Study On Effective Viscosity Of CO₂ Dissolved Crude Oil And Crude Oil-water Mixture Systems

As CO₂ flooding technology is more and more applied in the process of oil exploitation,CO₂ will inevitably have profound impact on effective viscosity of oil flow.As the oil-water system is usually a mixture system composed by emulsion and free water,and there are still not enough researches and effective means about this presently,it is very necessary to study the effective viscosity of mixture system of CO₂ dissolved crude oil-water system and designed effective apparatus.So this paper firstly designed the pressurized emulsification and stirring-viscometric apparatus by stirring-viscometric theory,and devised the experiments at the basis of such apparatus,to dissolve CO₂ into heavy oil under different conditions,supplemented by dissolving N₂ into heavy oil to analyse CO₂'s effect on effective viscosity of crude oil;then combined with the dehydration ratio measuring device and Tracker-H interface rheometer to study CO₂'s impact on emulsification of crude oil,and further study the effective viscosity of mixture system under different pressure,temperature,mean shear rate and water volume fraction.The changes of effective viscosity of CO₂ dissolved heavy oil mixture showed that effective viscosity of heavy oil reduced exponentially with the increase of pressure;the precipitated asphaltenes caused by the dissolution of CO₂ formed suspended solid particles in heavy oil,thereby the CO₂ dissolved heavy oil mixture showed shear-thinning behavior;the viscosity reducing rate of CO₂ dissolved heavy oil mixture increased with decreasing temperature,while the trend for dissolved N₂ heavy oil mixture was just the opposite.The stability of CO₂ dissolved oil-water mixture system with decreased with the increase of pressure and water volume fraction.According to interfacial properties experiment,the stability of such mixture system had corresponding relationship with dilatational viscoelasticity of droplet's film,and improved with the increase of elastic modulus.As the mixture could keep homogeneous when been fully stirred,the following experiments considered the mixture of dissolved CO₂ crude oil-water as homogeneous mixture system.The results of experiments for CO₂ dissolved crude oil-water system showed that effective viscosity of mixture system reduced with the increase of pressure,temperature and mean shear rate and decrease of water volume fraction.For Dahun mixture system,the effective viscosity was already considerably reduced when CO₂ was pressurized to 4 MPa,and temperature's increase would have less influence on effective viscosity under higher pressure;and effective viscosity of mixture system with higher water volume fraction would be more sensitive to the temperature when CO₂dissolution pressure was lower than 4 MPa;as mean shear rate increased,the curve of viscosity reduction of mixture system gradually became gentle;and when the water volume fraction of mixture system was 0.4 and 0.6,its effective viscosity would greatly increase with higher water volume fraction.For Changqing mixture system,its viscosity reduction with increase of CO₂ dissolution pressure was strengthened when the pressure was higher than 1.5 MPa;as the mean shear rate increased,the lower water volume fraction of mixture system was,the smaller the extent of viscosity reduction was;while compared to Dahun mixture system,its curve of viscosity reduction with mean shear rate was more steep;and its effective viscosity tended to increase linearly with the increase of water volume fraction.