Characteristics of liquid loading with surfactant injection in hilly terrain pipeline

Abstract

Surfactant injection technology has recently been proposed as an alternative to mechanical pigging for liquid unloading from the wellhead to the surface gas gathering system. This study aimed to verify the effectiveness of the technology by experimentally evaluating the liquid loading characteristics of gas–liquid flow with a surfactant at the undeveloped and developed flow positions of the uphill test section (10°) of a hilly terrain pipeline. The inner diameter and length of the uphill test section were 50.0 mm and 16.0 m, respectively. The liquid and gas working fluids were deionized water or 250 ppm sodium dodecyl sulfate (SDS) surfactant solution and air with the superficial velocities of 0.001 to 0.010 m/s and 2.0 to 14.0 m/s. The liquid volume fraction and liquid holdup were measured using the image-quick closing valve method and wire mesh sensor method, respectively, and the liquid holdup data were visualized using the MATLAB program and Tecplot software. Owing to the effect of the surfactant, the flow range of low liquid loading increased significantly with the flow regime transition from intermittent flow to segregated flow. Because of the complex interaction between the morphology of the slug body and the foam formation, the fluctuation range and peak of liquid holdup and the liquid volume fraction decreased significantly in the intermittent flow. The liquid holdup fluctuation range and liquid volume fraction decreased to nearly zero, and a foam layer was formed and climbed up along the pipe wall in the segregated flow. The results and analyses are beneficial for improving the surfactant injection scheme and establishing a prediction model.