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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 (COâ)-in-water (C/W) foams, nitrogen (Nâ)-in-water (N/W) foams and COâ-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 (orâ~âcylindrical/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 (CâW) 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 hydrophilicâCO<sub>2</sub>-philic balance (HCB) was found
to be in the appropriate range to produce a large reduction in the
CâW 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,
CâW foams were stabilized with apparent foam viscosities up
to 35 cP and foam textures with bubble sizes on the order of 40 ÎŒm
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 CO<sub>2</sub> 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 <sup>1</sup>H NMR technique was identified. The critical
micelle concentration of rafoxanide in the cosolvent is determined
to be 302 ÎŒg/mL using a surface tension method. The solubility
of rafoxanide in 0.1 N NaOH solution is less than 11 ÎŒg/mL.
Interestingly, the apparent solubility increased to 38,400 ÎŒg/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
CO<sub>2</sub>-in-water foams can be stabilized with a viscoelastic
aqueous phase composed of entangled wormlike micelles, even for extremely
high CO<sub>2</sub> volume fractions Ï of 0.95 to 0.98; the
viscosity of these ultradry foams increased by up to 3â4-fold,
reaching more than 100 cP relative to foams formed with conventional
low viscosity aqueous phases. The foam morphology consisted of fine
âŒ20 ÎŒm polyhedral-shaped CO<sub>2</sub> 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 âwaterlessâ
fracturing fluids for recovery of oil and gas in shale, offering the
possibility of a massive reduction in the amount of wastewater