Abstract
Abstract
Formation of emulsions during oil production is a costly problem, both in terms of chemicals used and due to production losses. This paper discusses production and operational problems related to crude oil emulsions, and present a review that will be very useful for practicing engineers.
The first part of this paper presents why emulsions form during oil production, the types of emulsions encountered, and new methods for characterizing them. Crude oil emulsions are stabilized by rigid interfacial films that form a "skin" on water droplets and prevent the droplets from coalescing. The stability of these interfacial films, and hence the stability of the emulsions, depends on a number of factors including the heavy polar material in the crude oil (asphaltenes, resins, waxes, etc), solids (clays, scales, corrosion products, etc), temperature, drop size and drop size distribution, pH, oil and brine composition. These effects on emulsion stability are reviewed.
The second part of this paper presents ways to tackle crude oil emulsions. The focus is on the destabilization of emulsions and the demulsification process. Emulsions are destabilized by increasing temperature and residence time, removal of solids, and controlling emulsifiers. The mechanisms involved in demulsification (flocculation, aggregation, sedimentation, creaming, and coalescence) are discussed in terms of the stability of the interfacial films. The methods involved in demulsification including thermal, mechanical, electrical, and chemical are also presented. Experience and economics determine which methods and to what degree each method is used for emulsion treatment.
Finally, a section on field applications is included that should be useful for the practicing engineer who deals with emulsions, either regularly or on a limited basis. Herein the field emulsion treatment program is discussed, and more importantly, methods to prevent emulsion problems are highlighted. Recommendations are made for reducing and optimizing demulsifier dosage and controlling emulsion problems.
Introduction
Crude oil is seldom produced alone. It is generally commingled with water which creates a number of problems during oil production. Produced water occurs in two ways: some of the water may be produced as free water, i.e. water that will settle out fairly rapidly, and some of the water may be produced in the form of emulsions. Emulsions are difficult to treat and cause a number of operational problems such as tripping of separation equipment in gas-oil separating plants, production of off-spec crude oil, and creating high pressure drops in flow lines. Emulsions have to be treated to remove the dispersed water and associated inorganic salts in order to meet crude specification for transportation, storage and export and to reduce corrosion and catalyst poisoning in downstream processing facilities.
Emulsions can be encountered in almost all phases of oil production and processing: inside the reservoirs, well bores and well heads, wet crude handling facilities, transportation through pipelines, crude storage and during petroleum processing. This paper provides a review of crude oil emulsions. However, the review is limited to the produced oilfield emulsions at the well head and at the wet crude handling facilities. It looks at the characteristics, occurrence, formation, stability, handling and breaking of produced oilfield emulsions.
A crude oil emulsion is a dispersion of water droplets in oil. Produced oil-field emulsions can be classified into three broad groups:Water-in-oil (W/O)Oil-in-water (O/W)Multiple or complex emulsions