Solutions of extended, flexible cylindrical micelles, often known as wormlike micelles, have great potential as the base for viscoelastic complex fluids in oil recovery, drilling, and lubrication. Here, we study the morphology and nanostructural characteristics of a model wormlike micellar fluid formed from erucyl amidopropyl betaine (EAPB) in water as a function of a diverse range of additives relevant to complex fluid formulation. The wormlike micellar dispersions are extremely oleo-responsive, with even as little as 0.1% hydrocarbon oil causing a significant disruption of the network and a decrease in zero-shear viscosity of around 100-fold. Simple salts have little effect on the local structure of the wormlike micelles but result in the formation of fractal networks at larger length scales, whereas even tiny amounts of small organic species such as phenol can cause unexpected phase transitions. When forming mixtures with other surfactants, a vast array of self-assembled structures are formed, from spheres to ellipsoids, lamellae, and vesicles, offering the ultimate sensitivity in designing formulations with specific nanostructural characteristics.

Summary Scale-inhibitor (SI) squeeze treatments are applied extensively for controlling scale formation during oil and gas production. The current research involves phosphonate/metal precipitate studies in the context of precipitation-squeeze treatments. The main focus here is on the precipitation and solubility behavior of the SI_calcium (Ca)_magnesium (Mg) complexes of HEDP (a diphosphonate), DETPMP (a pentaphosphonate), and OMTHP (a hexaphosphonate); these mixed phosphonate/divalent precipitates are denoted as SI_Can1_Mgn2, where n1 and n2 are the stoichiometric ratios of Ca and Mg to SI, respectively. Precipitation experiments with SI_Can1_Mgn2 species were carried out over a temperature range of 20 to 95°C, while varying the Mg/Ca molar ratio over a wide range from all Ca to all Mg. These precipitates were formed in MgCl2·6H2O/CaCl2·6H2O brine solutions with appropriate molar ratios of metals, then separated from the supernatant by filtration. Subsequently, the solubility of the collected precipitate was found in a solution of the same Mg/Ca molar composition from which it was prepared. In this type of experiment, the solubility of the SI_Can1_Mgn2 precipitate without any respeciation is determined. In addition, another type of solubility experiment was carried out for a precipitate formed in a brine with one fixed Mg/Ca ratio; this was subsequently placed into a solution with different Mg/Ca compositions (from all Ca to all Mg). In these experiments, respeciation of the precipitate may occur. We have been able to establish the solubility (Cs) of the precipitates of three SIs (HEDP, OMTHP, and DETPMP) as a function of both temperature and Mg/Ca molar ratio. It has been shown that the solubility of precipitate is in equilibrium with Mg and Ca concentrations in solution, and any change of these parameters leads to solubility variation. All phosphonate/metal precipitates become less soluble with increasing temperature and much more soluble with an increasing proportion of Mg. We have found that any change in Mg/Ca ratio of brine does lead to a redistribution of Ca, Mg, and SI concentrations in a given precipitate and bulk solution, and, hence, leads to some variation in the precipitate solubility. Additionally, the inhibition efficiency (IE) of precipitated and then redissolved HEDP, OMTHP, and DETPMP SIs was tested and compared with the IE of industrial stock products. We show that, unlike polymeric SI precipitates, the inhibition activity of phosphonate SIs does not depend significantly on the precipitation process, and the IE of precipitated and redissolved SI_Ca and SI_Ca_Mg complexes is very close to that of the industrial stock solutions. These results can be used directly for modeling phosphonate precipitation-squeeze treatments, and the significance of these results for field applications is explained.

Often, scale inhibitors (SIs) applied in oilfields are organic phosphorus compounds, either phosphonates, phosphorus containing polymers, or phosphate esters. The latter group of SIs, phosphate esters, have not been as extensively studied as the others and we focus on these in this paper. The current work is focused on the properties of precipitated calcium - phosphate ester (PE) complexes denoted as PE_Can, with the stoichiometry n. SIs, injected into a wellbore during squeeze treatments, can be retained in the formation rock via two main mechanisms, adsorption and precipitation. Precipitation squeeze treatments are often based on the reaction between a SI and divalent cations where the mixed complexes that form, denoted SI_Mn2+, usually havea much lower solubility than the free SI itself. In this work we show, that the phosphate ester precipitation process is quite different from that of SIs commonly used by industry, i.e.phosphonates and polymers. Unlike phosphonate-divalent complexes, the phosphate ester complexes stoichiometry is not sensitive to solution pH. However, it is found that elevated pH of PE/Ca solutions positively affects the activity of the precipitates which form; the higher the precipitation pH, the higher the inhibition efficiency (IE, to barite) of the resulting precipitate. The higher IE was determined for stock, precipitated and then re-dissolved phosphate ester and its supernatant solution. These IE results show that phosphate ester activity is very sensitive to temperature; the IE of all phosphate ester solutions decreases with increasing temperature. This phenomenon probably occurs due to hydrolysis reactions at the higher temperatures which changes the chemistry of the phosphate ester solutions. To check this assumption, Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR) were applied to monitor structural changes occurring in molecules of precipitated and stock phosphate ester solutions. The results obtained in this work are of practical significance for the effective design of phosphate ester precipitation squeeze treatments, since these products offer (i) a more environmentally acceptable alternative to phosphonates, and (ii) a chemical that is significantly easier to detect within produced brine than many polymers used by the industry, many of which are phosphorus free polymers. However, PE scale inhibitors application environment is at lower temperatures, <80°C, relative to phosphonates which can fuctionup to 150°C, and polymers over 200°C.

The aggregation behavior and flow characteristics of systems based on zwitterionic surfactant, erucyl amidopropyl betaine, silica and alumina nanoparticles in a wide range of surfactant concentrations from molecular to micellar solutions were studied using surface tensiometry, conductometry, dynamic and electrophoretic light scattering, and rheology techniques. The adsorption of zwitterionic surfactant molecules occurs on both positively and negatively charged surfaces via an electrostatic interaction mechanism. As a result, addition of a small amount silica nanoparticles (0.5-0.8 wt%) increases the surfactant solution's viscosity by more than two times.