Study On Interaction Between Riser And Drill String And Wear Of Bottom Joint

In the operation of offshore drilling platforms,the riser and the drill string are one of the essential components for achieving the drilling function.Due to the environment,the elongated riser is prone to bending deformation under the action of ocean loads such as wind and waves.The bending deformation of the riser will have a huge impact on the drilling platform.(1)The deformation of the riser will cause the internal working pipe string such as the drill string to contact the riser pipe,which will aggravate the wear between the pipe string,reduce the service life of the inner working pipe string and the riser pipe,and cause the leakage of the drilling fluid;(2)The wear of the internal working pipe string and the riser will increase the energy loss,increase the power consumption of the drilling system,and reduce the efficiency of offshore drilling;(3)In the vicinity of the subsea wellhead,the connection between the riser and the Blowout Preventor(BOP)is connected by a ball joint.The deflection of the riser will inevitably lead to sharp corners near the ball joint,so the internal drill pipe works near the ball joint.At this time,intermittent sharp corner contact is formed,which is very large,and the destructiveness to the drill pipe and the ball joint is also very large.This paper mainly studies the above three problems.(1)Study the effects of environmental loads such as waves,wind waves and ocean currents on the riser,and then obtain the deflection of the riser and the equation of the deflection curve;(2)Based on the shape position equation of the riser and the steady-state tension-torque equation combined with the column mechanics,the contact and force of the inner working column and the riser are studied,and the contact force distribution between the columns is obtained.(3)For the intermittent sharp angle contact near the ball joint,the mechanical model is established by using the theory of vertical and horizontal continuous bending beam,and the contact force near the sharp corner is solved.At the same time,the vicinity of the subsea wellhead is explored,and the blowout preventer and the riser are straight.The influence of the plug-in joint on the contact wear,and finally the contact force near the joint caused by the two joint methods is compared to obtain a better joint structure.In this paper,the mechanical model of the deflection of the riser under the action of wind and waves is established,and the mechanical model is solved by Visual Basic programming software.At the same time,based on the steady-state tension-torque equation,the mechanical model of the interaction between the riser and the internal working string is established,and the distribution of contact force between the columns is programmed.Finally,based on the theory of longitudinal and transverse bending beams,the ball joint is established.The mechanical model of the intermittent contact near the head is simultaneously programmed to obtain the contact force of the sharp-point contact,and compared with the in-line connection method,it is found that the ball joint will aggravate the contact wear between the columns.