Emulsion Deposition in Porous Media: Impact on Well Injectivity
Authors: Buret S. , Nabzar L. , Jada A. 
Published: June 2014

Emulsions flow is encountered in various pratical applications such as enhanced oil recovery (EOR) processes. The occurence of emulsions can have a detrimental impact on well productivity/injectivity and hence, on the enconomic of many EOR operations. However there is still a lack of clear understanding of how they really behave inside a porous medium.

The present work aims at given new insights into emulsion deposition mechanisms. Different experimental conditions are explored to study the deposition of "stable" oil-in-water (O/W) emulsions inside a porous material.

Porous media made of sharp-edged Silicon Carbide (SiC) grains of 80 μm in diameter and dilute and stable dodecane emulsions in brines were used. The ratio of pore to particle size (jamming ratio) is set high enough to ensure in-depth propagation and hence, an in-depth deposition on pore surface without any other retention mechanism such as straining and plugging. In this study, the effects of salinity and flow rate on droplet deposition are highlighted.

At low salinities, the deposition and the induced permeability reduction are negligible. As SiC is negatively charged, this indicates that oil droplets bear a negative surface charge, even if they are stabilized by a non-ionic surfactant. Increasing the salinity induces a better deposition efficiency and a concomittant increase in permeability reduction by screening surface charges. Moreover, the piston-like displacement of the emulsion front entails that the available surface of each section is almost entirely saturated before the next one is reached. Thereby, the deposition is almost uniform along the core. The breakthrough curves exhibit a delay that increases while increasing the salinity and a plateau value near saturation (C/C0=1). This reveals two different deposition steps characterized by two depositon kinetics which will be described according to well known scaling power law for colloidal spheres.

At high salinity and at the lowest flow rates (in the convection-regime), the maximum permeability reduction reached is in excellent agreement with the predicted value from Random Sequential Adsorption (RSA) model. That was initially developed for hard spheres. That confirms that, for "stable" O/W emulsions, droplets deposit as a single layer probably because of steric hindrance. Interestingly, the permeability reduction reaches its maximum at breakthrough where the surface coverage is close to 54%, as predicted from the RSA theory. However, although the permeability impairment is in agreement with the RSA theory, the total deposited amount of oil is higher than expected from the RSA model predictions. After the breakthrough, the droplet deposition continues increasing but at a very small rate during the aforementioned second deposition step, and this, with no significant impact on permeability. It infers that the deposit may get denser on grain surface owing to droplets distortion. The final surface coverage is thus higher than the upper limit depicted in the RSA theory. Finally, from the desorption and the mean hydrodynamic thickness of the deposition layer, we get some experimental clues that, the droplets are likely to deposit individually and not to coalesce to form a film.