Multiphase flow processes taking place during Enhanced Oil recovery (EOR), CO2 or gas storage, geothermal energy production and utilization, membrane filtration processes etc. are usually accompanied by undesirable phenomena of scaling due to the nucleation and growth mechanisms of sparingly soluble salts in pores or on rock surfaces or other used porous material involved. There are cases in which controlled precipitation of sparingly soluble salts is desired, as in waterproofing of underground structures (e.g. tunnels), prevention of soil erosion using consolidation, stabilization of unconsolidated rocks to avoid or to minimize sand transportation during oil extraction, in biomaterials etc.
During past decades, sparingly soluble salt precipitation mechanisms have been investigated in relation with several parameters such as pH, temperature, ionic composition, the presence of additives in the supersaturated fluids, the presence of seeds etc. Based on these works, basic knowledge concerning salt precipitation has been obtained. Salt precipitation is mostly heterogeneous i.e. the crystal nuclei are formed on a substrate acting as a catalyst for the process, and they grow further into macroscopic crystallites.
Our recent studies have shown that the presence of foreign substances (organic solvents, water-miscible or water-immiscible) in the aqueous supersaturated solutions, affects dramatically the nucleation process. However, to reduce the complexity of the system, despite the fact that most of the natural and engineered porous media used in the aforementioned applications are of mixed (fractional) wettability, the parameter of surface wettability has been overlooked up to date.
The heterogeneity coming from the change of the contact angle of the supersaturated fluid with the pore surface (chemical affinity) could be a significant contribution to the driving force for crystal nucleation and growth by itself. Adding parameters including the presence of organic water-immiscible fluids, results in the formation of oil-water interfaces. The interfacial tension at this site may contribute to the driving force for nuclei creation and crystal growth. In addition, pore surface wettability affects strongly the distribution of fluids interfaces in a porous medium, the displacement patterns and the residual oil saturation and consequently nuclei creation may be affected.
In the case of organic water-miscible fluids or surfactants, parameters such as contact angle of solution with the hydrophobic or hydrophilic pore surface, viscosity and density or the presence of emulsions in the case of surfactants may be the driving forces for nuclei creation. In this project, such phenomena will be investigated in detail from microscale to bed-scale. More specifically in WetμFluid, innovative microfluidic technology shall be employed. This technology has been on the spot of research focused on multiphase flow due to the possibility to visualize ever smaller volumes, in the last decade. Microfluidics may provide a more detailed and representative view of the basic physico-chemical properties of fluids and the underlying mechanisms in nucleation and growth of sparingly soluble salts on surfaces of varied wettability shall be clarified.