Abstract

Abstract. The drilling pipe used in slim-borehole drilling performs well due to its low cost and high efficiency. Good sealing properties and coupling strength are the two keys to ensure that the pipe works correctly. In this paper, a 68 mm diameter drilling pipe and its joint are developed. On the basis of Lame's theory, the contact model of the joint thread is represented under different axial force, makeup torque, and pressure difference between inner and outer pipe. This model provides a good reference for judging the quality of sealing of the joint thread. The analysis software ANSYS\\Workbench is applied to stimulate the distribution of contact stress and sealing properties. A premium condition for drilling has been proposed, which provides a good theoretical basis for slim-borehole drilling.

Highlights

  • The drilling pipe used in slim-borehole drilling performs well due to its lower cost and higher efficiency (Zhang et al, 2015)

  • Many studies have been conducted on the joint thread according to American Petroleum Institute (API) standards (American Petroleum Institute, 1995)

  • Wang et al.: Model of a new joint thread for a drilling tool and its stress analysis used in a slim borehole

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Summary

Introduction

The drilling pipe used in slim-borehole drilling performs well due to its lower cost and higher efficiency (Zhang et al, 2015). Due to it being the most fragile component of the whole driving pipe string (Zhou, 2009), the joint thread has attracted many researchers’ interest to improve its sealing quality (Li et al, 2014) and connection stress, which are the key characteristics and areas of research emphasis with regard to the drilling pipe (Gong, 1995). Y. Wang et al.: Model of a new joint thread for a drilling tool and its stress analysis used in a slim borehole. A premium condition for drilling has been proposed, which provides a good theoretical basis for slim-borehole drilling

Structure of the drilling pipe
Theoretical foundation and assumptions
Makeup torque influenced by the axial force
Contact mechanical model of the joint
The circumferential stress model of joint
Model and criterion of the sealing joint
Finite-element modelling
Element selection and meshing
Boundary conditions and loading
Pipe joints and its connection states
Stress distribution of pipe joints
Joint state under allowable tensile force
Joint state under allowable yield force
Stress change principle with three different connection types
Calculation of the premium makeup torque
Conclusions
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