Optimization Design Of The Static Push-the-Bit Rotary Steering Bottom Hole Assembly

Rotary steering drilling system(RSS)has brought a new revolution to the development of drilling engineering.It can not only adjust the borehole deviation and azimuth automaticly and flexibly rapidly but also improve the drilling speed and drilling safety.In order to improve the development and application level of static push-the-bit RSS,the steerable force and tool orientation of RSS tool must be accurately forecasted.Therefore,establishing accurate mechanics analysis model of static push-the-bit RSBHA is significant for the development of rotary steering tool.On the basis of full understanding BHA mechanics characteristics and structure analysis method of rotary steering tool,analytical model and solving method of RSBHA in 2D and 3D wellbore are established by using the beam-column method.Thus,the expression of bit side force and bit tilt angle can be concluded.Further,the drilling tendency angle is obtained,which can provide guide for the prediction of wellbore trajectory.The improvement of build-up rate of the RSBHA is through the analysis of the drilling tool structure.In the paper,four aspect are discussed including the drilling parameters(weight-on-bit,the magnitude of the steerable force),tool structure parameters(steerable force position,the location and diameter of first stablizer and the parameters of the flexible sub).This can provide a reference for the development of the rotary steering tool.In order to avoid the steering rib contactting with wellbore,the diameter and position of the first stabilizer also should be discussed.In this paper,the design series of thick steering rib and first stabilizer are recommended.Furtherly,the effects of wellbore elasticity on RSBHA tool are discussed.The model of drill string and borehole contact is established by using the theory of Hertz contact.The borehole curvature and rock elastic modulus are analyzed for enhancing the drilling bit side force.