Experimental investigation on pressure fluctuation characteristics of gas-liquid two-phase flow in hybrid tower riser

In order to investigate the pressure fluctuation characteristics of gas-liquid two-phase flow in the hybrid tower riser system in deep-water oil and gas fields, an indoor test was carried out in this paper to analyze the varying characteristics, amplitude fluctuation and other characteristics of pressure in different flow patterns. In the test, six flow patterns were identified. Each flow pattern is corresponding to the specific pressure fluctuating pattern, and the maximum fluctuating amplitude occurs in the transitional flow pattern II during the transform from the severe slugging flow to stable flow. It is shown that the pressure fluctuation amplitude increases firstly and then decreases with the increase of the superficial gas velocity by analyzing the maximum and minimum pressures at the bottom of the riser, and the change of flow pattern is more sensitive to gas velocity than liquid velocity. The pressure distribution characteristics under different flow patterns were obtained based on the statistical analysis of Probability Density Function (PDF) and Cumulative Distribution Function (CDF). In the working condition of severe slugging, the PDF curve for the pressure at the bottom of the downward inclined pipeline presents the remarkable characteristic of single peak in the high pressure zone, that in the transitional flow pattern has two equal peaks at the right and the left sides in the form of high in both ends and low in the middle, and that in the stable flow pattern has more peaks with a narrow range of pressure. The turning point of CDF in the high pressure zone corresponds to the peak of the PDF curve. The peaks of the PDF curves for the pressure at the bottom of the jumper pipe are in the range of low pressure zone and they are high in the middle and low in both ends. The PDF curves present two or three peaks in the working condition of severe slugging and a single symmetrical peak in the pattern of stable flow. In conclusion, combined with PDF and CDF curves of pipeline pressure, flow patterns can be discriminated and analyzed, and the system pressure probability distribution characteristics can be attained intuitively, so as to provide the important basis for the fatigue damage and safety assessment of pipelines.