Flow of Dilute Oil-In-Water Emulsions in Porous Media

Date

1999-12

Authors

Mendez, Zuleyka Del Carmen

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Abstract

The flow of dilute oil-in-water emulsions is of critical concern in produced water reinjection. Oil droplets and solids suspended in produced water are often hard to remove and are, therefore, reinjected into subsurface formations. A rapid injectivity decline in such water injection wells is commonly encountered. Eventually, these wells may have to be operated above the fracture gradient. The flow of emulsions in porous media determines the performance and lifetime of such water injection wells. Flow of dilute oil-in-water emulsions in porous media may also be encountered during enhanced oil recovery and stimulation operations. This dissertation is aimed at investigating the mechanisms of permeability impairment caused by the flow of dilute oil-in-water emulsions in cores containing residual oil. The study has both experimental and modeling components. The experimental program consisted of injecting well-characterized oil-in-water emulsions into cores containing a residual oil saturation. The permeability of different sections of the core as well as the droplet concentration and size distribution were measured as a function of time and position. Two crude oils, one from Prudhoe Bay and another from the North Sea (Brent crude oil) were used in core tests. Berea sandstone and Aloxite cores were used as porous media. Experimental results indicated that the presence of residual oil had a profound effect on the measured permeability decline. Droplets were generated from the residual oil present at pore throats after a critical capillary number is exceeded. It was found that high injection rates and low permeabilities enhance droplet formation. The generation of droplets is a primary contributing factor to the permeability reduction observed in different sections in the core. The permeability of the core, the droplet concentrations, the concentration of emulsifier present, the flow rate, and the properties of the crude oil all play important roles in determining the extent and rate of permeability impairment. High pressure gradient, high flow rate, low permeabilities, high oil concentrations and large droplet sizes contribute to a more rapid decline in permeability. It was observed that the permeability decline occurs in two stages, one associated with the injected droplets followed by a second stage during which generation of droplets plays an important role. After the onset of droplet generation, permeability decline is faster and more severe. This stage is evidenced by a high droplet concentration, in excess of the injected droplet concentration.

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