The present work is a part of a thorough and systematic laboratory study of oil-in-water emulsion flow in porous media that we have undertaken recently to investigate the mechanisms of oil-droplet retention and its consecutive effect on permeability. One of our main objectives was to see how the in-depth propagation of producedwater (PW) residual dilute emulsion could impair the permeability during PW reinjection (PWRI). During this casework, we used granular packs of sharp-edged silicon carbide grains and stable and dilute dodecane-in-water emulsions. The flow experiments were performed under well-controlled conditions, and we studied the effect of most of the relevant parameters, including flow rate, salinity, droplet size, and permeability of the porous medium.A careful monitoring of the salinity and the jamming ratio (JR) allowed us to consider and work separately on the two main mechanisms of droplet capture (i.e., surface capture and straining capture). In a previous paper (Buret et al. 2008), we reported on the effect of salinity and flow rate on emulsion flow through porous media where the pore-size/droplet-size ratio (JR) was very high, ensuring that only droplet capture on pore surface is operative. This paper reports on the effect of salinity and JR on both mechanisms, with the main focus being on the induced permeability impairment.We demonstrated that surface capture could induce significant in-depth permeability losses even at a high JR. The maximum reached permeability loss is very sensitive to salinity and flow rate (shear-thinning effect). This maximum is always lower than a limiting value dictated by the surface-coverage jamming limit of random sequential adsorption (RSA) theory. This limiting value increases while decreasing the JR, according to a simple formula extracted from Poiseuille's law with a mean hydrodynamic thickness of the deposited layer close to the droplet diameter (monolayer deposition). Regarding the straining capture, we determined a critical JR of 7 for this mechanism to occur. Preliminary results using only two JR values and one flow rate are presented. Compared to surface capture, the results show that straining capture induces more severe plugging with a lower rate of propagation. The lower the JR is, the more severe the plugging is and the lower the propagation rate is. However, more investigations are still required, notably using various JRs and flow rates to characterize this important mechanism better.

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. Introduction In the oil industry, emulsion flow and retention have attracted a growing interest since 30 years as they are involved in many oil production operations. Several models (Mc Auliffe, C. D., 1973; Devereux, O. F., 1974; Alvarado, D. A. and al, 1979) have been developed over the years but none of them describes the whole damaging process caused by emulsions (Rey, C. and al., 2000). The most accurate and reliable model is based on the deep-bed filtration (Soo, H. and al, 1986) and accounts for the residual permeability reduction and the shape of the breakthrough curve.

The present work is a part of a thorough and systematic laboratory study of oil-in-water emulsion flow in porous media that we have recently undertaken to investigate the mechanisms of oil droplet retention and its consecutive impact on permeability. One of our main objectives was to see how the in-depth propagation of produced water residual dilute emulsion could impair the permeability during Produced water Reinjection (PWRI). During this casework, we used granular packs of sharp-edged silicon carbide grains and stable and dilute dodecane-in-water emulsions. The flow experiments have been performed under well-controlled conditions and we studied the effect of most of the relevant parameters including flow rate, salinity, droplet size and permeability of the porous medium. A careful monitoring of the salinity and the jamming ratio allowed us to consider and work separately on the two main mechanisms of droplet capture, i.e. surface capture and straining capture. In a previous paper, we reported on the effect of salinity and flow rate on emulsion flow through porous media where the pore size to droplet size ratio (jamming ratio) was very high, ensuring so, that only droplet capture on pore surface is operative. This paper reports on the impact of salinity and jamming ratio on both mechanisms with the main focus on the induced permeability impairment. We demonstrated that surface capture could induce significant in-depth permeability losses even at high jamming ratio. The maximum permeability loss reached is very sensitive to salinity and flow rate (shear thinning effect). This maximum is always lower than a limiting value dictated by the surface coverage jamming limit of RSA theory. This limiting value increases while decreasing the jamming ratio according to a simple formula extracted from the Poiseuille's law with a mean hydrodynamic thickness of the deposited layer close to the droplet diameter (monolayer deposition). Regarding the straining capture, we determined a critical jamming ratio value of 7 for this mechanism to occur. Preliminary results using only two jamming ratio values and one flow rate are presented. Compared to surface capture, the results show that straining capture induces more severe plugging with a lower rate of propagation. The lower the jamming ratio, the more severe the plugging and the lower the propagation rate. However, more investigations are still required, notably, using various jamming ratios and flow rates to better characterize this important mechanism. Introduction PWRI-induced injectvity decline Due to the large and increasing stream of oilfield produced waters and to the tightening of environmental regulations, water handling is becoming a major issue for oil industry. Produced water reinjection (PWRI) for oil production support through pressure maintenance and EOR methods is among the best options to convert waste to value and becomes more and more the main destination of oilfield produced waters (Furtado, C.J.A. et al., 2005; Souza, A.L.S. et al., 2005; Abou-Sayed, A.S. et al., 2007). However, even though PWRI is environmentally correct and economically attractive, its implementation is still facing challenges related to injectivity, geomechanics, corrosion, souring, contingency… Produced waters are complex systems that are reactive and biologically-enriched (schmoo, biomass, EOR additives, oil-coated solids, stable emulsions enhanced by microbiological and EOR surfactants, microbial corrosion products…). Even after advanced surface treatment, fluid to be injected still contains solids and residual dilute oil-in-water emulsions that are hard to remove and have a high potential for plugging (Zhang, N.S. et al., 1993; Al-Abduwani, F.A.H. et al., 2001). How this plugging impacts well injectivity depends on other important parameters such as well completion, injection scheme - matrix or fracture injection - and reservoir characteristics (soft or hard formation).