The Response Characteristics Of Turbine Flowmeter Under Complex Multiphase Flow Conditions

With the development of oil production towards more extreme environments, the practice of well logging faces more challenges in respect of flow measurement in com-plex pipe flows. In this study, the response performance of a small turbine flowmeter, which is widely applied for well logging, in complex flow conditions including the low flow, the viscous flow and multiphase flow, was investigated with combined experi-ments and theoretical calculations.Firstly, a theoretical model was established on the basis of the conventional Thompson-Grey model to calculate the response of a turbine flowmeter in single-phase pipe flows. Experiment of particle imaging velocimetry (PIV) was conducted to measure the inlet velocity profile of a turbine flowmeter, which serves as an input of the theoretical model. Compared with previous idealized inlet profiles, the results with actual PIV measured velocity profile agree better with the real cases. Considering the real inlet velocity pro-file, the response performance of two different cascade designs was compared with the theoretical model. One type is flat and the other is twisted and hence well suits the inlet velocity profile. The turbine with twisted cascade was found exhibiting better response linearity, agility, start capability, and superior application robustness. A dimensionless quantity, Qe, was proposed to characterize the deviation of the cascade suited veloc-ity profile from the actual inlet flow profile. Decrease of Qe leads to a faster turbine response and better robustness. The parameter was found to be effective in evaluating the fitness of the cascade design with the flow profile as well as the performance of the whole flowmeter.Secondly, the performance of a turbine flowmeter at low flow rate conditions and highly viscous flow conditions is experimentally investigated. A steady low flow pipe system was built for the investigation. The speed and behavior details of the turbine are captured by a high-speed video camera. It was found that the rotation of the turbine generally fluctuates periodically due to eccentricity of the rotor, when the flow rate ap-proaches the start-up limit, and that along with the rise of the flow rate, the fluctuation decreases. For better understanding of the turbine response in such extreme cases, a further extension to the turbine performance model was introduced to address the effect of eccentricity and to catch the transient feature of unsteady responses. With the help of the theoretical model and corresponding calibration experiments, several suggestions for improving the response performance of a turbine flowmeter at low flow conditions were proposed. Furthermore, the response performance of a turbine flowmeter in Poly-acrylamide (PAM) solutions with varied concentrations was tested, which indicated that the start-up flow rate and the rotational instability of the same flowmeter decrease with the fluid viscosity. Below the linear response limit, the K-factor of the flowmeter in varied PAM solutions falls into a general dependence on the local Reynolds number.Thirdly, the responses of turbine flowmeters in a vertical air-water flow and hori-zontal oil-water flow were experimentally investigated. The two-phase flow field and the transient response of the turbine were mainly captured by direct high speed photog-raphy. For air-water flow, in addition, the cross-sectional phase distribution was also recorded by arrayed ERT. The experiment revealed that the rotation rate of the turbine drops when air intrudes the rotor, and that the fluctuation amplitude of the rotational fre-quency becomes less pronounced with the increase of the water flow velocity. Another extension to the turbine performance model was carried out to involve the non-steady two-phase effect. It was found that the extended model may well depict the response of the turbine flowmeter in two-phase vertical flow as long as the ERT data was built in. For oil-water flow, the turbine response was found to shift slightly from that in pure wa-ter, which, however, becomes much more considerable in stratified flow. A theoretical modeling of the response of the turbine meter in steady stratified flow was also realized, and the established model was found to be able to predict some important features of meter response in reality.Besides all, the drop coalescence phenomenon, which may influence the transi-tion of flow patterns, was paid special attention to in this study. A novel method that allows high speed shadow graphic visualization of the phenomenon through top view was proposed and performed, by which the formation and the early-stage expansion of the liquid bridge were fully observed. An examination of the growth of the neck radius shows a good similarity with previous ultra-electronical researches of ILV and inertial regime, and a tiny displacement of the liquid bridge was detected when the crossover occurs. The initial radius of the ambient fluid film that exists between the two approach-ing deformed drops increases with the approaching velocity of the two drops while the "coalescence" scenario converts to the "collision" scenario depending on the location of the start point of rupture.