Research On The Mechanics Of Sidetracking Operations In The Deep Sea Based On Coiled Tubing Technology

Due to advantages in economy and efficient of coiled tubing technology,it has been widely used in most aspects of international offshore oil and gas operations.But there is no uniform process specification for coiled tubing marine operations.And there are very few researches done on the mechanics of coiled tubing marine operations.Thus,supported by National Natural Science Foundation of China and Ph.D Programs Foundation of Ministry of Education of China,this paper studied the technology of coiled tubing marine operations and its mechanics.(1)The process of offshore drilling operation based on coiled tubing is designed,the operation equipment is introduced,the bottom drilling tool combination is analyzed,and the operating environment of outer pipes of coiled tubing is studied.(2)A prediction model of wellbore trajectory prediction is established.And on the basis of this model,the axial force transfer model of coiled tubing working in three-dimensional fixed boundary wellbore is established considered the wellbore trajectory,coiled tubing floating weight,fluid viscous resistance and pressure difference,continuous tubing and wellbore contact force and friction,coiled tubing buckling additional positive pressure and other factors by using FRENET theory,(3)According to the coiled tubing deep-sea drilling operation conditions and shrinkage principle,Pipe-in-pipe test benches of straight pipe and curved pipe section are built up to study axial force transmission and buckling mechanics of coiled tubing under mixed boundary.According to the experimental results,the buckling critical load values in the coiled tube axial force transfer model of the three-dimensional fixed boundary wellbore are corrected,and the axial force transmission model of the coiled tubing in the three-dimensional mixed boundary wellbore is obtained.(4)According to the process of marine sidetracking based on coiled tubing,a full-scale column simulation model is established.The simulation model is calculated by the axial force transfer model of the coiled tubing in a three-dimensional mixed boundary wellbore.Based on the results,the maximum inflow depth of coiled tubing and the control range of the top of the naked eye drilling are analyzed to discuss the feasibility of deep-sea drilling operation based on coiled tubing.