In the terrestrial environment, interactions between natural organic matter (NOM) and colloids can lead to the formation of an environmental corona around colloids, influencing their transport behaviour and, ultimately, their ecotoxicity. We used a synthetically designed colloid tagged with DNA (DNAcol) as a surrogate for natural colloids and investigated its transport in saturated sand columns. We varied the concentrations of NOM and ionic strength (CaCl₂), to better understand the transport and release of DNAcol in porous media under both steady and transient porewater chemistry conditions. In addition, we aimed to understand the main factors that control deposition and release of DNAcol under tested conditions. To induce transient chemistry, we replaced the injection solution containing NOM and/or CaCl₂ with Milli-Q water. The results showed that the deposition rate of DNAcol was inversely proportional to the concentration of NOM. The deposition rate increased significantly even under low ionic strength (CaCl₂) conditions of tested conditions. Notably, the influence of NOM on the transport of DNAcol was most pronounced at the lowest range of [Ca²⁺]/DOC ratios, and the attachment of DNAcol to the sand grains was negligible. Moreover, the results showed while the DLVO theory captured the general trend of experimental results, it significantly underestimated the deposition of DNAcol in the presence of CaCl₂. Under transient porewater chemistry conditions, colloid remobilization was observed upon flushing the column with Milli-Q water, leading to a secondary peak in the breakthrough curves. We observed that under transient porewater chemistry conditions, when the ionic strength of the solution was 10 mM, the magnitude of the remobilization peak was more significant compared to conditions with 1 mM ionic strength. Our work emphasized the complex interplay between water quality on the one hand and deposition and release of colloidal matter in saturated porous media on the other hand.

Low salinity water flooding is a common technique for enhancing oil recovery; however, the mechanism behind the low-salinity effect, positive or negative, is still not fully understood. In the proposed mechanisms, osmosis and emulsification are considered as two potential reasons for explaining the oil remobilization, but the specific contributions on the remobilization are not well studied at pore-scale. In this article, we performed a series of microfluidic experiments to investigate the movement of constrained oil between invading low-salinity brine and residual high-salinity brine. We find that various salinity contrasts over oil films cause different water fluxes through the oil and swelling areas of the trapped brine, resulting in the relocation of oil phases within the pore spaces. A higher salinity contrast (1.7-170 g/L salt concentrations) provides a faster water penetration in oil phases. In the presence of an oil-soluble surfactant, spontaneous emulsification occurs at the interface of low-salinity brine/oil, which enhances almost 100 times the water flux in two oil phases (n-heptane and n-dodecane). We directly observe pore-scale spontaneous emulsification at the low-salinity brine/oil interface but not at the high-salinity brine/oil interface. Furthermore, two scenarios for explaining water transport through the oil phase are proposed: water diffusion due to chemical potential gradient and water transport via reverse micelle or microemulsions movement.

Natural, artificial, and biological porous media can be seen everywhere in our daily lives. Transport phenomena in porous media, such as flow, diffusion, reaction, adsorption and deformation, are encountered in a wide variety of practical applications and scientific interests over widely disparate length scales, from molecular, to pore, core, and field scales. However, determination of transport properties in porous media remains a challenging issue. During the 12^th Annual Meeting of the International Society for Porous Media (InterPore), held online from August 31-September 4, 2020, advances on porous media science and engineering in very broad areas were presented. The meeting was attended by more than 750 participants from across the globe, and a significant milestone was achieved in the history of InterPore conferences due to its online interactive platform. Participants could access the pre-recorded talks, leave comments and questions, chat with each other, one week before the conference. Then, all the feedback related to a talk was discussed in the presence of the author during several Q&A sessions. Invited and Keynote talks were live, and were also recorded. Each Q&A session was moderated by two experts, who first reviewed the 8 contributions of their session and then summarized the questions for each talk. The author could further elaborate their work and answer the questions.