Investigation Of Droplet Characteristics And Pressure Drop In Oil-water Dispersed Flows

Oil-gas-water multiphase flows occur frequently in petroleum industry. So far there areno mature theoretical models due to its complexity. The current research findings havelimitations. The knowledge of oil-water is the basis of research on oil-gas-water. Dispersedflow, as an important pattern of oil-water flow, is characterized by the flow where one phaseis dispersed in the other continuous phase. The interfacial concentration, quantity, size anddistribution of drops, have great impact on apparent viscosity and pressure gradient. Thedesign of oil-water separator is also dependent on drop size and distribution. Therefore, anaccurate model of oil-water flow is significant.The size and distribution of drops and pressure gradient were studied experimentally indispersed oil-water pipeline flows using four kinds of oil and water as experimental materials.Experiments were conducted on a temperature controlled two phase flow loop and amultiphase flow loop. An isokinetic sampling device was made for the experiments. Data ondrop size was obtained using high speed camera, laser particle size analyzer and microscope.Two different measurement methods, online and sampling measuring, were conducted. Oilwater interfacial microcosmic character and its effect on flow behavior were studied underdifferent flow rates, temperatures and dispersed phase volume fractions. Data on drop sizedistribution formed both in w/o and o/w dispersions show that the Rosin-Rammler andFrechet function were found to fit satisfactorily the experimental data, and under someoperating conditions Frechet function was better. However, Normal function could notdescribe the experimental drop size distributions well. The results show that the size anddistribution of drops are affected by many factors including oil physical properties, flowcharacteristics, surfactants, shearing of pump and pipeline, etc. The drop size increases as the temperature and phase fraction rises, but decreases as the flow rate and viscosity rises.Surfactants have a significant impact on drop size distribution and stability.The drop formation mechanism was studied experimentally and theoretically. Data showthat drop break-up time is8-20ms, and the frequency is about25~62.5Hz, while thecoalescence time is about2ms. The balance time when oil and water went into the pipeseparately was longer than together.A predictive model for calculating SMD in oil-water dispersed flows was developed,based on the study of a balance between the turbulent kinetic energy and the surface energy ofdispersed liquid drops, the approximate equal relations of the radial velocity fluctuation andthe friction velocity, and the shear stress of the pump. From comparison with experimentaldata, the model predictions are accurate. Model results show that drop size is10-100timeslarger than that with pump. Pump plays a significant role in forming drop size distributions.Experiments have been performed in two different pipe loops. The comparison showsthat different flow patterns were formed under two injection modes. When oil and water wentinto the pipe together, dispersed flow range was wider. Phase distribution of oil-water pipeflow was calculated by using FLUENT software, which shows that phase distribution is moresymmetrical as flow rate rises. Pressure gradient is also affected by many factors including oilfraction, flow rate, temperature, viscosity, and surfactants, etc.Oil water interfacial microcosmic characteristics have great impact on macroscopiccharacteristics such as apparent viscosity and pressure gradient. As the interface concentrationand interfacial energy rises, pressure gradient increases. A correlation was developed forcalculating apparent viscosity, which has not, to the author’s knowledge, been mentionedbefore and has certain significance both in modeling oil-water flow and in practice. Fromcomparison with experimental data, the predictions are accurate.