Abstract

A new family of demulsifiers is introduced that very effectively destabilizes water-in-oil emulsions such as those encountered in produced crude oil, particularly oil produced by steam injection or waterflooding. The demulsifiers are unique in their high solubility in water and can, therefore, be effectively used in acid formulations in which demulsifiers are used to prevent sludge formation downhole.

Experimental results are presented on emulsion stability for crude oil-water systems. Such emulsion stability tests allow us to compare the new demulsifier with existing demulsifier formulations such as nonylphenol formaldehyde resins that are extensively used today. Drop coalescence tests are presented to confirm the results of the emulsion stability tests. Dynamic surface tension measurements are used to measure the surface dilational properties of oil water interfaces containing the new demulsifier. It is clearly shown that low characteristic relaxation times and high dilational elastic moduli correlate well with emulsion stability and can be used as a criteria for selecting demulsifier formulations. The variation of interfacial tension with surfactant concentration is presented to measure interfacial areas of the demulsifier molecules adsorbed at the oil/water interface using the Gibbs equation. This also allows us to compute the CMC of the new formulations.

A wide range of surfactant properties can be obtained by changing the degree of functionalization of the base molecule. When used in combination with other demulsifiers it is extremely effective at breaking water-in-oil emulsions. It's water solubility makes it particularly attractive for use in aqueous formulations that are used for well treatment, such as acidizing formulations.

Introduction

Resolving crude oil emulsions is a costly operational problem in most producing fields. Crude oil free from water is required before it can be placed in pipelines for refinery usage. The costs associated with demulsification can be high. Chemical demulsification is usually the cheapest, most convenient and most effective method of breaking or preventing petroleum emulsions.

Petroleum emulsions are formed when the crude oil and formation brine are mixed together under high shear at locations such as the well-head, chokes and valves. The injection of steam, caustic or in-situ combustion processes, for the recovery of heavy oils, results in the production of very stable viscous water-in-oil (w/o) emulsions. Emulsions produced as a result of enhanced oil recovery (EOR) operations involving the use of surfactants or miceller solutions are also very stable since they may contain surfactants which had been injected into the formation as a recovery agent.

One of the more significant applications of demulsifiers is in breaking acid sludges that can arise in an acidization treatment. These stable emulsions usually contain formation fines and naturally occuring emulsifying agents present in the crude oil. Fines created by the acidizing process are capable of stabilizing emulsions with many types of crude oils and produced water.

For water injection problems the major concern is the removal of oil droplets dispersed in produced water. Here o/w emulsions need to be destabilized by the addition of water soluble demulsifiers or coagulants. Another important application where demulsification plays an important role is the formation of oil sludges in oil spills. A substantial portion of crude oil that is spilled on the sea readily forms o/w emulsions due to the mixing energy provided by the wave action of the sea. The presence of naturally occurring colloidal materials as well as surfactants formed by oxidization of the crude oil results in thick sludges there can be stable indefinitely. These emulsions result in an increase in oil volume by factor of four to ten times.

Water in the crude oil varies from minute amounts to more than 90% v/v for the various types of emulsions discussed above. In the presence of natural emulsifiers that are soluble, dispersible or wettable in either oil or water, stable emulsions are created. The natural emulsifiers are mostly asphaltenes, resins, paraffins and waxes and inorganic colloids such as clay, silica and carbonates. P. 583^

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