# Study on Flow Characteristics of Venturi Accelerated Vortex Drainage Tool in Horizontal Gas Well
## 1 Introduction  
The application of horizontal wells can achieve a high level of production with fewer wells; these have become the main exploitation method used in deep natural gas fields. However, the liquid accumulation in the wellbore of horizontal wells leads to a decrease in gas production, which is a key issue faced by various large gas fields. In view of horizontal well drainage gas recovery, numerous scholars have carried out relevant research. The vortex tool has been used more and more for drainage gas recovery based on the swirling flow mechanism. When the vortex tool is used, a gas-liquid two-phase fluid flow occurs through it to generate tangential velocity and form the swirling flow. Due to the centrifugal force, the liquid phase with a higher density flows along the wall, and the gas phase with a lower density flows in the center of the tube, which improves the effect of the drainage. Many scholars have studied the working mechanism of vortex tools and verified their effectiveness. [PERSON] et al. [1] analyzed the drainage of gas wells. The radial distribution ofthe liquid phase and the gas-liquid flow pattern have been investigated at the wellhead. The influence of the gas and liquid production capacity of gas wells and the main geometric parameters of vortex tools on the flow field were obtained. In order to evaluate the drainage effect of the internal vortex tool, [PERSON] et al. [2] simulated the flow field and the liquid-carrying process of the gas-liquid two-phase fluid in the wellbore before and after the internal vortex tool was attached to the bottom of the tubing. The experimental results show that the internal vortex tool can effectively improve the liquid-carrying capacity and the flow pattern of the wellbore fluid and reduce the pressure drop. At the same time, the gas-liquid two-phase flow pattern and the pressure drop under different flow parameters were studied by numerical simulation. Finally, the experimental results were compared with the numerical simulation results, and it was found that the error of the pressure drop is within 10%. [PERSON] et al. [3] carried out a numerical simulation of three internal swirling tools and analyzed the drainage recovery efficiency and the vortex characteristics of the swirling flow field downstream of the tools. By the energy efficiency analysis of the three structures, it was found that the three-leaf spiral tube is more suitable to apply during the initial stage of drainage, while the internal vortex tube is more conducive during the stable stage of drainage. The feasibility of the internal swirling tool in horizontal gas wells is demonstrated. [PERSON] et al. [4] analyzed the physical process of eddy current tools for the drainage gas recovery, established a numerical simulation model, and developed the optimized design software. According to the eddy flow mechanism, the geometric parameters of eddy current tools, which are more suitable for gas well reservoirs, were determined, and the positioning depth of the vortex tool was calculated according to the Bernoulli equation. The field test results show that the application of eddy current tools resulted in effective gas-liquid separation, which is beneficial to increase the production of natural gas. [PERSON] [5,6] analyzed the forces of liquid droplets in the swirling flow field of wellbores on the basis of two-phase fluid dynamics theories, establishing the motion equations of fluid droplets along axial and radical directions. The formula for calculating the optimal helical angle of vortex tools was established. [PERSON] [7] established a mechanistic model for the prediction of the swirling annular two-phase flow behavior downstream of the vortex tool, which has a guiding significance for the optimization design and field application of vortex tools. The structural parameters of vortex tools are crucial for their drainage and gas extraction effectiveness. [PERSON] et al. [5], based on two-phase flow theory, analyzed the forces acting on droplets in the rotating flow field of the wellbore.