Experimental and Modeling Study on the Master Mechanism of BHA Movement States

Lateral vibration of BHA observably disturbs drilling efficiency of downhole tools and even leads to downhole accident. To research the master factors and formation mechanism of lateral movement states when rotary drilling, the indoor experiment and numerical simulation are conducted. An indoor experimental device was designed and built, and a systematical indoor experiment were carried out to analyze the effects of different factors on movement states and motion laws. Meanwhile, a new drill-string dynamics model was derived, the occurrence mechanism of movement states was studied in vertical sections. The results show that the movement states contain forward whirling, irregular movement, and backward whirling in slightly-deviated sections, and circular arc swing in highly-deviated sections. Moreover, well inclination, rotational speed and frictional coefficient have prominent effects on movement states. In addition, a special phenomenon is found and explained in the experiment. Finally, it founds that drill-string in vertical sections should operate in the movement state with minimum output power, and operate in the movement state with minimum input power of external force during steady motion. Therefore, the principle of minimum energy consumption and minimum work consumption can be used to explain the master mechanism of movement states. The research can lay a theory basis to predict, identify and control movement states to relieve lateral vibration and raise drilling efficiency.