Research On Mechanical Extending Limits In Rotary Drilling

Rotary drilling plays an important role in the current oil & gas industry,and the reasonable prediction and control of the mechanical extending limits in rotary drilling have attracted much attention.The so called "mechanical extending limit of rotary drilling" means the maximum drilling depth within which a particular rotary drilling system under certain wellbore constraints can guarantee the mechanical security.The mechanical properties of the rotary drilling system are analyzed in depth and the complex mechanical behaviors of local and integral tubular strings and the effects of relevant factors on the mechanical extending limits are studied.A set of theoretical models of the prediction and control of mechanical extending limits is built,which provides a scientific basis of rotary drilling design optimization and operation safety.In the local down-hole tubular mechanical model,a representative section of the local down-hole string under the effects of axial force and torque,boundary conditions,wellbore configuration,etc.is taken as the research object.To solve the local mechanics problem,three methods namely beam-column model,buckling differential equation and energy method are simultaneously adopted.Several main issuses including buckling and post-buckling behaviors of down-hole tubular strings in three-dimensional(3D)wellbore,new boundary condition criterion and the effects of boundary conditions on buckling behaviors,and the comprehensive description of buckling-contact state and the effects of connectors are studied in depth.To overcome the limits due to some assumptions made in the classic down-hole mechanical model,a modified integral model is established by introducing the results from the local mechanical model.Both analytical expressions and numerical calculation procedures of down-hole tubular integral mechanical results while tripping in and out in conventional two-dimensional(2D)and 3D wellbores are given.The prediction models of mechanical extending limits including the tubular slide and rotary tripping in/out limits and casing wear limit are built,which takes the surface and down-hole constraint and operation conditions into consideration.The prediction charts for a variety of wellbore configurations are drawn,and the corresponding constraints and operation conditions are analyzed.Based on our research,the cause of the envelop shape of the current drilling limits is explained from a theoretical point of view.To improve the mechanical extending limit,the principles and procedures of drilling optimization design including wellbore trajectory,down-hole tubular string and drag reduction tools are presented,which are important complements to the regular design methods.