Bionic Surface Texture Design Of PDC For Downhole Drilling Tool Bearings And Its Tribological Performance

Diamond thrust bearings are key components and weak links in downhole power drill tools,and their reliability and lifespan have become a key factor restricting the development of downhole power drill tools.Therefore,prolonging the life of diamond thrust bearings and improving the lubricating friction performance of diamond bearings to achieve the goals of prolonging life,saving energy,and saving materials is an inevitable measure to promote the technological innovation and development of downhole power drilling tools.Diamond thrust bearings are subjected to complex and harsh working conditions such as high temperature,high pressure,friction,vibration,impact,and corrosion during drilling,which can easily lead to failures such as mechanical wear,thermal damage,fragmentation,and shedding of polycrystalline diamond compact(PDC).Nowadays,the drilling industry still faces the problems of low diamond bearing life,frequent trips to replace the thrust bearings of the support section during drilling,which not only increases the cost per foot of drilling,reduces efficiency,but also wastes a lot of time,increases energy consumption and material consumption.The biological microtexture in nature is beneficial for them to better adapt to the natural environment,and it also inspires us to use the "biomimetic tribology" theory to solve the practical problems faced by the drilling industry.It is expected to reduce the mechanical wear of the bearing surface and improve the life of diamond thrust bearing(PDC bearing)by improving the lubrication performance of the bearing surface.The cobalt-removed PDC surface treatment can increase the wear resistance and heat resistance of PDC.Considering the improvement of the wear resistance of PDC itself,we verify the possibility of cobalt-removed PDC as a friction pair material for PDC bearings,to alleviate the failure caused by thermal wear on the surface of PDC bearings.Therefore,based on the above ideas,this paper focuses on how to improve the drag reduction and lubrication characteristics of the PDC bearing surface.(1)Inspired by the non-smooth surface textures of shells and dung beetles in nature,we have combined the surface texturing method of "laser ablation" to select and design bionic models and surface textures suitable for the working conditions of diamond thrust bearings.The orthogonal test method is used to analyze the influence of spacing(angle of radial grooves),width(diameter)and depth on the friction coefficient,and to optimize the texture morphology and the combination of surface texture parameters that are most conducive to the friction and wear of PDC bearings.The lubrication and friction reduction mechanism of bionic textured PDC is revealed by using various microanalytical means.(2)We conducted friction and wear experiments on cobalt-removed PDC under downhole operating conditions to verify the possibility of cobalt-removed PDC as a friction pair material for diamond thrust bearings.Study the tribological behavior and wear mechanism of cobalt-removed PDC under different axial pressure and speed conditions in different drilling fluids.Study the wettability,wear rate,wear height,graphitization degree,and surface microstructure of cobalt-removed PDC to analyze mechanism of wear reduction and wear resistance of PDC in different drilling fluids.(3)By combining cobalt removal with biomimetic texturing,a PDC for diamond thrust bearings with dual functions of wear resistance and drag reduction was developed.The tribological behavior of biomimetic textured PDC under different downhole operating conditions was studied.Under simulated operating conditions of diamond bearings,the lowest average friction coefficient of cobalt-removed PDC with dimples was found to be 0.0334,which is lower than the friction coefficient of untreated PDC(0.0531)by 0.0197,representing a reduction of 37.10%.The introduction of dimples on the PDC surface did not affect the variation of friction coefficient with axial pressure and rotational speed.A comparison of the friction coefficients of untreated PDC without dimples,untreated PDC with dimples,cobalt-removed PDC without dimples,and cobalt-removed PDC with dimples was conducted.Regardless of the varying operating conditions,cobalt-removed PDC with dimples exhibited the best tribological performance.A series of microscopic characterization methods were employed to reveal the drag reduction and lubrication mechanism under the dual effects of cobalt removal and biomimetic texturing.(4)Design and process a diamond bearing with bionic texture and cobalt removal treatment,and verify the effect of bionic texture and cobalt removal on the diamond thrust bearing by comparing it with untreated PDC bearing without dimples,untreated PDC bearing with dimples and cobalt-removed PDC bearing without dimples under friction tests.In this study,by focusing on the two main failures of PDC bearings,mechanical and thermal wear.The bionic surface texture is used to enhance the drag reduction and lubrication characteristics of the PDC surface,and the surface cobalt removal treatment is used to enhance the wear and heat resistance of the PDC surface,revealing the mechanism of bionic texture and cobalt removal treatment on the wear-reducing lubrication of the PDC surface.The combined effect of the two on the PDC surface is used to optimize the tribological behavior of the PDC bearing,providing a strong experimental basis for the bionic texture cobalt removed PDC to be used as a friction pair material for diamond thrust bearings,which will help improve the life and reliability of diamond thrust bearings and promote further research and development of downhole drilling tools.