The Effect of Water Dissolution on Oil Viscosity
- C.A. Glandt (Shell Development Co.,) | W.G. Chapman (Rice U.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- February 1995
- Document Type
- Journal Paper
- 59 - 64
- 1995. Society of Petroleum Engineers
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- 452 since 2007
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At temperatures above 150 degrees C water dissolution in crude oil becomessignificant. Water solubilities in heavy crudes am about 40 mole percent at 250degrees C. Dissolved water acts as a low viscosity solvent reducing the oilphase viscosity. This phenomenon has been considered in thermal recoverysimulations but has never been substance in this work the effect of water onviscosity was measured for four crude samples with API gravities ranging from14.2 to 5.3. At the highest experimental temperature of 286 degrees Cviscosities of water saturated samples were about one half of the water-freecounterparts. The viscosity reduction, although quite significant, was not aspronounced as the drop estimated by viscosity miles used for hydrocarbonsystems. While a log mixing rule or a 1/4 power mixing rule overestimated theviscosity effects, a mole fraction weighted average of the oil and waterviscosities was found to match the experimental data. One possible explanationfor the failure of the log mixing rule is that the water dissolved in the oilexists not as monomers but as hydrogen bonded dusters. When the mole fractionof water clusters, calculated from a statistical mechanics based theory, isused in the log mixing rule, we find good agreement with experiment.
SUMMARY AND CONCLUSIONS
At temperatures above 150 degrees C water dissolution in crude oils becomesignificant. Water solubilities in heavy crudes are about 40 mole percent at250 degrees C.
Dissolved water acts as a low viscosity solvent reducing the oil phaseviscosity. This phenomenon has been considered in thermal recovery simulationsbut has never been substantiated.
In this work the effect of water on viscosity was measured for two heavyoils, Huntington Beach (API gravity = 14.2) and Cloalinga Etchegoin (APIgravity = 10.5), and two tars, West Cat Canyon (API gravity = 5.3) and PeaceRiver (API gravity 6.7).
At the highest experimental temperature of 286 degrees C viscosities ofwater-saturated samples were about one half of the water-free counterparts. Theviscosity reduction, although quite significant, is not as pronounced as thedrop estimated by viscosity mixing rules used in simulation work in thepast.
A mole-fraction weighted average of the oil and water viscosity was found tomatch the experimental data. Dissolved water exists on average as hydrogenbonded clusters. The log mixing rule matches the experimental data when themole fraction of water clusters is used.
Water dissolution in an oleic phase has been reported. The effect isnegligible in crude oils at temperatures below 150 degrees C and becomes verypronounced (more than 60% mole fraction) as the temperature riser, above 280degrees C.
The effect of dissolved water on the oleic phase viscosity has never beenreported. Its potential impact has been estimated based on viscosity mixingrules typically used in hydrocarbon systems which predict very significantviscosity reductions due to water dissolution at high temperature. Thesepredictions lack experimental support, however.
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