Influence of a combined bearing on the buildup rate of a wellbore trajectory control tool

Abstract

Conventional methods cannot accurately predict buildup rate. In this study, an algorithm was developed to predict the geometric deflection rate of the tool considering the influence of the radial displacement of a combined bearing. Three-point geometry was used to calculate the buildup rate and its relationship with the radial displacement of the combined bearing. The relation between the maximum spindle deflection and the load of the combined bearing was also determined by treating the spindle as a statically indeterminate beam. To consider the internal structural parameters of the combined bearing, a mathematical relationship was obtained between its load and radial displacement with the Stribeck maximum rolling element load formula and Palmgren roller bearing displacement formula. The influence of the structural parameters of the combined bearing on the buildup rate was analyzed, and the results showed that the buildup rate can be increased by increasing the thickness and pre-compression of the disc spring and decreasing its diameter ratio and the radial clearance of the self-aligning roller bearing. An experimental device was used to obtain test results with different maximum spindle deflection values. In particular, the error was less than 1% when the maximum spindle deflection was more than 4 mm.

Keywords

• downhole directional drilling equipment
• point-the-bit rotary steerable tool
• combined bearing
• buildup rate
• mathematical model