A method for quantifying vertical stratification in crude oil emulsions by rotational viscometry

Area of Science:

• Petroleum Engineering
• Rheology
• Materials Science

Background:

• Vertical stratification in crude oil-produced water-surfactant emulsions impacts stability and handling during quiescent storage.
• Existing methods often lack quantitative, height-resolved data on the evolving mechanical state of these emulsions.

Purpose of the Study:

• To present a practical workflow for characterizing stratification and aging in emulsions using a rotational viscometer.
• To develop a quantitative index for assessing stratification magnitude and evolution over time.

Main Methods:

• Utilizing a Brookfield-type rotational viscometer under fixed conditions (spindle speed, temperature).
• Measuring apparent viscosity at predefined heights along the liquid column at scheduled aging times.
• Calculating a dimensionless Stratification Index, SI(t), based on height-dependent viscosity profiles.

Main Results:

• Generated spatiotemporal apparent viscosity maps to visualize stratification.
• The Stratification Index, SI(t), effectively quantifies stratification and its evolution.
• The method allows for direct comparison across formulations with varying absolute viscosity levels.

Conclusions:

• The described workflow offers a practical and quantitative approach to characterize emulsion stratification and aging.
• The Stratification Index provides a valuable tool for comparative screening of emulsion formulations.
• This method enhances understanding of emulsion stability and handling properties.