Research On Annular Pressure Of Slim Hole In Ultra Deep Well Considering Drill String Rotation And Buckling

The prediction of annular pressure drop during the drilling of deep wells and ultra-deep wells is inaccurate.This may lead to imbalance in bottom hole pressure and cause safety incidents such as leaks and blowouts,so the accurate prediction of annular pressure drop is of utmost importance,for well control,The optimization of drilling parameters and controlled pressure drilling During the drilling of horizontal wells and directional wells,the drill string is susceptible to buckling due to the axial load,and the buckling of the drill string will not only greatly affect the annulus hydraulics,but also have a certain impact on the annular pressure drop.In order to achieve an accurate and convenient prediction of the pressure drop of the buckling annulus under the condition of drill string rotation,Based on the theory of fluid mechanics,this paper establishes the fitting model of the annular pressure drop of a yield power-law fluid under the conditions of the drill string rotation,the concentric(eccentric)annular pressure drop mathematical model affected by the drill pipe joint and the Simplified model of annular pressure drop considering drill string rotation and buckling;Secondly,based on the Fluent software,a simulation model considering the rotation of the drill string,joints,and buckling conditions was developed,and related simulation studies were carried out.The main research results obtained are:(1)A concentric annular pressure drop fitting model that considers the effect of drill string rotation has been established and using this model to carry out analysis of relevant influencing factors.annulus pressure shown linear or quasi-linear change with changing of fluid yield stress and consistency index,and shown index change with changing of fluid behavior index,rotation speed of the Inner tube,diameter rate and dimensionless eccentricity.Applying Fluent Software to Simulate Annular Pressure Drop Considering Drill String Rotation,The simulation results are compared with the experimental results to verily the accuracy of the simulation results.The model results are compared with the simulation results and the experimental results,indicating that the fitting model has high accuracy;(2)A concentric(eccentric)pressure drop mathematical model considering the influence of drill pipe joints was established and using this model to carry out analysis of the influencing factors,At the same time,Fluent's software was used to conduct a simulation study of the annular pressure drop considering the effects of drill pipe joints,Comparing the results of the simulation model with the results of the mathematical model,the error range is±5%in the concentric annulus and ± 10%in the eccentric annulus,and the error is ±15%when the drill string rotation and the joint are considered simultaneously;(3)A simplified model of the annular pressure drop considering the buckling effect of the drill string was established and using this model to carry out analysis of the influencing factors,As the axial distance increases,the annular pressure drop ratio shows a periodic change.Within a sinusoidal flexion interval,the ratio increases first and then decreases,with the increase of yield value,consistency coefficient,and annular flow rate,the ratio of annular pressure drop remains basically unchanged,with the increase of the fluidity index,the ratio of the inner and outer diameters of the annulus and the eccentricity,the trend is gradually decreasing.At the same time,Fluent software was used to establish a simulation model of the annular pressure drop when considering the buckling of the drill string.The model results were compared with the simulation results,and the error range was ±5%when the drill string rotation was not considered.(4)A simplified model of the annular pressure drop considering the effects of drill string rotation and buckling is established.The pressure drop of the annulus decreases with the increase of the speed of the inner tube.Under the condition that the speed of the inner tube remains the same,the pressure drop of the annulus increases with the increase of the yield value,consistency coefficient,and fluidity index and decreases with the maximum eccentricity increases,Comparing the model calculation results with the simulation results,the error range is ± 10%.