Solid-Liquid-Liquid Wettability of Surfactant-Oil-Water Systems and Its Prediction around the Phase Inversion Point

Wettability of rock minerals and the underlying surface forces: A review of the implications for oil recovery and geological storage of CO2

The wettability of subsurface minerals is a critical factor influencing the pore-scale displacement of fluids in underground reservoirs. As such, it plays a key role in hydrocarbon production and greenhouse gas geo-sequestration. We present a comprehensive and critical review of the current state of knowledge on the intermolecular forces governing wettability of rock minerals most relevant to subsurface fluid storage and recovery. In this review we first provide a detailed summary of the available data, both experimental and theoretical, from the perspective of the fundamental intermolecular and surface forces, specifically considering the roles played by the surface chemistry, fluid properties, as well as other significant factors. We subsequently offer an analysis of the effects of chemical additives such as surfactants and nanoparticles that have emerged as viable means for manipulating wettability. In each example, we highlight the practical implications for hydrocarbon production and CO2 geo-storage as two of the most important current applications. As the physico-chemical mechanisms governing the wetting phenomena are the main focus, special emphasis is placed on nano-scale experimental approaches along with atomic-scale modeling that specifically probe the underlying intermolecular and surface forces. Lastly, we discuss the gaps in the current state of knowledge and outline future research directions to further our fundamental understanding of the interactions and their impact on the wetting characteristics of Earth's minerals.

Fluoropolymer Microemulsion: Preparation and Application in Reservoir Wettability Reversal and Enhancing Oil Recovery

Reservoir wettability is an important factor in the process of reservoir reconstruction. Especially in hydrophilic formation, it is easy to cause a water-locked phenomenon. A new type of fluoropolymer microemulsion was prepared by emulsion polymerization, and its structure and properties were characterized. The average particle size in the prepared emulsion was about 2.0 μm. The emulsion had good stability and wettability reversal performance for the storage of 30 days. After the treatment of 2.0 wt % emulsion, the contact angle between the core and water changed from 26 to 128°, the core surface free energy decreased from 66 to 2.6 mN/m, and the saturated water imbibition amount of the core decreased from 1.38 to 0.15 g. The ability of the fluoropolymer microemulsion to enhance oil recovery was evaluated by the visual displacement experiment. The fluoropolymer microemulsion can increase the displacement efficiency by more than 10%. The wettability of the core changed from hydrophilicity to hydrophobicity, and wettability reversal was achieved.

Design of industrial wastewater demulsifier by HLD-NAC model

The chemical method is one of the treatment techniques for the separation of oil–water emulsion systems. The selection of appropriate demulsifiers for each emulsion system is the most challenging issue. Hydrophilic-lipophilic-deviation (HLD) is a powerful semi-empirical model, providing predictive tools to formulate the emulsion and microemulsion systems. This work aims to apply HLD to obtain an optimal condition for demulsification of oil-in-water emulsion system—real industrial wastewater—with different water in oil ratios (WOR). Therefore, the oil parameter of the contaminant oil and surfactant parameter for three types of commercial surfactants were calculated by performing salinity scans. Furthermore, the net-average-curvature (NAC) framework coupled with HLD was used to predict the phase behavior of the synthetic microemulsion systems, incorporating solubilization properties, the shape of droplets, and quality of optimum formulation. The geometrical sizes of non-spherical droplets (L_d, R_d)—as an indicator of how droplet sizes are changing with HLD—were consistent with the separation results. Correlating L_d/R_d at phase transition points with bottle test results validates the hypothesis that NAC-predicted geometries and demulsification behavior are interconnected. Finally, the effect of sec-butanol was examined on both synthetic and real systems, providing reliable insights in terms of the effect of alcohol for WOR ≠ 1.

Dramatic Slowing Down of Oil/Water/Silica Contact Line Dynamics Driven by Cationic Surfactant Adsorption on the Solid

We report on the contact line dynamics of a triple-phase system silica/oil/water. When oil advances onto silica within a water film squeezed between oil and silica, a rim forms in water and recedes at constant velocity. We evidence a sharp (three orders of magnitude) decrease of the contact line velocity upon the addition of cationic surfactants above a threshold concentration, which is slightly smaller than the critical micellar concentration. We show that, with or without surfactant, and within the range of small capillary numbers investigated, the contact line dynamics can be described by a friction term that does not reduce to pure hydrodynamical effects. In addition, we derive a model that successfully accounts for the selected contact line velocity of the rim. We further demonstrate the strong increase of the friction coefficient with surfactant bulk concentration results from the strongly nonlinear adsorption isotherm of surfactants on silica. From the variations of the friction coefficient and spreading parameter with surface concentration, we suggest a picture in which the part of the adsorbed surfactants that are strongly bound to the silica interface is trapped under the oil droplet and is responsible for the large increase in line friction.

Characterizing the Oil-like and Surfactant-like Behavior of Polar Oils

In this work, a bifunctional model was developed to fit and predict the phase inversion point (PIP) of microemulsions containing polar oils. This model incorporated the hydrophilic-lipophilic difference (HLD) equations, where HLD = 0 at the PIP. The model uses a Langmuir isotherm to account for the interfacial segregation of polar oils as a function of their concentration in the bulk oil phase. The segregated polar oil was treated as being surfactant-like, having a characteristic curvature (Cc). The polar oil in the bulk oil phase was characterized via an equivalent alkane carbon number (EACN). The Cc value was obtained considering deviations in the PIP at low polar oil concentrations. The EACN was determined considering PIP deviations at high polar oil concentrations. Naphthenic acid and dodecanol were used as model polar oils mixed with ionic and nonionic surfactants and nonpolar oils. The EACN of the polar oil was shown to be independent of the EACN of the nonpolar oil and likely independent of the surfactant. The Cc for dodecanol was likely independent of the surfactant used. For naphthenic acid, the Cc was independent of the nonpolar oil, and within a certain surfactant type (ionic, nonionic, or extended ionic), it was likely independent of the surfactant. For the naphthenic acid systems, the segregation predicted via the bifunctional model was consistent with experimental measurements of this segregation. Given that the bifunctional model only involves phase inversion experiments, it is a convenient method to determine the oil-like and surfactant-like nature of polar oils.