Introduction Heavy crude oils continue to be a challenge to dehydrate for the Oil & Gas Industry.
The traditional remedy to the reduced oil / water density difference, higher crude oil viscosity and often smaller water droplets due to heavy crude oil production techniques, often leads to high operating temperatures, fouling, production upsets, very large treaters and dosage of large volumes of demulsifier chemicals. This leads to both higher OPEX as well as higher CAPEX.
Other challenges include higher crude oil conductivity and increased crude oil emulsion viscosity due to higher water cuts. Typically crude oil dehydration vessels use heat, retention time and AC type electrostatic dehydration technology. The AC technology provides limited voltage gradients and is not efficient for treating conductive crude oils, leading to the use of very large vessels and power units, and the use of lower voltage gradients.
The use of combined AC / DC electrostatic technologies provides more efficient bulk water removal combined with higher removal efficiency of small water droplets from the crude oil. Further improvements include modulated electrostatic fields, improved electrode configurations as well as improved fluid distribution inside the electrostatic treaters.
More efficient dehydration means smaller treaters, lower operating temperatures and use of less demulsifier chemicals.
This paper describes new enhanced electrostatic dehydration technologies, efficient test methods for optimized usage of production chemicals and selection of electrostatic technologies, including case studies
Heavy Oil Properties. Heavy crude oil normally refers to crude oils with an API gravity of 20 or less. There are also sub-definitions for very heavy oil ( below API 14° ) extra heavy oil ( API 11° and below ). Heavy oils also tend to be blacker in color, due to the higher Carbon / Hydrogen ratio.
Some of the characteristic properties for heavy crude oil: - High density ( 934 kg/m3 @ 20°C and higher ) - High viscosity - Lower salinity of the formation water ( produced water ) - Higher solids loadings - Often higher crude oil conductivity - Lower Gas / Oil ratio
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