Abstract
Vortex tool is a new technique for the liquid unloading in gas wells. But it lacks a mathematical model to describe and predict the effect of vortex tools. In the present work, according to the axial, radial and circumferential momentum balance of the gas phase and liquid phase, the governing equations of vortex flow model have been established. Then thickness of liquid film and gas and liquid vortex flow intensity as well as the pressure drop gradient can be calculated. The calculation results and the previous experiments indicate that the pressure drop of the gas–liquid flow can be reduced by 5% ~ 25% with the vortex tool, and the vortex flow model has an average relative difference of 6.01%. The model results show that there are two mechanisms for reducing the pressure drop under the vortex flow condition. In addition, the research results show that vortex tools with bigger helical angle will lead to higher vortex flow intensity. The decay rate of vortex flow intensity decreases along the pipe as liquid velocity increases and the vortex flow working distance can be calculated by the vortex intensity gradient and initial vortex flow intensity.
Highlights
Liquid loading is one of the significant issues needed to be overcome in gas-well production
The result shows that g > 1 and szi ! sgf, which means under the effect of vortex tool, the drag force on liquid increases, and the thickness of liquid film decreases calculated by equation (13), which will lead to the decrease of gravitational pressure drop
The vortex tool #1 has the smallest helical angle, according to equation (43), which leads to the biggest vortex flow intensity; and based on equation (31), it has the biggest interfacial force, so liquid holdup will decrease at low gas superficial velocity, while increase friction at high gas superficial velocity
Summary
Liquid loading is one of the significant issues needed to be overcome in gas-well production. Mingaleeva (2002) found that the minimum pressure loss can be obtained when the gas– liquid fluid moves upward in vortex flow regime Based on this theory, the downhole vortex tool in gas well was designed to decrease the pressure drop along the wellbore. Surendra et al (2009) carried out a numerical simulation study on gas–liquid two phase flow process with the vortex tool. Liu and Sun (2017) studied on the vortex tool with numerical method and conducted laboratory test and downhole test on geometrical parameters of the vortex tool They found the preferred helical angles are 50° and 55°. Like other downhole liquid-unloading tools, the vortex tool cannot provide energy for gas–liquid two phase flow, but it can increase the efficiency of formation energy by improving flow conditions. The present work mainly focused on building a theoretical vortex flow model which is based on the two-phase flow theory and experiments were conducted to validate the vortex model
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