Viscosity behavior of silica suspensions flocculated by associating polymers

Laboratory Investigation of Nanofluid-Assisted Polymer Flooding in Carbonate Reservoirs

In the petroleum industry, the remaining oil is often extracted using conventional chemical enhanced oil recovery (EOR) techniques, such as polymer flooding. Nanoparticles have also greatly aided EOR, with benefits like wettability alteration and improvements in fluid properties that lead to better oil mobility. However, silica nanoparticles combined with polymers like hydrolyzed polyacrylamide (HPAM) improve polymer flooding performance with better mobility control. The oil displacement and the interaction between the rock and polymer solution are both influenced by this hybrid approach. In this study, we investigated the effectiveness of the injection of nanofluid-polymer as an EOR approach. It has been observed that nanoparticles can change rock wettability, increase polymer viscosity, and decrease polymer retention in carbonate rock. The optimum concentrations for hydrolyzed polyacrylamide (2000 ppm) and 0.1 wt% (1000 ppm) silica nanoparticles were determined through rheology experiments and contact angle measurements. The results of the contact angle measurements revealed that 0.1 wt% silica nanofluid alters the contact angle by 45.6°. The nano-silica/polymer solution resulted in a higher viscosity than the pure polymer solution as measured by rheology experiments. A series of flooding experiments were conducted on oil-wet carbonate core samples in tertiary recovery mode. The maximum incremental oil recovery of 26.88% was obtained by injecting silica nanofluid followed by a nanofluid-assisted polymer solution as an EOR technique. The application of this research will provide new opportunities for hybrid EOR techniques in maximizing oil production from depleted high-temperature and high-salinity carbonate reservoirs.

Tuning the Morphology of Protein-Inorganic Calcium-Phosphate Supraparticles via Directed Assembly

Understanding the phenomena that govern complex interfacial and directed assemblies is essential for both control and scale-up of particle syntheses. The present work describes an effort to understand, control, and tune the formation of protein-inorganic calcium-phosphate supraparticles that are produced at an oscillating air-water interface created by end-over-end rotation of the synthesis solution. Supraparticles were synthesized under an array of different conditions that varied reagent concentration, the presence of additives, tube size, and rotational speed. Paired with a fluid mechanics model of the end-over-end rotation and dimensional analysis, the sensitivity of the synthesis to physicochemical and mechanical parameters was determined. Surface tension and bubble formation were found to be important criteria for changing the size distribution of supraparticles. Thresholds for the values of the Froude, Iribarren, and rotational Reynolds numbers were identified for narrowing particle size distribution. These results both guide the specific protein-inorganic supraparticle synthesis described here and inform future manipulation and scale-up of other complex interfacial colloidal assemblies.

Thermothickening in solutions of telechelic associating polymers and cyclodextrins

Telechelic associating polymers (hydrophilic ethoxylated backbone, hydrophobic n-alkyl end-groups) form viscous solutions in water due to associations between the hydrophobes. The addition of alpha-, beta-, or gamma-cyclodextrin (CD) substantially reduces the solution viscosity because the CD molecules envelop and sequester the hydrophobes in their hydrophobic cavities. The present paper explores the variation in polymer-CD solution viscosity with temperature. We find that, in the case of alpha-CD alone, the solutions show "thermothickening", i.e., the viscosity increases from 25 to ca. 60 degrees C whereupon it reaches a peak value and then drops. In contrast, solutions with beta- and gamma-CD show monotonic drops in viscosity upon heating. At a fixed polymer content, the thermothickening is higher for higher alpha-CD concentrations. We have also studied how surfactants and lipids impact the thermothickening. Addition of single-tailed micelle-forming surfactants causes the viscosity to revert to the more typical decreasing trend with temperature. However, addition of double-tailed lipids to a polymer/alpha-CD solution accentuates the thermothickening behavior. The thermothickening is explained by the propensity of alpha-CDs to unbind from the hydrophobes and form inclusion complexes with the polymer backbone as the temperature is raised.

Defect generation surrounding nanoparticles in a cross-linked hydrogel network

A detailed understanding of polymer-nanoparticle interactions is a key element in demystifying the reinforcement mechanism for nanocomposites. To decouple the effects of the polymer-nanoparticle interactions from the particle distribution, we utilized polymerized crystalline colloidal arrays based on a thermosensitive hydrogel, poly(N-isopropylacrylamide) (pNIPAAm). First, the hydrogel network structure in the vicinity of the nanoparticles was investigated by the deswelling behavior of particle-filled hydrogels. The addition of nanoparticles led to an increased rate of deswelling when the particle-filled hydrogel was heated beyond the lower critical solution temperature (32 degrees C). To interpret this observation, we have suggested that the polymer network has a significant increase in defects (e.g., dangling chain ends) in the vicinity of the nanoparticles. The apparent percolation threshold associated with the interaction of the nanoparticles was about 20 times smaller than the theoretical percolation threshold of spherical particles. As a consequence, we have determined the thickness of this defect zone to be about 85 nm. This is much larger than the size of the unperturbed linear pNIPAAm chains, suggesting that the polymers that play a role in the adsorption are not constrained segments of polymers bound between cross-link junctions but relatively free chains. This finding enabled us to emulate the adsorption behavior of pNIPAAm hydrogels on the particles by simply adding linear pNIPAAm chains to the particle suspensions. We then prepared silica and polystyrene suspensions with free pNIPAAm chains at a concentration much lower than the overlap concentration c*. A rheological study was conducted to determine the adsorption thickness of linear polymer chains on both silica and polystyrene nanoparticles. No significant adsorption was observed on silica, whereas the resultant thickness of the polymer was 8 nm on polystyrene.

Structure and rheological properties of model microemulsion networks filled with nanoparticles

Model microemulsion networks of oil droplets stabilized by non-ionic surfactant and telechelic polymer C18 -PEO(10k)- C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering (SANS). A Reverse Monte Carlo (RMC) approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R = 10 nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%. q(A-1).