect of stress.In addition,a user-defined function(UDF)code was developed to calculate the particle characteristics and erosion rate,and compare the calculated results with the test ones to ensure the reliability of the stimulated results.According to the grid research,appropriate meshing,near-wall processing and turbulence model selection are the optical keys to obtain a accurate CFD erosion prediction.The calculated results show that the Realizable?-?turbulence model can predict the erosion profile in the upstream area more accurately,and the erosion depth is in good agreement with the experimental data.But there exists over-predict of the total mass loss in the downstream area.Compared to that,the RSM turbulence model have a better prediction of the total mass loss.The traditional erosion model is hard to accurately predict erosion rate under high pressure condition without considering the effect of stress.In order to study the effects of different parameters on the erosion wear of MWD outer cylinder,the effects of fluid displacement,particle concentration and particle diameter on the erosion wear of MWD outer cylinder were calculated based on CFD.The results show that the erosion wear of MWD is mainly distributed in the upper region,and the particle concentration and displacement can increase the erosion rate.The effect of particle diameter on erosion rate first increases and then decreases,but the total mass loss decreases.In terms of the test measurement method,it involves both of macro measurement and microopic observation.In the aspect of macro,the total mass loss of the MWD outer cylinder before and after the erosion is measured with an electronic balance,and the local depth is measured with the super-focus three-dimensional profile technology.The results show that the erosion wear is mainly distributed in the area of sudden shrinkage,and the overall trend of erosion rate decreases from top to bottom.In addition,high pressure condition would aggravate the surface wear of the MWD outer cylinder and expand its erosion range.In the aspect of micro,the samples were studied with a Super Depth 3D microscope to understand the micro-structure of the MWD outer cylinder.It has been demonstrated that computational fluid dynamics(CFD)and exper-imental approach can be used to identify and explain the erosion mechanisms in different regions where the surface morphologies reveal four erosion patterns,namely,micro-cutting,cracks,pits and plastic deformation.NiCrAlY/Al₂O₃-20wt%TiO₂ was used for gradient coating of MWD outer cylinder.The test results show that NiCrAlY/Al₂O₃-20wt%TiO₂ has good erosion resistance and compression resistance,which greatly improves the service life of MWD instrument under severe working conditions.