Design and synthesis of surfactants and nanoparticles for mechanistic studies of foams, emulsions and wettability alteration

Surfactants or nanoparticles are shown to stabilize carbon dioxide (CO₂)-in-water (C/W) foams, nitrogen (N₂)-in-water (N/W) foams and CO₂-in-oil (C/O) emulsions and to alter the wettability of oil-wet calcite surfaces to water-wet. Chapter 2 focuses on developing an understanding of the aqueous and interfacial properties of single viscoelastic surfactants to stabilize C/W foams for extended time with highly viscous aqueous phases. Surface modified amphiphilic silica nanoparticles are then investigated as alternatives to surfactants to increase the stability of C/W and N/W foams. Here, the first examples of nanoparticles with known surface modification that stabilize foams in high salinity brines at elevated temperature are presented. The fundamental understanding gained from surfactant design for C/W foam studies is used to design stabilizers for C/O emulsions. Here, polymeric surfactants with polydimethylsiloxane backbones and pendant linear alkyl chains are designed to stabilize novel C/O emulsions despite the low interfacial adsorption driving force, given the low interfacial tension. Finally, silica nanoparticles with various modifications (anionic, cationic and nonionic) are used to mechanistically study wettability alteration of oil-wet calcite surface to water-wet, especially in high salinity environments.Chemical Engineerin

Origins of pressure dependent permeability in unconventional hydrocarbon reservoirs

Abstract Unconventional hydrocarbon assets represent a rapidly expanding proportion of North American oil and gas production. Similar to the incipient phase of conventional oil production at the turn of the twentieth century, there are ample opportunities to improve production efficiency. In this work we demonstrate that pressure dependent permeability degradation exhibited by unconventional reservoir materials is due to the mechanical response of a few commonly encountered microstructural constituents. In particular, the mechanical response of unconventional reservoir materials may be conceptualized as the superposed deformation of matrix (or ~ cylindrical/spherical), and compliant (or slit) pores. The former are representative of pores in a granular medium or a cemented sandstone, while the latter represent pores in an aligned clay compact or a microcrack. As a result of this simplicity, we demonstrate that permeability degradation is accounted for through a weighted superposition of conventional permeability models for these pore architectures. This approach permits us to conclude that the most severe pressure dependence is due to imperceptible bedding parallel delamination cracks in the oil bearing argillaceous (clay-rich) mudstones. Finally, we demonstrate that these delaminations tend to populate layers that are enriched with organic carbon. These findings are a basis for improving recovery factors through the development of new completion techniques to exploit, then mitigate pressure dependent permeability in practice

Carbon Dioxide-in-Brine Foams at High Temperatures and Extreme Salinities Stabilized with Silica Nanoparticles

The stabilization of carbon dioxide-in-water (C–W) foams with nanoparticles (NPs) becomes highly challenging as the temperature and salinity increase, particularly for divalent ions, as the nanoparticles often aggregate in the brine phase. For silica nanoparticles with a medium coverage (MC) and high coverage (HC) of organic ligands, the hydrophilic–CO₂-philic balance (HCB) was found to be in the appropriate range to produce a large reduction in the C–W interfacial tension (IFT). Furthermore, the nanoparticles were colloidally stable in concentrated brine (15% total dissolved solids, TDS) up to 80 °C. With these interfacially active nanoparticles, C–W foams were stabilized with apparent foam viscosities up to 35 cP and foam textures with bubble sizes on the order of 40 μm at various gas fractional flows (foam qualities) in beadpack experiments. At the foam quality where the apparent viscosity was a maximum (transition quality) in the beadpack, we also produced CO₂ foams in Boise and Berea cores versus temperature with apparent viscosities up to 26 cP at 70 °C and 15% TDS and hysteresis in the apparent viscosity versus the interstitial velocity. The reductions in the IFT and foam strength at elevated temperature were modestly larger for the HC nanoparticles than for the MC nanoparticles but were low for the low-coverage case. Given that the interfacial adsorption increased with salinity up to 15% TDS, the screening of the charge helped drive the particles from the brine phase to the interface, which was necessary to stabilize the foams

Self-Association of Rafoxanide in Aqueous Media and Its Application in Preparing Amorphous Solid Dispersions

Our primary objective is to characterize the self-association of rafoxanide in alkaline media. The second objective is to illustrate the feasibility of using rafoxanide micellar solution as the feed solution to prepare amorphous solid dispersion via spray drying. Rafoxanide is a poorly water-soluble drug. It is a weak acid, and its poor aqueous solubility is due to its hydrophobicity. The surface-active property of rafoxanide has not been previously reported. It was discovered that the addition of a small percentage of organic solvents is required to elevate the solubility of rafoxanide above the critical micelle concentration to allow for the formation of micelles. Our fluorescence decay study confirms the self-association of rafoxanide in a cosolvent consisting of 70%, v/v, NaOH solution and 30%, v/v, acetone. The position of each functional group in the micellar structures using the ¹H NMR technique was identified. The critical micelle concentration of rafoxanide in the cosolvent is determined to be 302 μg/mL using a surface tension method. The solubility of rafoxanide in 0.1 N NaOH solution is less than 11 μg/mL. Interestingly, the apparent solubility increased to 38,400 μg/mL in the presence of 30% acetone as the result of micelle formation. This unique solubility characteristic makes it feasible to prepare rafoxanide amorphous solid dispersions by spray drying a predominantly aqueous (70% 0.1 N NaOH solution and 30% acetone) based feed solution. Povidone and copovidone were both used as polymeric carriers. Based on solid-state characterization, including differential scanning calorimetry, X-ray powder diffraction, and hot-stage polarized light microscopy, our results indicate that rafoxanide solid dispersions prepared using this novel process are amorphous. Approximately 750-fold increase in the concentration of rafoxanide in aqueous media at pH 6.8 was achieved with the amorphous solid dispersions

Ultradry Carbon Dioxide-in-Water Foams with Viscoelastic Aqueous Phases

For foams with ultra low water contents, the capillary pressure is very large and induces rapid drainage that destabilizes the aqueous lamellae between the gas bubbles. However, we show that high-pressure CO₂-in-water foams can be stabilized with a viscoelastic aqueous phase composed of entangled wormlike micelles, even for extremely high CO₂ volume fractions ϕ of 0.95 to 0.98; the viscosity of these ultradry foams increased by up to 3–4-fold, reaching more than 100 cP relative to foams formed with conventional low viscosity aqueous phases. The foam morphology consisted of fine ∼20 μm polyhedral-shaped CO₂ bubbles that were stable for hours. The wormlike micelles were formed by mixing anionic sodium lauryl ether sulfate (SLES) with salt and a protonated cationic surfactant, as shown by cryogenic transmission electron microscopy (cryo-TEM) and large values of the zero-shear viscosity and the dynamic storage and loss moduli. With the highly viscous continuous aqueous phases, the foam lamella drainage rates were low, as corroborated by confocal microscopy. The preservation of viscous thick lamellae resulted in lower rates of Ostwald ripening relative to conventional foams as shown by high-pressure optical microscopy. The ability to stabilize viscous ultra high internal phase foams is expected to find utility in various practical applications, including nearly “waterless” fracturing fluids for recovery of oil and gas in shale, offering the possibility of a massive reduction in the amount of wastewater