Multiphase Flow Of Water-in-Oil Emulsion By Considering Hydrate Transition

Hydrate has become one of the largest issues of the flow assurance in deep-water and ultra deep-water oil-gas production and transportation.To decrease the capital expenditure on dealing with hydrate,hydrate prevent strategy has been shifted from complete inhibition to risk management.Understanding the hydrate formation/dissociation characteristics and the resulting changes on system flow behavior are very important to the risk management.This study aims at water-in-oil emulsion and investigates the basic aspects included in the physical model proposed for describing the hydrate formation process of water-in-oil emulsion by Turner.Based on the droplet formation theory,three kinds of emulsion systems with different breakup mechanisms were settled,and the effects of dispersed phase concentration,rotor speed,and dispersed phase viscosity on drop size distribution and relative sizes were studied.The models for describing drop size distribution were optimized,and the linear relationship between the Sauter drop size and maximum drop size is valid for both monomodal and bimodal drop size distribution.Based on the quantitative analysis of relative sizes,two systems’ results were fitted by existing models with satisfactory accuracy.A modified version of Calabrese’ model has been developed for combining the effects of dispersed phase content and viscosity,which represents the experimental data well.The rheology of water-in-oil emulsion was studied by using two kinds of emulsion preparation methods.According to the rheological characteristics of emulsions,the whole rheological behavior was divided into Newtonian regime and non-Newtonian regime,and the effects of dispersed phase concentration and drop size on emulsion rheology were investigated,respectively.Furthermore,the existing theoretical models were compared and optimized by the experimental data.Based on the flocculation theory,a correlation was developed for determining the cluster size of water-in-oil emulsions and the apparent viscosity subsequently by combining Mooney and Mühle model.The correlation can predict the shear-thinning behavior quite well.Empirical graphic method,Chen-Guo model,CSMGem and Multiflash were evaluated by using one-component,two-component and three-component hydrate equilibrium data.Based on the introduction of exiting hydrate kinetic models,the state-of-the-art of hydrate kinetic was understood,and particularly the formation process and describing model for hydrate formation in water-in-oil system were presented.The effects of ice and hydrate formation/dissociation on moderate to high water cut water-in-oil emulsion stability have been investigated by using the differential scanning calorimetry and Bottle test.The effects of NaCl and Arquad 2HT-75 were also investigated.Overall,the comparison between in-situ high pressure differential scanning calorimetry measurements and the autoclave cell tests indicates that the differential scanning calorimetry test is an effective and simple method for representing the shut-in conditions in offshore pipelines.The measurements of hydrate-droplet interaction force were successfully implemented by modifying the micromechanical force apparatus,and the effects of contact time,subcooling,contact area,mineral oil and Span 80 on interaction force were studied.The evolutions of liquid bridge geometry,liquid-solid contact angles,interaction force and rupture point during the measurement were predicted by theothiral model,which are in agreement with the experimental data well.Furthermore,the cohesion force between hydrate particles was measured and the effect of hydrate particle surface roughness on interaction force was discussed.According to the quantitative analysis and evaluation of the basic aspects,the theoretical model describing the flow behavior of water-in-oil emulsion by considering hydrate transition was developed by utilizing the theory of heat transfer and multiphase flow.The numerical simulation results show that the model cannot only predict the hydrate formation region,but also the quantitative influence of hydrate formation/dissociation on system flow behavior.Sensitivity analysis shows that lower liquid output,higher water content and cohesion force can result in higher hydrate slurry viscosity,and consequently a higher hydrate plug risk in pipeline.