Effects of ions on the characteristics of monolayer at brine/oil interfaces

The advanced waterflooding technologies through salinity and ionic content adjustment can make favorable impacts on rock wettability and oil recovery. In carbonate reservoirs, SmartWater at low ionic strength showed strong chemical interactions with carbonate minerals and oil components. As a result, several hypotheses are proposed in literature as ionic exchange, rock dissolution, surface charges and others. The applied macroscopic and microscopic technologies have certain limitations in identifying the structures at interfaces especially at monolayers. In this paper, advanced Sum Frequency Generation (SFG) spectroscopy is utilized for the first time to characterize the chemical structures of molecules at the brine/oil interfaces. Different brines recipes and model oil are tested to determine the effects of individual and combined ions on the monolayer structures. Stearic acid is also mixed with hydrocarbons to mimic the acidity condition of fluids in the reservoir. The change in the chemical structure is mo nitored with time at a broad wavenumber range from 1,000 to 3,800 cm-1. Distinct spectral signatures of oil components and water ions are detected at different pH conditions. The SFG data is compared with the previous macroscopic wettability results to predict the components that are highly affected during waterflooding and enhanced oil recovery (EOR) processes. This study brings new insights on understanding the chemical structures at the thin monolayers of flat and curved geometric at different aqueous interfaces. The measured spectra, coupled with a wide range of laser polarization settings, and signal intensity trends are discussed in terms of composition, and structure of organic and inorganic components. For example, the intensity for SmartWater at certain wavenumber is three folds higher when compared to high salinity water. This indicates that the interactions at oil/water interfaces are enhanced at lower ionic strengths. In addition, these findings are also confirmed with similar behaviors at a higher salinity brine as connate formation brine. The novelty of this interfacial study can provide better understanding of the reaction mechanisms altering the ionic strength and salinity of injection water and its impact due to the changes in geometric interfaces. Such understanding is also crucial to optimize the chemistry of injection water and its interaction with oil components and carbonate rock, to ultimately alter wettability toward water-wet

Impact of tailored water chemistry aqueous ions on foam stability enhancement

Abstract Generating strong and stable foam is necessary to achieve in-depth conformance control in the reservoir. Besides other parameters, the chemistry of injection water can significantly impact foam generation and stabilization. The tailored water chemistry was found to have good potential to improve foam stability. The objective of this study is to extensively evaluate the effect of different aqueous ions in the selected tailored water chemistry formulations on foam stabilization. Bulk and dynamic foam experiments were used to evaluate the impact of different tailored water chemistry aqueous ions on foam generation and stabilization. For bulk foam tests, the stability of foams generated using three surfactants and different aqueous ions was analyzed using bottle tests. For dynamic foam experiments, the tests were conducted using a microfluidic device. The results clearly demonstrated that the ionic content of aqueous solutions can significantly affect foam stabilization. The results revealed that the foam stabilization in bulk is different than that in porous media. Depending on the surfactant type, the divalent ions were found to have stronger influence on foam stabilization when compared to monovalent ions. The bulk foam results pointed out that the aqueous solutions containing calcium chloride salt (CaCl2) showed longer foam life with the anionic surfactant and very weak foam with the nonionic surfactant. The solutions with magnesium chloride (MgCl2) and CaCl2 salts displayed higher impact on foam stability in comparison with sodium chloride (NaCl) with the amphoteric alkyl amine surfactant. Less stable foams were generated with aqueous solutions comprising of both magnesium and calcium ions. In the microfluidic model, the solutions containing MgCl2 showed higher resistance to gas flow and subsequently higher mobility reduction factor for the injection gas when compared to those produced using NaCl and CaCl2 salts. This experimental study focusing about the role of different aqueous ions in the injection water on foam could help in better understanding the foam stabilization process. The new knowledge gained can also enable the selection and optimization of the right injection water chemistry and suitable chemicals for foam field applications

Effects of ions on the characteristics of monolayer at brine/oil interfaces

The advanced waterflooding technologies through salinity and ionic content adjustment can make favorable impacts on rock wettability and oil recovery. In carbonate reservoirs, SmartWater at low ionic strength showed strong chemical interactions with carbonate minerals and oil components. As a result, several hypotheses are proposed in literature as ionic exchange, rock dissolution, surface charges and others. The applied macroscopic and microscopic technologies have certain limitations in identifying the structures at interfaces especially at monolayers. In this paper, advanced Sum Frequency Generation (SFG) spectroscopy is utilized for the first time to characterize the chemical structures of molecules at the brine/oil interfaces. Different brines recipes and model oil are tested to determine the effects of individual and combined ions on the monolayer structures. Stearic acid is also mixed with hydrocarbons to mimic the acidity condition of fluids in the reservoir. The change in the chemical structure is mo nitored with time at a broad wavenumber range from 1,000 to 3,800 cm-1. Distinct spectral signatures of oil components and water ions are detected at different pH conditions. The SFG data is compared with the previous macroscopic wettability results to predict the components that are highly affected during waterflooding and enhanced oil recovery (EOR) processes. This study brings new insights on understanding the chemical structures at the thin monolayers of flat and curved geometric at different aqueous interfaces. The measured spectra, coupled with a wide range of laser polarization settings, and signal intensity trends are discussed in terms of composition, and structure of organic and inorganic components. For example, the intensity for SmartWater at certain wavenumber is three folds higher when compared to high salinity water. This indicates that the interactions at oil/water interfaces are enhanced at lower ionic strengths. In addition, these findings are also confirmed with similar behaviors at a higher salinity brine as connate formation brine. The novelty of this interfacial study can provide better understanding of the reaction mechanisms altering the ionic strength and salinity of injection water and its impact due to the changes in geometric interfaces. Such understanding is also crucial to optimize the chemistry of injection water and its interaction with oil components and carbonate rock, to ultimately alter wettability toward water-wet

Substrate Dependent Self-Organization of Mesoporous Cobalt Oxide Nanowires with Remarkable Pseudocapacitance

A scheme of current collector dependent self-organization of mesoporous cobalt oxide nanowires has been used to create unique supercapacitor electrodes, with each nanowire making direct contact with the current collector. The fabricated electrodes offer the desired properties of macroporosity to allow facile electrolyte flow, thereby reducing device resistance and nanoporosity with large surface area to allow faster reaction kinetics. Co₃O₄ nanowires grown on carbon fiber paper collectors self-organize into a brush-like morphology with the nanowires completely surrounding the carbon microfiber cores. In comparison, Co₃O₄ nanowires grown on planar graphitized carbon paper collectors self-organize into a flower-like morphology. In three electrode configuration, brush-like and flower-like morphologies exhibited specific capacitance values of 1525 and 1199 F/g, respectively, at a constant current density of 1 A/g. In two electrode configuration, the brush-like nanowire morphology resulted in a superior supercapacitor performance with high specific capacitances of 911 F/g at 0.25 A/g and 784 F/g at 40 A/g. In comparison, the flower-like morphology exhibited lower specific capacitance values of 620 F/g at 0.25 A/g and 423 F/g at 40 A/g. The Co₃O₄ nanowires with brush-like morphology exhibited high values of specific power (71 kW/kg) and specific energy (81 Wh/kg). Maximum energy and power densities calculated for Co₃O₄ nanowires with flower-like morphology were 55 Wh/kg and 37 kW/kg respectively. Both electrode designs exhibited excellent cycling stability by retaining ∼91–94% of their maximum capacitance after 5000 cycles of continuous charge–discharge

Enhanced Rate Performance of Mesoporous Co₃O₄ Nanosheet Supercapacitor Electrodes by Hydrous RuO₂ Nanoparticle Decoration

Mesoporous cobalt oxide (Co₃O₄) nanosheet electrode arrays are directly grown over flexible carbon paper substrates using an economical and scalable two-step process for supercapacitor applications. The interconnected nanosheet arrays form a three-dimensional network with exceptional supercapacitor performance in standard two electrode configuration. Dramatic improvement in the rate capacity of the Co₃O₄ nanosheets is achieved by electrodeposition of nanocrystalline, hydrous RuO₂ nanoparticles dispersed on the Co₃O₄ nanosheets. An optimum RuO₂ electrodeposition time is found to result in the best supercapacitor performance, where the controlled morphology of the electrode provides a balance between good conductivity and efficient electrolyte access to the RuO₂ nanoparticles. An excellent specific capacitance of 905 F/g at 1 A/g is obtained, and a nearly constant rate performance of 78% is achieved at current density ranging from 1 to 40 A/g. The sample could retain more than 96% of its maximum capacitance even after 5000 continuous charge-discharge cycles at a constant high current density of 10 A/g. Thicker RuO₂ coating, while maintaining good conductivity, results in agglomeration, decreasing electrolyte access to active material and hence the capacitive performance