Macro- and Microscale Waterflooding Performances of Crudes which form w/o Emulsions upon Mixing with Brines

We study the micro- and macroscale waterflooding performances of unusual crudes which naturally form tight emulsions (stable after 15 months) upon mixing with water and different brines—including the reservoir brine. These crudes are obtained from a large oil field with stock tank oil viscosities in the range 20–100 cP. The waterflooding tests are conducted at constant injection rates in Berea cores and also in a glass-etched micromodel with and without initial water saturation. With the initial water saturation, the emulsions cause final oil recovery to be significantly lower while the breakthrough is surprisingly suppressed. Pressure data suggests that emulsions are formed in situ in the waterflooding tests both with and without the initial water saturation. The injection pressure data show significant fluctuations after about 3 pore volumes of injection. Both the pressure drop and pressure fluctuations are found to be higher at lower injection rates. Furthermore, the pressure drop is higher in tests with the initial water saturation, which may be related to the formation of water-in-oil (w/o) emulsions during the oil injection into water-saturated cores and subsequent aging. We also observe a pronounced initial pressure spike, which cannot be described by the bulk oil rheology as the oil exhibits only a mild shear thinning behavior. The coreflooding results are qualitatively explained from the viewpoint of deep-bed filtration. The pore-scale waterflooding results reveal the formation of both w/o microemulsions and macroemulsions. We observe the accumulation of w/o emulsions at the oil/water interface and in the dead-end pore spaces. Large emulsion droplets are observed to block a significant portion of a pore, which may be re-entrained and mobilized at higher rates. Overall, the formation of w/o emulsions results in significant production challenges because of high pressure drops, especially for the flow initialization.