Study On Erosion Wear Law Of Downhole Desander

With the field application of stimulation technology,the sand production of oil wells is intensified,which increases the difficulty of sand control in oil and gas wells.Sand production in oil wells will not only reduce the efficiency of oil and gas exploitation,but also cause erosion wear to downhole tools and ground equipment and shorten the working life of equipment,which has become a common problem in the process of oil and gas exploitation.In order to improve the removal rate of sand particles in crude oil and protect the pump set and downstream tools,the downhole desander has been developed and applied in the field.The tool uses the principle of swirl centrifugal to achieve solid-liquid separation,with simple structure and no moving parts.Erosion wear is the main failure mode of downhole desander,which affects the service life and oil production cycle of the tool.In order to clarify the influence of working condition parameters and structural parameters on the erosion wear of downhole desander and reduce the erosion rate,the following work has been carried out in this paper :(1)A finite element model of erosion wear of downhole desander based on dense discrete phase(DDPM)erosion model was established.The accuracy of the model was verified by laboratory test and previous research data with separation efficiency,tangential velocity and erosion rate as evaluation indexes.The wall erosion wear of downhole desander was simulated by Fluent,and the velocity field,pressure field,particle trajectory and erosion wear characteristics of downhole desander were obtained.(2)According to the actual working conditions of the downhole desander,the main working parameters and their ranges affecting the erosion wear of the downhole desander are determined.The effects of liquid production,viscosity of produced liquid,particle size,particle concentration and particle shape coefficient on the erosion wear of downhole desander were studied by single factor analysis.The variation of maximum erosion rate,separation efficiency and axial erosion rate with each parameter was obtained.Based on the obtained rules,the applicable conditions of downhole desander are analyzed.(3)The effects of spiral pitch,spiral coil number,guide vane number,overflow pipe diameter,taper and underflow diameter on the erosion wear and separation characteristics of downhole desander were studied by using the control variable method.The variation of maximum erosion rate,average erosion rate,separation efficiency and pressure drop with each parameter was obtained.After analysis,the spiral pitch,taper and overflow pipe diameter were selected for response surface optimization.The response surface test scheme was designed by central composite design(BBD).The second-order prediction model of average erosion rate(ER)and separation efficiency(M)was established,and the accuracy of the model was verified by variance analysis.Based on this,the influence of each parameter and the interaction between parameters on the average erosion rate(ER)and separation efficiency(M)was obtained,and the optimal parameter combination was selected to verify the accuracy of the model prediction and the effectiveness of the optimization.(4)The influence of initial external load deformation caused by flow field pressure and suspension load on the erosion wear of downhole desander was studied by fluid-solid coupling calculation method.The erosion-dynamic mesh coupling model of downhole desander was established.The variation of average erosion rate,maximum cumulative deformation,average cumulative deformation and total volume of erosion pit with erosion time was obtained by numerical simulation.The erosion wear of downhole desander is inevitable.In the process of erosion evolution,the erosion rate decreases gradually,but the wall deformation and erosion pit are increasing,resulting in erosion damage.The research results can provide a basis for the structural design and field application of downhole desander.