首页|Optimal design of drag reduction oscillators by considering drillstring fatigue and hydraulic loss in sliding drilling
Optimal design of drag reduction oscillators by considering drillstring fatigue and hydraulic loss in sliding drilling
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NSTL
Practice has proved that drag reduction oscillators can be used to decrease the axial friction and increase wellbore extension effectively in sliding drilling.However,the complicated mechanical behaviors of drillstring with drag reduction oscillators have not been revealed sufficiently,and there has no theoretical method to optimize drag reduction parameters.In this paper,an optimization design model of drag reduction oscillators is built with drag reduction efficiency as the target,and the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity.Further introducing the initial conditions,boundary conditions,and continuity conditions,the finite differential equation of drillstring vibration is obtained and solved.Next,combined with the oscillation propagation length and the installation position optimization models,the orthogonal experimental design method is applied to optimize the relevant parameters.In the optimization process,the constraint factors,including drillstring failure and hydraulic loss,are considered.Finally,the new model is applied to a field case study,in which the drag reduction effects of drillstring with and without oscillators are compared,and the impact of relevant factors on drag reduction are analyzed.The results show that the equivalent friction coefficient near the oscillator installation position is significantly reduced,whereas the hook load and weight on bit(WOB)are increased significantly with drag reduction oscillators.With the increase of amplitude or frequency,the propagation distance of the oscillator increases.The amplitude of vibration force and the number of oscillators are the two main factors affecting drag reduction efficiency.Three hydraulic oscillators with vibration amplitudes of 40 KN are recommended,and the drag reduction efficiency is 51.78%.However,excessively large oscillation amplitude may lead to drillstring failure and too many oscillators will increase the hydraulic loss a lot.Therefore,there are optimal values of oscillation amplitude and the number of oscillators.The research results are of significant guiding significance for optimal design and safety control of drag reduction oscillators in sliding drilling.
Sliding drillingFriction forceDrag reduction oscillatorDrillstring failureHydraulic loss
Wenjun Huang、Deli Gao、Xiaolei Shi
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MOE Key Laboratory of Petroleum Engineering,China University of Petroleum,Beijing,102249,China
NSTL
