Stick-Slip and Bit-Bounce Interaction in Oil-Well Drillstrings

TLDR

Drillstring vibrations, especially stick‑slip and bit‑bounce, damage oil‑well equipment and operations, making their control essential. Because the conditions causing these vibrations are variable and uncertain, simple guidelines or rotary‑table controls cannot eliminate them. The authors use a simple dynamic model to simulate how varying operating conditions affect stick‑slip and bit‑bounce interactions. The study shows that bit‑speed and formation stiffness dominate the dynamic response, and that an additional axial‑motion controller can suppress both stick‑slip and bit‑bounce, potentially enabling smooth drilling over a wide range of conditions.

Abstract

Drillstring vibrations and in particular stick-slip and bit-bounce are detrimental to oil-well drilling operations. Controlling these vibrations is essential because they may cause equipment failures and damage to the oil-well. A simple model that adequately captures the dynamics is used to simulate the effects of varying operating conditions on stick-slip and bit-bounce interactions. It is shown that the conditions at the bit/formation interface, such as bit speed and formation stiffness, are major factors in shaping the dynamic response. Due to the varying and uncertain nature of these conditions, simple operational guidelines or active rotary table control strategies are not sufficient to eliminate both stick-slip and bit-bounce. It is demonstrated that an additional active controller for the axial motion can be effective in suppressing both stick-slip and bit-bounce. It is anticipated that if the proposed approach is implemented, smooth drilling will be possible for a wide range of conditions.