Propensity of gypsum precipitation using surface energy approach

Impact of various aggregation kinetics on thermophoretic velocity of asphaltene deposition

Asphaltene deposition may pose serious challenges to flow assurance of crude oil in well columns. Different aggregation kinetics would partly be responsible for asphaltene particle growth ending in deposition on the surface of well columns. This work primarily investigates the thermophoretic deposition velocity caused by temperature gradients inside well columns for various asphaltene aggregation kinetics, including crossover behaviour, sedimentation, reaction-limited aggregation (RLA), and diffusion-limited aggregation (DLA). To do so, the experimental observations of size distribution for a live crude oil was performed at 80 °C and pressure range of 4500-5500 psia. Moreover, various patterns of different size distributions were gathered from the literature for the sake of comparison. Next, a well column in southern Iran was selected to study the kinetic behaviour of thermophoretic velocity of deposition, with a difference between geothermal and static temperatures of around 5 to 50 °C. The non-isothermal deposition velocity was shown to decrease from the top to the bottom of the well column, according to the findings of the study. The results also revealed that the thermophoretic velocity decreases as particle size increases and vice versa. This was confirmed by examining a comparably large range of asphaltene particle sizes, ranging from approximately 100 nm to roughly 9 µm. Practical implications of these findings were also discussed which would provide guidance for mitigation of asphaltene deposition in well columns.

Surface Energy and Wetting Behavior of Dolomite in the Presence of Carboxylic Acid-Based Deep Eutectic Solvents

This study endeavors to apply experimental and theoretical analyses to assess the viability of wettability alteration for two carboxylic acid-based deep eutectic solvents (DESs). To prepare these chemicals, oxalic acid and citric acid were used as hydrogen bond donors mixed with choline chloride as the hydrogen bond acceptor in an equimolar ratio. In the theoretical part, dolomite and crude oil were characterized using a three-phase setup. Then, the adhesion propensity of brines/crude oil toward dolomite was evaluated by calculating the work of adhesion. Contact angle and interfacial tension measurements were conducted in the experimental part to investigate the impact of chemicals on brine-crude oil and brine-rock interactions. Results revealed that the oxalic acid-based DES outperformed the citric acid-based DES in terms of interfacial tension reduction. In addition, choline chloride/oxalic acid (1:1) could effectively restore the wettability of the dolomite sample to its original state with a wettability alteration index of 82%. Theoretical calculations also confirmed the wettability alteration potential of DESs. Finally, a correlation was proposed to predict the contact angle of brine on the dolomite surface in the presence of crude oil using surface-energy components of brine, crude oil, and dolomite.

Gypsum Seeding to Prevent Scaling

Eutectic freeze crystallization (EFC) is a novel separation technique that can be applied to treat brine solutions such as reverse osmosis retentates. These are often a mixture of different inorganic solutes. The treatment of calcium sulphate-rich brines using EFC often results in gypsum crystallization before any other species. This results in gypsum scaling on the cooled surfaces of the crystallizer, which is undesirable as it retards heat transfer rates and hence reduces the yield of other products. The aim of this study was to investigate and understand gypsum crystallization and gypsum scaling in the presence of gypsum seeds. Synthetic brine solutions were used in this research because they allowed an in-depth understanding of the gypsum bulk crystallization process and scaling tendency without the complexity of industrial brines. A cooled, U-shaped stainless-steel tube suspended in the saturated solution was employed as the scaling surface. This was because a tube-shaped surface enabled the introduction of a constant temperature cold surface in the saturated solution and most industrial EFC crystallizers are constructed from stainless steel. Gypsum seeding was effective in decreasing the mass of scale formed on the heat transfer surface. The most effective seed loading was 0.25 g/L, which reduced scale growth rate by 43%. Importantly, this seed loading is six times the theoretical critical seed loading. The seeding strategy also increased the gypsum crystallization kinetics in the bulk solution, which resulted in an increase in the mass of gypsum product. These findings are relevant for the operability and control of EFC processes, which suffer from scaling problems. By using an appropriate seeding strategy, two problems can be alleviated. Firstly, scaling on the heat transfer surface is minimised and, secondly, seeding increases the crystallization kinetics in the bulk solution, which is advantageous for product yield and recovery. It was also recommended that the use of silica as a seed material to prevent gypsum scaling should be investigated in future studies.

Impact of Hydrodynamic and Interfacial Interactions on Scale Formation in a Capillary Microchannel

This study proposes a model for the kinetics and hydrodynamics of gypsum scale deposition on surfaces of anhydrite, calcite, dolomite, and sandstone rocks while interacting with the brines of 3000 and 6000 mg/L [Ca²⁺] at 363 K and 1 atm. To do so, this study utilizes the surface energy characteristics of an interacting scale-brine-rock system as well as the geochemical interactions between brine-brine and brine-rock. The results showed that the deposition flux decreases steeply over time, followed by asymptotic propensity as time elapses. A higher degree of salinity in terms of [Ca²⁺] increases the deposition flux as much as 2.9-fold for the flowing velocity of 10^-6 m/s and 2.4-fold for a velocity of 10^-5 m/s. Moreover, higher flow velocity would lead to more deposition on sandstone followed by carbonate and anhydrite rocks: ∼2.6-fold for the salinity of 3000 mg/L and 2.2-fold for 6000 mg/L [Ca²⁺].

New mechanistic insights into the effect of cations on membrane fouling caused by anionic polyacrylamide

HYPOTHESIS

Understanding the effect of cations on membrane fouling is crucial for the widespread application of the membrane technology. However, contradictory results have been reported based on different studies. Moreover, although the effect of the ionic strength has been studied extensively, limited information is available on the effect of the ion type on membrane fouling.

EXPERIMENTS

The physicochemical properties of the membrane and anionic polyacrylamide (APAM) were evaluated to calculate the APAM-membrane and APAM-APAM interfacial interaction energies under different conditions. Moreover, a series of microfiltration (MF) experiments was conducted to investigate the effects of the ionic conditions on the flux decline, pore blockage and cake layer resistances, and the flux recovery rate of APAM during the MF process.

FINDINGS

As the ionic strength increased, the rate of decrease in the normalized flux increased, the total and cake layer resistances increased significantly, the pore blockage resistance was affected slightly, and the recovery rates of the water flux after physical and chemical cleaning decreased gradually, which could be clearly explained using the Derjaguin-Landau-Verwey-Overbeek theory. Furthermore, compared with Na⁺, Ca²⁺ could effectively mitigate the membrane fouling at an identical ionic strength, which is attributed to the hydration forces of APAM-membrane and APAM-APAM.

Universal relation between the density and the viscosity of dispersions of nanoparticles and stabilized emulsions

The effective viscosity of nanoparticle dispersions has been investigated experimentally quite a lot and various behaviours have been observed. Many models have been proposed to predict the effective viscosity, but these are mainly empirical ones, correlations with a tuning parameter or based on fastidious molecular interactions simulations. In this work, we propose a new fully physics-based analytical expression for the effective viscosity implementing theories from extended thermodynamics, including nano-confinement effects, nanoparticle-fluid interactions, density effects, size effects and nanoparticle volume fraction. We validate this model against several different types of nanoparticle dispersions and emulsions and explain the different behaviours using the same model. It appears that the density ratio of the nanoparticles with respect to the fluid plays a crucial role affecting the viscosity. The nanoparticle-fluid interactions become increasingly important for smaller nanoparticle sizes. From these comparisons, we arrive at a general simplified expression for the effective viscosity of nanoparticle dispersions, where it is observed that there is a direct universal relation between the nanoparticles and fluid densities and the nanodispersion viscosities. The validity of such a relation has been explicitly demonstrated.