CO2/water foams are of interest for mobility control in CO2 EOR and as energized fracture fluids, or hybrid processes that combine aspects of both processes. In fracturing applications, it would be desirable to lower the water level as much as possible to minimize the production of wastewater and formation damage. It is challenging to stabilize ultra dry foams with extremely high internal phase gas fraction given the high capillary pressure and the rapid drainage rate of the lamellae between the gas bubbles. However, we demonstrate that these ultra dry CO2-in-water foams may be stabilized with surfactants that form viscoelastic wormlike micelles in the aqueous phase. These wormlike micelles are formed by tuning the surfactant packing parameter with electrolytes or a second oppositely-charged surfactant to stabilize ultradry CO2-in-water foams with foam qualities as high as 0.98 and apparent viscosities more than 100 cP up to 90 °C. Applicability of these foams for improved oil recovery is evaluated by running multiphase flow injection simulations in a case-study oil reservoir.
The use of foam in gas enhanced oil recovery (EOR) processes has the potential to improve oil recovery by reducing gas mobility. Nanoparticles are a promising alternative to surfactants in creating foam in the harsh environments found in many oil fields. We conducted several CO2-in-brine foam generation experiments in Boise sandstones with surface-treated silica nanoparticle in high-salinity conditions. All the experiments were conducted at the fixed CO2 volume fraction (g = 0.75) and fixed flow rate which changed in steps. We started at low flow rates, increased to a medium flow rates followed by decreasing and then increasing into high flow rates. The steady-state foam apparent viscosity was measured as a function of injection velocity.
The foam flowing through the cores showed higher foam generation and consequently higher apparent viscosity as the flow rate increased from low to medium and high velocities. At very high velocities, once foam bubbles were finely textured, the foam apparent viscosity was governed by foam shear-thinning rheology rather than foam creation. A noticeable "hysteresis" occurred when the flow velocity was initially increased and then decreased, implying multiple (coarse and strong) foam states at the same superficial velocity.
A normalized generation function was combined with CMG-STARS foam model to cover the full spectrum of foam flow behavior observed during the experiments. The new foam model successfully captures foam generation and hysteresis trends observed in presented experiments in this study and other foam generation experiments at different operational conditions (e.g. fixed pressure drop at fixed foam quality, and fixed pressure drop at fixed water velocity) from the literature.
The results indicate once foam is generated in porous media, it is possible to maintain strong foam at low injection rates. This makes foam more feasible in field applications where foam generation is limited by high injection rates (or high pressure gradient) that may only exist near the injection well. Therefore, understanding of foam generation, and foam hysteresis in porous media and accurate modeling of the process are necessary steps for efficient foam design in field.
The immense nanotechnology advances in other industries provided opportunities to rapidly develop various applications of nanoparticles in the oil and gas industry. In particular, nanoparticle has shown its capability to improve the emulsion stability by generating so-called Pickering emulsion, which is expected to improve EOR processes with better conformance control. Recent studies showed a significant synergy between nanoparticles and very low concentration of surfactant, in generating highly stable emulsions. This study's focus is to exploit the synergy's benefit in employing such emulsions for improved mobility control, especially under high-salinity conditions.
Hydrophilic silica nanoparticles were employed to quantify the synergy of nanoparticle and surfactant in oil-in-brine emulsion formation. The nanoparticle and/or the selected surfactant in aqueous phase and decane were co-injected into a sandpack column to generate oil-in-brine emulsions. Four different surfactants (cationic, nonionic, zwitterionic, and anionic) were examined, and the emulsion stability was analyzed using microscope and rheometer.
Strong and stable emulsions were successfully generated in the combinations of either cationic or nonionic surfactant with nanoparticles, while the nanoparticles and the surfactant by themselves were unable to generate stable emulsions. The synergy was most significant with the cationic surfactant, while the anionic surfactant was least effective, indicating the electrostatic interactions with surfactant and liquid/liquid interface as a decisive factor. With the zwitterionic surfactant, the synergy effect was not as great as the cationic surfactant. The synergy was greater with the nonionic surfactant than the zwitterionic surfactant, implying that the surfactant adsorption at oil-brine interface can be increased by hydrogen bonding between surfactant and nanoparticle when the electrostatic repulsion is no longer effective.
In generating highly stable emulsions for improved control for adverse-mobility waterflooding in harsh-condition reservoirs, we show a procedure to find the optimum choice of surfactant and its concentration to effectively and efficiently generate the nanoparticle-stabilized emulsion exploiting their synergy. The findings in this study propose a way to maximize the beneficial use of nanoparticle-stabilized emulsions for EOR at minimum cost for nanoparticle and surfactant
Although EOR with CO2 is practiced domestically on large scale, the potential for advancement is enormous. The ongoing search for better solutions has motivated extensive research on alternatives to surfactant-stabilized CO2 foams for CO2 mobility control. The formation of CO2-in-water foams lowers the CO2 mobility, resulting in improvement in sweep efficiency in field tests. The crucial unmet challenge in employing CO2 foams is to maintain long-term stability of foam to achieve high sweep efficiency for the duration of the flooding process. Surfactant-stabilized foams are inherently unstable so that maintenance of the low mobility requires continuous regeneration of lamellae in the small pores of the rock. Nanoparticles can potentially be used to provide much higher foam stability and thus long-term mobility control for CO2 floods. They can act like a foaming surfactant without some of the surfactant drawbacks. Here we present a turnkey approach for using surface treated nanoparticles in reservoirs. This involves: tests for stability in brines, transportability through cores, foam generation in beadpacks and cores when co-injected with CO2, quantification of CO2 viscosity enhancement, and finally modeling of field-scale effects. In this paper, we will outline the key details of nanoparticle design for CO2 EOR.
We present biodegradable gold nanoparticles with plasmon resonances in the NIR region that can provide a crucial link between the enormous potential of metal nanoparticles for cancer imaging and therapy and translation into clinical practice.
T. M. Truskett, Johnston, K. P., Maynard, J. A., Borwankar, A. U., Murthy, A. K., Stover, R. J., Wilson, B. K., Dinin, A. K., Laber, J. R., and Gourisankar, S., “Assembling nanoclusters in water for therapy or imaging,” ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, vol. 247. AMER CHEMICAL SOC 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2014.
Upon consideration of dispersant-related research, both before and after the Macondo Well oil release, it can be divided into two general categories: (1) the fundamentals of how dispersants work and the effects that may result from their use (e.g., physicochemical and transport characteristics of drops, bubbles, hydrates, surfactants), and (2) an applied focus that has emphasized the design of new dispersants or an enhancement of the performance of those products that are currently available.
While there is an extensive amount of data relating to dispersants, a main focus has been on the demonstration of their effectiveness in bench tests and examination of the toxicity of dispersants and dispersed oil. As a result, there is a need for an enhanced understanding of dispersant and dispersed oil thermodynamics and their fate and transport, with a goal to translate the science and engineering to the development of new, effective dispersant systems. The focus of the work to be discussed addresses the following areas:
Formation of small oil droplets: Widely dispersed stable oil droplets in the water column are easily accessible to microbes and therefore highly susceptible to degradation. It is important therefore, to understand the fundamental mechanisms of oil breakup and colloidal stabilization in order to develop new and effective dispersants.
Dispersant-related processes under deep sea conditions: Current dispersants have been developed for surface spills. The efficacy of such formulations when applied at the high pressures and low temperatures representative of deep ocean release has not been systematically studied. Because of concomitant gas release at the discharge point, and the pressures involved, the liquid droplet is essentially a gas-expanded liquid which could behave quite differently when treated with dispersant components depending upon how they partition at the phase interfaces, i.e., gas/water, gas/oil, oil/water.
Fluid mechanics of stabilized oil droplets: Droplet transport, as influenced by all thermodynamic variables of relevance under deep sea conditions, is being studied.
Droplet interactions with solid particulates: A better understanding of these processes, either in marine sediments or in the water column, will help predict the environmental fate of the droplets.
Development of alternative dispersants: Based on the knowledge gained with respect to the fundamentals, a key goal is the systematic translation of that understanding to the development of new and improved materials.
This paper summarizes recent work of a collaborative research effort involving investigators from 22 universities, with particular emphasis on increasing the understanding of the science and engineering of oil spill dispersants.
Description of the material. Stable CO2/water (C/W) foams at high temperatures and salinities have been achieved with substituted amines in limestone, sandstone and glass bead packs with permeabilities from 1 to 78 Darcy. Foams were formed upon injection of the CO2 soluble surfactant in the CO2 phase and would be beneficial for improving sweep efficiency in EOR process.Application. Despite significant interest in CO2 foams for EOR, very few studies have reported stable foams at high temperatures (120 °C) and high salinities, which are often encountered in the Middle East and elsewhere. The foams provide mobility control and stabilize the displacement front in CO2flooded zones to improve sweep efficiency.Results, Observations, Conclusions. The amine surfactants are switchable between the nonionic and cationic states with pH or the nature of the solvent. They exhibit nonionic behavior when introduced in the CO2 phase, which favors injectivity, and cationic in the presence of concentrated brine with dissolved CO2. The hydrophilic/lipophilic balance of the amines was tuned by modification of the amine head group or tail length to design strong foams. It was important to increase the basicity of surfactants to enhance the solvation in the aqueous phase over a pH range of 4 to 7. These surfactants were effective in lowering the interfacial tension between water and CO2 at high temperature and salinity. They generated viscous C/W foams in limestone, sandstone and glass bead packs at 120 °C in the presence of 22% TDS brine when surfactants were injected from either the aqueous or CO2 phase. At pH below 6, these surfactants exhibited low oil/water partition coefficients on the order of 0.1 which suggests that these surfactants will have minimal retardation due to partitioning into oil in the EOR process.Significance of Subject Matter. These surfactants stabilized C/W foam at high temperature and salinity, and partitioned to the water phase over dodecane phase for efficient surfactant utilization. The high solubility in CO2 is beneficial for the surfactant to be available along CO2 flow pathways in a reservoir to minimize viscous fingering and gravity override.
Metal oxides have gained significant interest aspseudocapacitor electrodes due to reversible faradaicsurface reactions that allow for high power density andgreater energy storage than carbon based electric doublelayer capacitors. However, classically investigatedmaterials like RuO2, MnO2, and Ni(OH)2 suffer from highcost, low life cycles, or limited potential windows,respectively.1-3 As such, there is growing demand for newmaterials with improved energy storage and stability.Herein, we demonstrate the capacitive characteristics ofthree lanthanum based perovskite type oxides, LaMnO3,LaNiO3, and LaCoO3. Based on the inherent nature ofperovskites to contain oxygen vacancies, we demonstratethrough cyclic voltammetry that perovskites store chargethrough anions in alkaline electrolytes, likely in the formof hydroxides. This hypothesis was tested by inducingextrinsic oxygen vacancies in LaMnO3 through a lowtemperature reduction in H2/Ar. It was found thatsubstoichiometric LaMnO3-δ exhibits ~20% greatercapacitance, highlighting the significance of oxygenvacancies as charge-storage sites in these perovskite typeoxides. Importantly, due to the well-known oxide andproton ionic conduction characteristics of perovskites, wedemonstrate that charge storage is not limited to thesurface of these materials. Rather, it may extend into thebulk of the structure, leading to higher energy storagethan traditional psuedocapacitors which are inherentlylimited by surface confined reactions. As the first study ofthese materials for pseudocapacitor applications, onlymoderate structural and electrochemical optimizationshave been carried out. As such, the high specificcapacitances of >500F/g and high cycling stability for thematerials of this study imply a promising future forperovskite structured pseudocapacitors.
Perovskite catalysts are of great interest as replacements for precious metals and oxides used in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Perovskite electrocatalysts have been shown to have greater specific activities than precious metals and their oxides, but high mass activities have not yet been realized due to vague or incomplete mechanistic understanding of catalysts active sites coupled with inadequate synthesis techniques which often result in unwanted phase impurities and micron-scale materials. Herein, we demonstrated precise control over the synthesis of essentially phase pure perovskite nanocrystals with mass activities exceeding that of IrO2 and possessing comparable or greater bifunctional character than leading precious metals such as Ir and Pt. The robust aqueous synthesis of ABO3 perovskites such as LaCoO3, LaMnO3, LaNixFe1-xO3 and Ba0.5Sr0.5Co0.8Fe0.2O3-δ will be demonstrated, and the resulting electrocatalytic activities of these materials will be presented. We will examine these results in the context of proposed perovskite activity descriptors, surface hydroxylation, oxygen vacancies and mechanistic pathways for the OER and ORR. Catalytic activity is determined using electroanalytical techniques such as rotating disk electrochemistry and cyclic voltammetry in conjunction with materials characterization enabled by dynamic light scattering, electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and X-ray diffraction. It is demonstrated that these highly active perovskite catalysts are an emerging replacement for the precious metals used not just for the OER and ORR, but also for the chlor-alkali and oxygen depolarized cathode industries as well.
Foams used for mobility control in CO2 flooding, and for more secure sequestration of anthropogenic CO2, can be stabilized with nanoparticles, instead of surfactants, bringing some important advantages. The solid nature of the nanoparticles in stabilized foams allows them to withstand the high-temperature reservoir conditions for extended periods of time. They also have more robust stability because of the large adsorption energy required to bring the nanoparticles to the bubble interface.
Silica nanoparticle-stabilized CO2-in-brine foams were generated by the co-injection of CO2 and aqueous nanoparticle dispersion through beadpacks, and through unfractured and fractured sandstone cores. Foam flow in rock matrix and fracture, both through Boise and Berea sandstones, was investigated. The apparent viscosity measured from foam flow in various porous media was also compared with that measured in a capillary tube, installed downstream of beadpacks and cores.
The domain of foam stability and the apparent foam viscosity in beadpacks was first investigated with focus on how the surface wettability of nanoparticles affects the foam generation. A variety of silica nanoparticles without any surface coating and with different coatings were tested, and the concept of hydrophilic/CO2-philic balance (HCB) was found to be very useful in designing surface coatings that provide foams with robust stability. Opaque, white CO2-in-water foams (bubble diameter < 100 µm) were generated with either polyethyleneglycol-coated silica or methylsilyl-modified silica nanoparticles with CO2 densities between 0.2 and 0.9 g/cc. The synergistic interactions at the surface of nanoparticles (bare colloidal silica) and surfactant (caprylamidopropyl betaine) in generating stable CO2 foams were also investigated.
The common and distinct requirements to generate stable CO2 foams with 5-nm silica nanoparticles, in rock matrices and in fractures, were characterized by running foam generation experiments in Boise and Berea sandstone cores. The threshold shear rates for foam generation in matrix and in fracture, both in Boise and Berea sandstones, were characterized. The ability of nanoparticles to generate foams only above a threshold shear rate is advantageous, because high shear rates are associated with high permeability zones and fractures. Reducing CO2 mobility in these zones with foam diverts CO2 into lower permeability regions that still contain unswept oil.