Abstract
NGH (natural gas hydrate) is a sort of green energy with huge reserves. When drilling and exploiting NGH, the complex drilling environment will aggravate the vibration of the drill string, which will destroy the stability of the NGH reservoir and make it decompose to produce a large amount of gas. Gas flows into the annular with the drilling fluid, filling the annular with a gas−liquid two-phase flow with a complex variation in the characteristic parameters of the pipe flow. The mixed gas−liquid annular flow will make the drill string vibration more complex and intense. In this study, the nonlinear mathematical model of the drill string lateral vibration is established by considering the influence of the internal and external fluids, gravity, and the bottom axial force on the lateral vibration of the drill string. The effect of the annular fluid velocity and gas content on the lateral vibration of the drill string was studied through experiments and numerical simulations. This study found that, with an increase in annular fluid velocity and gas content, the stability of the drill string is weakened, and the lateral vibration is intensified, so the effect of the annular fluid velocity on the lateral vibration of drill string is greater than that of the annular gas content.