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[Objective] In recent years, high-yield gas wells, such as those in eastern Sichuan, Tarim Oilfield, and Dongfang Gas in the South China Sea, have been increasingly common. However, these wells are not without their challenges. The production pipe string of Sangao gas wells is prone to vibration failure due to the impact of high-speed gas. Taking the Kuqa high-pressure gas area of the Tarim Oilfield as an example, 19 failure incidents have been recorded out of 15 wells, resulting in huge economic property losses and, regrettably, casualties. The primary cause of these failures has been identified as the excessive dynamic load caused by pipe string vibration. Therefore, understanding the vibration characteristics of the production pipe string has become a crucial study area. The production string in oil and gas wells possesses its unique characteristics. Its large slenderness ratio results in a very low overall stiffness, which is difficult to simulate in a typical small experimental system. [Methods] In this study, we established a test bench for large production string evaluation. We developed an extensive, elongated string model using Polyethylene pipe to replicate the vibration characteristics of the production string under high-speed fluid impact. [Results] The experimental results show that the production string in Sangao gas wells vibrates at a constant frequency under the influence of a high-speed fluid. The vibration amplitude is most pronounced in the middle and bottom parts of the string. It was also observed that an increase in gas yield correlates with an increase in the severity of the pipe column's vibration. An effective method of curtailing this vibration amplitude involves increasing the wall thickness of the tubing. However, it is important to note that while this may reduce the tubing amplitude, it does not change the vibration frequency of the tubing string. The packer installation position also plays a pivotal role in vibration suppression. If the packer is installed too high or too low, it fails to effectively suppress vibration. The optimal placement for a single packer has been found to be at the 8/10 position of the string, where it can efficiently suppress vibration. This paper further delves into the analysis of displacement, frequency, and vibration characteristics of simulated tubing when subjected to a high-speed fluid within the tubes. [Conclusions] This study further explores the effects of pipe wall thickness, gas yield, and packer setting positions on the vibration characteristics of simulated tubing. The following conclusions were drawn from the research. When the fluid Reynolds number within the tube reaches 21 430, the simulated tubing presents a second-order vibration mode. This results in a substantial amplitude in the middle and bottom sections of the simulated tubing, which are prone to contact and collision with the casing wall, potentially resulting in pipe string failure. The wall thickness of the tubing exerts little effect on the vibration frequency of the simulated tubing. However, it significantly affects the vibration amplitude. The thicker the tubing, the smaller the vibration amplitude of the simulated tubing. Therefore, tubing vibration can be effectively suppressed by increasing tubing thickness during the actual production process. The larger the gas production, the greater the frequency and amplitude of the simulated tubing vibration. When gas production is excessively large, the tubing is likely to collide severely with the casing wall, thereby increasing the risk of tubing failure. Therefore, it is crucial in the actual production process to determine the daily gas output reasonably, keeping in mind the bearing limit of the tubing. Packers suppress string vibration by limiting the lateral displacement of the string. Installing multiple packers proves to be more effective than a single packer in suppressing vibration. [ABSTRACT FROM AUTHOR] |
