Abstract
Liquid unloading is a very common and important issue in horizontal gas wells, and the presence of curve sections increases the complexity of the phenomenon and its study. Liquid loading in a gas well will sharply reduce production, therefore, the liquid-unloading onset of different curved pipes is essential to gas production. In this work, liquid-unloading onset experiments were conducted in curved pipes with different curvatures. Then, the critical gas velocityVsgCRcan be determined according to the measured pressure gradients, liquid holdup, and liquid film reversal. This work analyzes the factors which will lead to the liquid unloading and explores the trend of the pipe curvature’s influence on the liquid unloading under laboratory conditions. The experimental results show that the critical gas velocity rises with the increase of pipe curvature, the increase is mainly due to the centrifugal force. The present work also compares the predicted results of the OLGA model and Beggs–Brill model with experimental data. The comparison results indicate that both models fit relatively well to the experimental data at the low superficial gas velocity, and both models have poor performance at high superficial gas velocity. The OLGA model fits the experimental data better than the Beggs–Brill model at high superficial gas velocity. The error analysis shows that most of the predicted data is not in good agreement with experimental data. Some errors between experimental data and calculation results are out of the range of 50%.
Highlights
Liquid loading/unloading in gas wells is always an important issue in the oil/gas industry, which may prevent gas production and even shut down the gas well, which will cause economic losses
During the gas production process, the liquid phase exists in the well as liquid film and droplets which move along the tube, the gas phase exists in the well as gas core which carries the liquid droplets at the center of the tube
The experimental results showed that the 2-in ID pipe has the largest critical gas velocity, and it decreases as the pipe ID increases
Summary
Liquid loading/unloading in gas wells is always an important issue in the oil/gas industry, which may prevent gas production and even shut down the gas well, which will cause economic losses. Van’t Westende et al (2007) conducted some liquid-loading experiments of dispersed phase with the annular flow pattern in a vertical tube of 5 cm ID (Inner Diameter) They used PDA (Phase Doppler Anemometry) to measure the size and velocity of liquid drops entrained in the gas core. Waltrich et al (2015) conducted experiments to study the initiation of liquid-loading in a 2-in ID and 42 m long vertical pipe They recorded pressure, temperature, and liquid holdup to analyze the liquid film reversal conditions and compared with previous models. The experimental results showed that the 2-in ID pipe has the largest critical gas velocity, and it decreases as the pipe ID increases They found that the initiation of liquid film reversal is inconsistent with previous studies in the 2-in ID pipe case. The predicted results of the OLGA model and Beggs–Brill model were compared with experimental data to verify the models’ accuracy of the curved pipe cases
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