Study On Coiled Tubing Drilling System Of Downhole Double-motor With Rotating Tubing

Coiled tubing drilling technology has advanced and advantages,and its development trend is in line with the mainstream of today's world drilling technology direction,so coiled tubing drilling technology has been developed rapidly.Although coiled tubing drilling has many advantages,it is still in many deficiencies in practical application.The most obvious deficiency is that the coiled tubing used in coiled tubing drilling cannot be rotatory as conventional drill pipe,which leads to problems such as pressure differential sticking and difficulty in fishing in BHA.In coiled tubing drilling horizontal,due to borehole annulus area is small,low drilling fluid velocity of slimhole cleaning difficulties,make the process of coiled tubing drilling string and BHA prone to grit,adhesion sticking and so on,at the same time,coiled tubing drilling string friction increasing,lead to string buckling occur,when the pipe string buckling reaches a certain degree after there will be coiled tubing drilling "locking" phenomenon,bring great difficulties to the normal drilling.In order to solve the problem of coiled tubing drilling string can't rotate this paper established a coiled tubing drilling based on double-motor drive down-hole string rotating drilling system,aiming at improving the efficiency of horizontal well annular space cuttings transport,increase the coiled tubing drilling axial force transmission capacity,reduce the string along the horizontal section of friction resistance,increase drilling horizontal Wells in coiled tubing extension ability.The main research contents are as follows:(1)Establishment of the drilling system model of downhole double-motor rotary string.Based on conventional coiled tubing drilling system,the model of drilling system with double-motor rotating string is established in this paper.This paper introduces the working principle of downhole rotary drill string system in secondary pipe drilling.The components of the rotary drill string system in coiled tubing drilling are analyzed,and the assembly of the rotary drill string is determined.(2)Force analysis of rotary string of drilling system with twin motors.In this paper,the axial load and torque of the string during the rotating drilling of coiled tubing are theoretically analyzed,and the stress state of the rotating section in different positions of the borehole is analyzed by using the 3D flexible rod model of coiled tubing,and the torque required by the upper motor and the axial force distribution of the string in different states are determined.Finally,by using the solid-liquid coupling method of ANSYS,considering the influence of the change of flow field on the force of the horizontal rotating string in the rotating state of the string,the counter torque on the upper end of the rotating string at different rotating speeds under concentric and eccentric states is obtained.(3)Analysis of annular flow field in rotating string section of drilling system with twin-motor rotating string.Using CFD software to coiled tubing Wells section and part of the rotating string on the wellbore annulus object to study the influence of fluid flow,established a coiled tubing annular space three-dimensional fluid domain model,the Euler multiphase flow model and Realizable k-? turbulence model and SIMPLIC algorithm for numerical.(4)Analysis of annulus cuttings transport efficiency and its influencing factors under the condition of rotating pipe string.Under the condition of rotating pipe string,CFD software was used to analyze the influence of different influencing factors on the utilization efficiency of cuttings in the annular flow field of rotating pipe string,and the movement and settlement rules of cuttings in the annular flow field of rotating pipe string in the wellbore were obtained.Through this study,it can be known that the rotation of the string in the twin-motor drilling system can reduce the friction resistance on the string,reduce the annular pressure drop,and at the same time,the rotation of the string can also improve the well cleaning capacity.In order to improve the horizontal extension ability of coiled tubing drilling and reasonably design the drilling system of partially rotating string in horizontal well section of coiled tubing,the theoretical basis is established in this study.