Investigation On Hydrodynamic Characteristics Of Extra Heavy Oil-water Two-phase Flow In Horizontal Pipes

Heavy oil is rich in colloid and asphaltene,its special qualities such as high viscosity,large density and poor liquidity leads to the difficultity in heavy oil transportation..However,Owing to the complexity of oil-water two-phase flow,the related research is quite limited,Besides,most of the present research only focus on the flow formed from light crude oil instead of the heavy crude oil.In this paper,the hydrodynamic characteristics of the extra heavy oil-water two-phase flow is studied systematically,which is of great significance for the transportation of heavy crude oil.The main contents and conclusions of research are as follows.Firstly,the flow patterns of extra heavy oil-water two-phase flow are studied.Six flow patterns are obtained in the experiment: Ew/o dispersed flow,Ew/o&w intermittent flow,Ew/o&w stratified flow,Ew/o&w semi annular flow,Ew/o&w annular flow and Ew/o&w slug flow.Furthermore,by making a flow pattern map,the effects of different parameters are analyzed.The results show that,when the viscosity of the oil is higher,the stratified flow is more simple and the intermittent flow and annular flow are much easier to form.Meanwhile,in this case,the o/w emulsion is harder to form and the water cut of phase inversion is lower.;As for the effect of temperature on the flow patterns,it first works by affecting the viscosity of the oil.Secondly,it has a positive effect on the critical conversion flow velocity from stratified flow to annular flow,which means the lower the temperature is,the lower the velocity will be.At the same time,it has to be noted that the water cut play a decisive role in determining the flow pattern and can affect the critical velocity for flow pattern conversion to some degree.The increase of velocity is proved to promote the flow pattern conversion and phase inversion.Secondly,The effects of water cut,velocity and temperature on the pressure drop of extra heavy oil-water two phase flow are studied.The results show that,with the increase of water cut,the pressure drop first increases to its peak.After that,the phase inversion occurs,and the pressure drop decreases dramatically to a small value and then keeps constant.In the whole process,the pressure drop goes up with the increase of velocity.However,when the flow approaches the phase inversion state,the increase of the velocity can accelerate the inversion,which results in the fluctuation of the pressure drop.As for the effect of the temperature,it is quite different before and after the phase inversion.Specifically,before the phase inversion,the pressure drop is sensitive to the change of the temperature.Higher the temperature is,lower the pressure drop will be.However,after the phase inversion,the pressure drop changes little with the temperature and higher the temperature is,higher the pressure drop will be.At the same time,the drop of the temperature has a positive effect on the phase inversion.Also,the phase inversion process of the extra heavy oil-water two phase flow is studied.It is interesting to find that,unlike conventional phase inversion,in this study only w/o emulsion is obtained in the whole process,without formation of o/w emulsion.Meanwhile,during the inversion process,the intermittent flow with obvious pressure drop fluctuation is obtained.Thirdly,This paper also do some research on the droplet diameter distribution in Ew/o dispersed flow.The results indicate that the diameter of most dispersed phase droplets is smaller than 10?m,in line with Log-Normal distribution.The effects of flow parameters on droplet diameter are also analyzed.It is found that the droplet diameter is sensitive to the change of water cut.When the flow approaches phase inversion point,the diameter reaches the peak.However,no obvious effects of velocity and temperature on the diameter are abserved.Finally,according to the experimental data,some modification on the present model is made and an effective viscosity model for this extra heavy oil-water two phase flow is achieved,which is proved to work well with the experimental data.