Adsorption of interfacially active components at the water/oil interface plays critical roles in determining the properties and behaviors of emulsion droplets. In this study, the droplet probe atomic force microscopy (AFM) technique was applied, for the first time, to quantitatively study the interaction mechanism between water-in-oil (W/O) emulsion droplets with interfacially adsorbed asphaltenes. The behaviors and stability of W/O emulsion droplets were demonstrated to be significantly influenced by the asphaltene concentration of organic solution where the emulsions were aged, aging time, force load, contact time, and solvent type. Bare water droplets could readily coalesce with each other in oil (i.e., toluene), while interfacially adsorbed asphaltenes could sterically inhibit droplet coalescence and induce interfacial adhesion during separation of the water droplets. For low asphaltene concentration cases, the adhesion increased with increasing asphaltene concentration (≤100 mg/L), but it significantly decreased at relatively high asphaltene concentration (e.g., 500 mg/L). Experiments in Heptol (i.e., mixture of toluene and heptane) showed that the addition of a poor solvent for asphaltenes (e.g., heptane) could enhance the interfacial adhesion between emulsion droplets at relatively low asphaltene concentration but could weaken the adhesion at relatively high asphaltene concentration. This work has quantified the interactions between W/O emulsion droplets with interfacially adsorbed asphaltenes, and the results provide useful implications into the stabilization mechanisms of W/O emulsions in oil production. The methodology in this work can be readily extended to other W/O emulsion systems with interfacially active components.

Emulsions with interface-active components at the oil/water interface have long been of fundamental and practical interest in many fields. In this work, the interaction forces between two oil droplets in water in the absence/presence of asphaltenes were directly measured using droplet probe atomic force microscopy (AFM) and analyzed using a theoretical model based on Reynolds lubrication theory and the augmented Young-Laplace equation by including the effects of disjoining pressure. It was revealed that the interaction forces measured between two pristine oil droplets (i.e., toluene) could be well described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, while an additional steric interaction should be included in the presence of asphaltenes in the oil. The surface interaction and the stability of oil droplets in aqueous solution were demonstrated to be significantly influenced by the asphaltenes concentration in oil, salt concentration, pH, and presence of divalent ions (Ca(2+)) in water. Adsorbed asphaltenes at the oil/water interface led to more negative surface potential of the oil/water interface and also induced steric repulsion between oil droplets, inhibiting the drop coalescence and stabilizing the oil-in-water emulsion. Lower pH of aqueous solution could lead to less negative surface potential and weaken the repulsion between oil droplets. Addition of divalent ions (Ca(2+)) was found to disrupt the protecting effects of adsorbed asphaltenes at oil/water interface and induce coalescence of oil droplets. Our results provide a useful methodology for quantifying the interaction forces and investigating the properties of asphaltenes at the oil/water interfaces and provide insights into the stabilization mechanism of oil-in-water emulsions due to asphaltenes in oil production and water treatment.

A primary environmental risk from unconventional oil and gas development or carbon sequestration is subsurface fluid leakage in the near wellbore environment. A potential solution to remediate leakage pathways is to promote microbially induced calcium carbonate precipitation (MICP) to plug fractures and reduce permeability in porous materials. The advantage of microbially induced calcium carbonate precipitation (MICP) over cement-based sealants is that the solutions used to promote MICP are aqueous. MICP solutions have low viscosities compared to cement, facilitating fluid transport into the formation. In this study, MICP was promoted in a fractured sandstone layer within the Fayette Sandstone Formation 340.8 m below ground surface using conventional oil field subsurface fluid delivery technologies (packer and bailer). After 24 urea/calcium solution and 6 microbial (Sporosarcina pasteurii) suspension injections, the injectivity was decreased (flow rate decreased from 1.9 to 0.47 L/min) and a reduction in the in-well pressure falloff (>30% before and 7% after treatment) was observed. In addition, during refracturing an increase in the fracture extension pressure was measured as compared to before MICP treatment. This study suggests MICP is a promising tool for sealing subsurface fractures in the near wellbore environment.

This paper reconsiders evidence from experimental common pool resource games from the perspective of a model of payoff sampling. Despite being parameter-free, the model is able to replicate some striking features of the data, including single-peaked frequency distributions, the persistent use of strictly dominated actionsand stable heterogeneity in choices. These properties can also be accurately replicated using logit quantal response equilibrium (QRE), but only by tuning the free parameter separately for separate games. When the QRE parameter is constrained to be the same across games, sampling equilibrium provides a superior fit to the data. We argue that these findings are likely to generalize to other complex games with multiple players and strategies.