Solid-liquid Coupling Of The Drill String Transverse Vibration Research

As the increase of oil and gas exploitation and the decrease of oil and gas reserves,in order to improve oil and gas recovery,as well as to reduce the cost of drilling.Horizontal well technology has become a very important drilling technology in modern drilling technology,but because of horizontal well drilling,the drill string is eccentric easily,which results in transverse vibration,and the severe drill string vibration will lead to the fatigue failure of drilling tool and the fracture failure of drill string.Therefore,it is necessary to study the transverse vibration of drill string in horizontal wells.In view of the fatigue failure of drilling tools.taking the vertical well section of a horizontal well in southwest China as the research object.Consider the factor that the drilling fluid density of outside the drill string is bigger than inside,through fluid calculation software,analyze drilling fluid inside the drill string in K-? turbulence model,analyze drilling fluid outside the drill string in discrete phase model,get the curves that pressure of inner wall and outer wall of the drill string about oil well depth,from the curves we can see that any changes in density or viscosity or velocity can cause pressure drop.It is known by the theory of fluid dynamics,The consumption of energy in the pipe can cause pressure drop,the energy consumption is caused by hydraulic loss,the hydraulic loss includes along hydraulic loss and local hydraulic loss,according to the formula of the along hydraulic loss and local hydraulic loss,we can get that when the density or the viscosity or the velocity of flow increases,the pressure drops also increases,and when all the factors are constant,exclude the length of the pipe,the pressure drop is linearly dependent on the length of the pipe,so through compute to establish the pressure function of the drill string inner wall and the external wall about the oil well depth;According to real drilling data,base on kinetic theory,use ANSYS to establish transverse vibration model about the vertical well section of a horizontal wells,consider the effect about drilling fluid with different density inside and outside drill string on transverse vibration,distribute the drilling fluid pressure to the finite element model in the form of load function,through the finite element software to complete the drill string transverse vibration analysis of the vertical well section of horizontal drilling,get the influence of the drilling fluid density,viscosity,velocity and bit pressure on the natural frequency of the drill string transverse vibration.It is that when the values of those factors increase,the natural frequency of the drill string transverse vibration also increase.The research results can provide some practical guidance for the construction of the vertical well section of a horizontal wells.