THE MOST IMPORTANT OBJECTIVE OF ANY OIL PRODUCTION FACILITY IS THE SEPARATION OF WATER AND OTHER FOREIGN MATERIALS FROM THE PRODUCED CRUDE.
The breaking of these “crude oil and water emulsions” constitutes one of the more challenging problems in today’s oil producing industry.
Oil leaving the producing facility has to meet a low water content specification. Too high a level of produced water in the exported oil would severely reduce pumping and other transport capacity. Even a small percentage of emulsified water in crude oil increases the cost of pumping due to the larger volume and the higher viscosity of the oil. In addition, the high salinity of the water would cause corrosion and scaling in downstream operations. It is therefore necessary to remove the water and associated salts from the crude oil.
Production of immiscible oil and water through well head chokes and valves, along with the simultaneous action of shear and pressure reduction, often produce stable water-in-oil mixtures. The relative stability of these mixtures depends upon many factors such as water cut, the nature of salts present, the viscosity of the oil, and in particular the indigenous surfactants present in the oil.
Some of the water does not mix with the oil to give a stable mixture. This “free water” readily separates from the oil. More often, the conditions of production are such that a stable mixture is formed. Such a mixture is called an emulsion and must be specially treated before separation can occur.
An emulsion is a mixture of two immiscible liquids, one of which is dispersed as droplets in the other. The liquid in an emulsion that is broken into droplets is known as the dispersed or internal phase, whereas the liquid surrounding the droplets is called the continuous or external phase. Emulsions formed in oil producing operations are predominantly water-in-oil.
Under proper conditions, emulsions are resolved quickly and effectively by chemicals synthesized to have demulsifying properties. To break an emulsion chemically, the chemical must be carried to the interface of the emulsified water and the surrounding oil. In this action, it is believed that the chemical powers the interfacial tension of the oil and water, allowing the dispersed particles to coalesce into larger drops which then separate from the oil.
The success of treating with White emulsion breakers depends on:
• An adequate quantity of the most effective chemical.
• Sufficient agitation to cause thorough mixing of the chemical with the emulsion.
• Where necessary, the addition of heat to facilitate breaking of the emulsion. “Cold treating” may be possible if ambient temperature is above the paraffin cloud point, or if working with a frozen or icy emulsion, the emulsion is first melted. Cold treating usually requires considerably more demulsifier than treating with heat.There is usually an economically effective ratio of chemical to heat, as well as a practical one.
• Proper handling and separation of the gas before settling.
• Sufficient time to permit settling of the released water.
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