Simulation experiment on the cooling of PDC drill bit cutting teeth in bottom-hole fluid-structure coupling environments
[Objective]Polycrystalline diamond compact(PDC)drill bits have become the primary choice for developing deep resources.However,thermal damage during drilling considerably influences the drilling efficiency and drill bit lifespan.Owing to the complex bottom-hole environment,conducting indoor experimental research on the cooling of PDC drill-bit cutting teeth is challenging.[Methods]Therefore,this study utilized computational fluid dynamics to simulate cutting tooth cooling in a bottom-hole fluid-structure coupling environment,considering various influencing factors.This study targeted the thermal damage issue of a PDC drill-bit cutting teeth.A PDC bit simulation model was established using an 8-1/2"six-blade PDC bit as the basis.The wellbore rock,PDC bit,and wellbore flow field models were integrated to create a PDC bit bottom-hole cooling fluid-structure coupling model.Owing to the complexity and irregular shape of the PDC drill-bit and bottom-hole flow field model,an unstructured tetrahedral mesh with high applicability was selected across the computational domain.An expansion mesh was placed at the interface between the PDC drill bit and the fluid,and the mesh around the cutting teeth of the PDC drill bit was refined.Based on the actual drilling conditions,four simulation schemes were designed using experimental methods to control the variables.Simulation experiments were conducted on parameters such as the drilling fluid displacement,drilling fluid temperature,cutting tooth heating power,and formation heating power.[Results]The simulation experiment results were analyzed to observe the temperature changes in the cutting teeth at different positions of the drill bit under the influence of various factors in the bottom-hole fluid-structure coupling environment.To explore the sensitivity of cutting teeth cooling under the bottom-hole fluid-structure coupling environment to four influencing factors—drilling fluid displacement,drilling fluid temperature,drilling machinery parameters,and formation temperature—a four-factor,five-level orthogonal experimental design scheme was adopted.Simulation experiments were conducted,experimental data were extracted,and range and variance analyses were performed on orthogonal experimental results.The sensitivity factors affecting cutting tooth cooling were as follows:drilling fluid displacement had the greatest impact on the cooling of the drill-bit cutting teeth,followed by drilling mechanical parameters and drilling fluid temperature.The influence of the formation temperature on cooling was relatively insignificant.[Conclusions]A comparison of the cooling effects of cutting teeth at different positions on each blade revealed uneven cooling,and cutting teeth directly flushed by the drilling fluid at the nozzle had better cooling effects.In the design of the drill-bit structure,the number of cutting teeth directly flushed by the nozzle jet should be maximized.The research results provide a theoretical basis for exploring the thermal damage problem of cutting teeth during the rock-breaking process of drill bits under bottom-hole fluid-structure coupling conditions and for optimizing the design of PDC drill bits.
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