Deepwater Drilling String Dynamics Analysis And Research

For harsh environment and complex condition in deep water drilling,deep water drilling string happens to failures easily.How to analysis characteristics of deep water drilling pipe to avoid drilling string failure is essential.This paper introduces the research methods of deep water drilling string dynamics(linear micro-element method,the gap element method,finite element method,beam bending method,etc.)and under different drilling environments,the best method will be used to improve the accuracy of calculation.Currently our country deep water drilling technology is still in its infancy.We must study deep water drilling drill horizontal,vertical,and torsional and mutual coupling dynamic about how to incur in-depth.The main work contents are as follows:Deep water drilling horizontal section column longitudinal dynamics models are preferred to choose.By numerical simulation,the damper stiffness and suspension stiffness internet relationship with the natural frequency;Horizontal section drilling string nonlinear finite element model is established to get WOB and other dynamic external load influence on the natural frequency.Drilling string horizontal section lateral vibration finite element equation is established.With considering drilling fluid additional force on drilling string,the natural frequency firstly decreases and then increases.When the rotation speed reaches a certain value,the vibration acceleration suddenly increases.For single drilling string with revolution and rotation,the smaller annular clearance and the borehole diameter are and the higher the rotation is,the more severely lateral drilling string vibrates and the greater the alternating stress is.When the drilling string reverses,the longer the distance from the point,the more severely lateral drilling string vibrates.When torsional resonance occurs,the higher the rotation is,the more obvious drill stringing dynamic effect is.The borehole diameter,whirling angular velocity and the size of the drilling string directly result in whirling vibration.Under normal circumstances,the larger the angular velocity is,the more easily drill string whirling occurs.Stick-slip vibration cycle is generally longer than the sliding.Stick-slip vibration cycle becomes longer with the length of the drilling string.The stick-slip vibration period of the drilling collar is generally longer than the drilling pipe.Deep water drilling string unit nonlinear couple dynamic finite element equation is established.Through matrix change,with the increasing of n,the natural frequency of drill string increases.Through numerical simulation results,with the smaller the fluid density inside and outside drilling string and the eccentricity is and the higher the rotation is,the larger the natural frequency of the drilling string is.Nonlinear dynamic calculation and result are close to the well site operations with comparing.Experimental analysis WOB cyclical fluctuations,studied the relationship between the drill string vibration intensity of the drill press,speed through.Solving Wave drill reduction finite element dynamic equations,numerical simulation of different speed,WOB,drilling length of the drill string coupled vibration frequency.The higher the speed of discovery,the higher WOB,the shorter the length of the drill string are,the easily the drill string occurs resonance.Field data studies the relationship between speed and WOB with drilling string vibration.The use of dynamic security assessment method called Dynamic Security Assessment for a deep water well summarizes that the best rotation is 60~110rpm and WOB is 80~120KN.To ensure the safe operation of the well,the parameters do not exceed the rotation speed 110 rpm,WOB not exceed 120 KN.It provides drilling safety reliability advice for deep water drilling string.