Heavy oil is commonly produced in the form of water-in-oil emulsions. It has long been debated whether the emulsions are formed in the reservoir, and if so, what effect they have on the recovery process. This work examines the conditions under which water-in-oil emulsions can form in situ, and their flow properties.

A number of experiments have been carried out in which water and oil were injected as separate phases into a sandpack, and the produced oil analyzed for emulsified water content. We find that emulsified water content is small at low injection rates, but that above some threshold rate, the water content rises rapidly. Dependence of the threshold rate on oil type, oil viscosity, water;oil ratio, pack permeability and pack wettability have all been examined.

Our results suggest that oil phase capillary number, Nc, defined as (oil velocity)x(oil viscosity)/(oil-water IFT) is a natural dimensionless parameter to describe the emulsification threshold. For oil viscosity much greater than that of water, and permeability of the order of a few darcies, threshold Nc is between 104 and 10−3. Such capillary numbers are commonly encountered in near-wellbore flow during heavy oil recovery operations.

Experiments comparing a reservoir oil with mineral oils show similar threshold capillary numbers. The threshold increases with permeability of the medium and is significantly lower in oil-wet compared with water-wet sand. Preliminary results indicate that a significant reduction in effective mobility of the oil phase occurs when emulsification takes place.

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