| With the increasing depth of oil and gas wells and scientific exploration wells in China,the complex bottom hole environment puts forward higher requirements for the performance of drill pipes..Because of its high specific strength,low density and good acid and corrosion resistance,aluminum drill pipe is considered as the preferred option for deep and ultra-deep well projects,and has been successfully applied in many deep and ultra-deep wells.However,aluminum drill pipes also have disadvantages such as poor thermal stability,lack of wear resistance and unreliable connection with steel joints,which pose a challenge to the safety of deep and ultra-deep wells.In order to minimize these disadvantages in actual engineering,it is necessary to have a clear understanding of the motion of aluminum drill pipe and the ultimate strength of the weak part for aluminum drill pipe under deep and ultra-deep well conditions,so that reasonable drilling parameters can be selected to avoid the load of aluminum drill pipe exceeding the ultimate value and unnecessary wear.Therefore,this paper investigates the whirl characteristics and ultimate strength for aluminum drill pipe considering temperature factor.(1)The whirl model of the drillstring based on the shell element is established and compared with the existing experimental data to verify the accuracy of the model from three aspects: displacement curve,motion trajectory and motion state.The motion of the drillstring is visualized.The effects of rotational speed,weight on bit,friction coefficient and drillstring-to-wall clearance on the whirl state of the drillstring are studied.The effects of different motion states on velocity,acceleration,contact force and friction force are analyzed.Finally,the model is re-validated from the principle of minimum dissipated power consumption rate,completing the mutual validation between simulation-experiment-theory and verifying the accuracy of the shell element model from several aspects.The study shows that the rotational speed has a positive effect on the formation of backward whirl.From low rotation speed to high rotation speed,the drillstring go through the transition process of forward whirl-random-backward whirl.When the motion is in forward whirl,the velocity and acceleration increase proportionally with the increase of rotational speed,and there will be a corresponding increase of contact force and friction force.When it is in the backward whirl state,the revolution frequency of the drilstring is no longer equal to the rotation frequency,and its magnitude is affected by the radius of the drillstring and the radius of the wellbore.Besides,there is an increase in speed,acceleration,contact force and friction that exceeds the increase in rotation speed.Weight on bit has little effect on the motion of the drillstring,velocity,acceleration,contact force and friction force.The increase of friction coefficient also makes the drill string more susceptible to backward whirl.There is a substantial increase in velocity,acceleration,contact force and friction after backward whirl formation.However,the effect of continuing to increase the friction coefficient on the contact force and acceleration will be very weak after the backward whirl is formed.The increase of drillstring-to-wall clearance causes the drillstring to undergo the transformation of the motion process: forward whirl-random– backward whirl-no contact forward whirl.The increase in velocity,acceleration,friction and contact force will be smaller for the backward whirl caused by the increase in clearance.(2)The whirl model of the full-well size aluminum drill pipe is established using the beam-shell combination element,and the effect of temperature gradient is taken into account.Taking the drillstring structure of SK-2 well as an example,the whirl characteristics of SK-2 well are analyzed to verify the rationality of drilling parameters and drilling method of SK-2 well.The effects of aluminum drill pipe position,temperature and rotational speed on the whirl motion of the drillstring are also studied.The analysis results show that: compared with the position of aluminum drill pipe away from the drill bit,when it is close to the drill bit,it will aggravate the transverse vibration and whirl of the drill string to a certain extent.When the aluminum drill pipe is at the bottom,the temperature has a limited influence on the whirl,and the influence on whirl mainly depends on the degree of decrease in the elasticity modulus of the aluminum alloy.The rotation speed has a strong influence on the whirl motion,and different parts of the drillstring shows different motion states.(3)A parametric 3D hexahedral mesh modeling program for aluminum drill pipe and steel joint assembly is written based on matlab software.The elastic-plastic finite element model of aluminum drill pipe and steel joint assembly is established by combining Johnson-Cook constitutive model and fracture criterion.The accuracy of the model is verified by small-size experiments.Subsequently,the ultimate tensile and ultimate torsional analyses are performed for 147×13 mm 7075 aluminum drill pipe and steel joint assembly.The ultimate strength of the tensile-torsional complex force,ultimate anti-loosening performance and failure mode under different interference are analyzed.The analysis results show that the established model has good agreement with the experiment.The effect of interference on the tensile strength is small,and the torsional strength increases with the increase of interference,but the enhancement effect is weakened with the increase of interference.For tensile-torsion complex force,small tensile strength has almost no effect on torsional strength when interference is small,but large tensile load makes the torsional strength decrease rapidly.At large interference,the weakening effect of tension on torsional strength is always present,and this weakening effect is strengthened as the tension increases.The limit antitorsional property will be strengthened with the increase of interference,but this strengthening effect disappears after the interference exceeds the limit value.(4)The effect of high temperature on the ultimate strength of 2024 aluminum drill pipe and steel joint assembly is studied.Material experiment,cold assembly experiment and small size tensile experiment at high temperature are conducted and verified with numerical simulations to ensure the accuracy of the experiment and numerical models.The interference theory is further supplemented by considering the effect of temperature.Based on the accuracy of the numerical model,the stress,strain,tensile and torsional analysis of aluminum drill pipe and steel joint assembly for 147× 13 mm scale at high temperature is carried out.The effect of high temperature on the ultimate strength under combined tensile and torsional loads is also analyzed.The results of the analysis show that high temperature reduces the maximum amount of interference that the aluminum drill pipe and steel joint assembly can withstand.At the same time,the rise in temperature further increase the interference,which also increase the high stress region and high strain region.High temperature decreases the tensile strength and torsional strength,and the higher the temperature,the more obvious the effect.High temperature also decreases the strength under tensile-torsional complex load.The higher the temperature is,the faster the ultimate strength decreases.According to the calculation results,the safe use parameters of aluminum drill pipe under different temperatures are plotted. |
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