Study Of Drill String Dynamic Characteristics In Highly-Deviated Borehole Through Simulation Experiment

Accompanying with the development of drilling technology and the deepening of oil and gas exploration,numerous advanced technology such as highly-deviated wells,directional wells and multitude wells have been more mature and widely used.In addition,some new technology including rotary steerable drilling and geo-steering drilling have received high attention and is developing rapidly.However,the relevant theoretical and experimental researches of drill string dynamics are relatively less than practice,and how to predict and control borehole trajectory scientifically and effectively has always been the emphases and difficulties in drilling engineering field.The drill string dynamics research is the cornerstone of the whole drilling engineering so it is quite essential to study the drill string dynamics characteristics in highly-deviated well hole.This paper is based on the indoor simulation device of drill string dynamics in China University of Petroleum(East China)and the main purpose is to explore the dynamic characteristics of drill string in highly-deviated well including lateral vibration feature,WOB fluctuation feature and bit force.The similarity criterion of simulation experiment has been deduced by the method of dimensional analysis and a simulation experimental device for investigating the motion states of bottom drill string in highly-deviated well has been designed and built up according to the geometric similarity ratio 1:10.This device is able to adjust rotary speed and WOB instantaneously to simulate different combinations of drilling parameters.The horizontal device consists of 16 sensors including pressure sensors,eddy current displace sensors and lateral force sensors.They are used to measure all the dynamic parameters when the drill string is rotating.Furthermore,an experimental scheme have been compiled on the basis of field reality and specific programs have been written to process the original experiment data.The motion trajectory of drill string in borehole have been restored accurately by the intelligent compensation algorithm.The change law of drill string's lateral vibration frequency and vibration amplitude have been studied as drill parameters vary;the WOB fluctuation frequency and fluctuation amplitude have been analyzed under different conditions,and the calculation method of WOB fluctuation amplitude have been put forward;the computed method of directional force and well-deviation force have been deduced based on the mechanical model of bit lateral force,and the change law of the two forces have been analyzed.Designed the concept of “average bit force” to research the change tendency of highly-deviated well trajectory.