Effect of Annular Gas-Liquid Two-Phase Flow on Dynamic Characteristics of Drill String

Table 3

The natural frequency of the drilling string under fluid-structure coupling.

Order	Natural frequency (Hz)			Change rate
	Uncoupled	Fluid-solid coupling	Gas-liquid-solid coupling	Former two (%)	Later two (%)
1	8.904	8.026	8.028	9.86	0.02
2	8.905	8.026	8.028	9.87	0.02
3	24.471	23.659	23.668	3.32	0.04
4	24.471	23.658	23.667	3.32	0.04
5	47.783	46.986	47.008	1.67	0.05
6	47.783	46.987	47.009	1.67	0.05