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

Abstract

Natural gas hydrate (NGH) is a kind of new type green energy source with giant reserves which has been thought of highly by energy explorers in the world. However, NGH breaks down to produce some natural gas that enters the annulus and flows together with the drilling fluid. The gas-liquid two-phase flow can have an impact on the work of the drill string. Therefore, it is important to study gas-liquid two-phase flow in the annulus on the dynamic characteristics of the drill string. In this article, taking a single drill string as the research object, a fluid-structure coupled finite element mathematical model of two-phase flow in the annulus and drill string is established based on computational fluid dynamics and computational structural dynamics theory. The finite element numerical simulation method is used to analyze the influence of drilling fluid and natural gas in the annulus on the dynamic characteristics of the drill string. The simulation analysis shows the following: (1) The motion of drilling fluid or natural gas in the annulus will reduce the natural frequency of the drill string, and the drilling fluid has a greater impact on the natural frequency of the drill string. (2) When single-phase drilling fluid flows in the annulus, the displacement peak in different directions, maximum equivalent stress, and strain of the drill string increase with the increase of the drilling fluid flow velocity or pressure, and the drilling fluid pressure has a more significant effect. (3) When the gas-liquid two-phase fluid flows in the annulus, the displacement peak, maximum equivalent stress, velocity amplitude, and acceleration amplitude of the drill string all increase with the natural gas flow velocity and natural gas content increase, and the natural gas flow velocity has a more significant effect.

Dynamic Behavior Analysis of Drilling String in Horizontal Section of Deep-Sea Gas Well

“…Drill string vibration refers to the unstable movement of the drill string during drilling, which may be caused by the uneven friction between the drill string and the wall or the imbalance of the drill string itself. Drill string vibration can also damage drilling tools and wellbore equipment, increasing drilling costs [8] .…”

Development of a software module for modeling drill string displacements

“…The authors derived the additional mass coefficient for each of the considered fluids and revealed that the drilling fluid reduces the drill string vibration frequency. Wang B. et al [7] studied the impact of an annular gas-liquid flow on the drill string dynamic characteristics. The authors derived a fluid-structure coupled mathematical model of the two-phase flow and drill string in the annulus by using the Galerkin finite element method and revealed that the drilling fluid and natural gas reduce the natural frequency of the drill string and increase the mode shape vibration amplitude.…”