Risk analysis of the static push-the-bit steerable ribs falling into wellbore wall

Abstract

Rotary steerable system (RSS) is the most advanced and representative directional drilling system. The static push-the-bit RSS relies on three steerable ribs to support on the wellbore wall to provide steering force. The wellbore wall may yield and plastically deform due to the pushing force from the steerable ribs. The finite element method is used to simulate the process of the steerable rib falling into the wellbore wall while drilling ahead. The factors that may affect the wellbore deformation and failure are analyzed. It has proved that single-plunger articulated steerable rib has smaller contact area due to the angular contact with the wellbore wall, resulting in uneven contact stress distribution with the maximum stress located at the front end and a significant increase at the crater of the steerable rib; rock mechanical parameters (elastic modulus, cohesion and internal friction angle) of wellbore wall have enormous influences on the wellbore wall deformation and failure. If the wellbore wall is soft, single-plunger articulated steerable rib will fall into the wellbore wall, and the immersion depth increases approximately linearly with the loading time; the risk of steerable rib falling into the wellbore wall can be reduced by appropriately reducing the pushing force or increasing the curvature radius of the steerable rib.

Keywords

• rotary steerable drilling system
• static push-the-bit
• soft formation
• wellbore wall failure
• influencing factor
• finite element simulation