(123c) Emulsion Stabilization, Breaking and Inversion: Advantage or Disaster in Flow Assurance

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Emulsion type and stablity are directly linked with the physico-chemical formulation, which is a way to characterize the interaction between the surfactant substances at interface with the oil and water phases.  Crude oil is generally produced with water, and because the natural surfactants, e.g. asphaltenes and resins, are generally quite lipophilic, the mixture result in a water-in-oil (W/O) emulsion. These emulsions have to be broken in the oil production process, or they have to be inverted to the other type, i.e. oil-in-water (O/W) to  transport very viscous crude oils in pipelines. When the conditions are such that gas hydrate can be formed at the interface of water drops, a W/O emulsion could be transformed en an encapsulated drop dispersion. If these solid hydrate covered capsules do not coalesce, no plugging could take place during the transport. This depends on the formulation case which has to stabilize this dispersion. However, such instance is just contrary to the one which is used to break the emulsion at the oil well to separate water. As a consequence, the change in formulation can produce two opposite scenarios. The first one is the separation of water from oil, which is a requirement in the production. The second one is the production of an instability, and even phase inversion, which is going to help coalesce the water, often resulting in a disaster, i.e. the plugging of the pipe by gas hydrate.

Consequently, in the oil production process, the formulation has to be managed in a clever sequence of two opposite steps. In the first one, while the conditions for the formation of gas hydrate are met, the W/O emulsion has to be kept stabilized, even by adding lipophilic surfactants if the natural ones are not sufficient, so that hydrate covered water drops would not coalesce. Then, when the temperature and pressure are appropriate,  in the second step, an hydrophilic surfactant of the demulsifier type should be added to break the emulsion and separate water from oil. Alternatively, an O/W emulsion of low viscosity could be used for pipelining. In practice, the formulation is genertally shifted by a combination of adding surfactants and changing temperature.