| At present,vertical pipes are one of the frequently encountered structures in deep-sea oil fields,which are widely used in platform riser and well bore.The frequently encountered flow patterns of vertical pipe are bubble flow,slug flow,churn flow and annular flow.The flow characteristics of multiphase flow in pipelines are different under different flow patterns.Monitoring the flow in vertical pipe timely can ensure deep sea oil field exploitation and safe and economical transportation of long distance pipeline.Acoustic emission(AE)measurement method has attracted wide attention,due to its wide range of sound frequency,and non-invasive characteristics.As a result,the study of acoustic emission measurement for oil and gas industry is significant.Three sets of experimental rigs were designed and established in this paper,including the experimental devices of continuously bubbles released from a single nozzle or multiple nozzles,and the experimental devices of gas-liquid two phase flow in vertical rising pipe.A real time acquisition and calculate program was developed to record the AE signal and compute the AE parameters simultaneously.High speed camera and conductance probe were used synchronously,by which the feasibility and accuracy of acoustic emission detection for multiphase flow are verified.The AE signal of bubble generation and bubble rising motion was enhanced with the increment of the gas velocity at the orifice,which was found in the experiment in a single orifice nozzle.Besides,the results show that AE signals of each category have a certain degree of similarity in time frequency analysis based on k-means clustering analysis.Also the AE signals of moving bubbles in their rising stages can be efficiently studied combined with images and the flow patterns of moving bubbles can be identified,including bubble oscillation,breakup,coalescence and so on.This experiment provides an effective method for the sound signal processing of multiphase flow.The AE characteristics of multi-bubble collective oscillation under different combination of nozzles was studied in the experiment of multiple nozzles.Reducing the bubble spacing or increasing the number of bubbles can improve the AE signal and increase the acoustic signal waveform parameters.The main frequency range of single bubble oscillation is 50 ~ 130 kHz.The peak frequency is 60 kHz and 130 kHz.Compared with single bubble oscillation,the frequency of multi-bubble collective oscillation is lower,and the signal in high frequency partial is weakened.The effect of surface tension on AE characteristics of multi-bubble collective oscillation was studied by changing the surface tension of experimental liquid phase with sodium dodecyl benzene sulfonate.Besides,the surface tension is reduced by adding surfactant.The intensity of acoustic emission signal is greatly reduced.In the experiment of gas-liquid of two phase flow in vertical rising pipe,the time domain characteristics and frequency domain characteristics of AE signals under four flow patterns,such as bubble flow,slug flow,churn flow and annular flow,were compared and analyzed.It was found that the flow regimes of gas-liquid flow in the vertical pipe could be efficiently indentified by the AE technique.According to the characteristics of slug flow in vertical rising pipe,AE signals were used to analyze the macroscopical flow parameters,such as frequency,velocity and length of liquid slug.Local characteristics of liquid slug including AE signal parameters of local liquid slug and probability density distribution of root mean of square of AE signal were analysed.It was vetified that the root mean square of AE signal could describe the characteristics of liquid slug.The model of gas void fraction was established by analyzing the relation of gas void fraction,root mean square and mixing velocities.Besides,the model was compared with the result synchronously measured by the double parallel conductance probes installed in the experimental test section.The result shows that AE technology has good application value in slug flow measurement. |
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