Chemical Alteration of Wettability of Sandstones with Polysorbate 80. Experimental and Molecular Dynamics Study

In this work experimental and theoretical evaluations of the wettability alteration of sandstones, using the commercial surfactant polysorbate 80 (P80), are presented. The experimental evaluation started from a virgin sandstone core (water-wet); damage was then induced to modify the wettability of the rock from water-wet to oil-wet, with the purpose of evaluating the surfactant’s ability to restore the wettability of the core to the water phase. The contact angles of water and <i>n</i>-decane droplets were used to evaluate the wettability alteration of the surface. The theoretical evaluation was made using molecular dynamics to determine the configuration of the surfactant adsorbed on the surface and to calculate the surfactant–liquid interaction energy. Experimental results showed that a concentration of 100 ppm P80 in the impregnation solution generated the greatest contact angle for <i>n</i>-decane droplets and a small contact angle for water droplets using the least amount of surfactant, restoring the water-wet state of the solid and generating a lipophobic surface. The molecular dynamics results showed that adsorption of the surfactant on the surface is associated mainly with interactions between the chains of the surfactant that contain the ester group and the surface, whereas the chains containing ethylene oxides are exposed toward the liquid phase. By evaluating the interaction energy between the P80 coating and the liquid phases, it was established that the chains containing the ethylene oxides were key to restoring the water-wet state of the surface since they exerted an attractive interaction over water and a slightly repulsive interaction over <i>n</i>-decane, generating the lipophobic surface. The molecular model developed in this work allows the performance of predictive calculations of the contact angle of liquid droplets, with deviations, in most cases, of less than 5% compared to the experimental value

Development of a Population Balance Model to Describe the Influence of Shear and Nanoparticles on the Aggregation and Fragmentation of Asphaltene Aggregates

The precipitation and deposition of asphaltenes is a primary problem related to the processing, transportation, and production of oil. Flocculation of asphaltene aggregates is likely to occur during the production and processing of crude oil. Recently, it has been shown that nanotechnology in the form of nanoparticles is useful for the inhibition or prevention of asphaltene formation damage. Although it is well-known that the adsorption of asphaltenes on the nanoparticle surface would reduce the capacity of these asphaltic compounds to interact with each other, limited studies have been performed regarding the processes and the mechanisms associated with the effect of nanoparticles on the inhibition of the formation damage due to asphaltenes. To better understand this phenomenon from a mathematical approach, a population balance model (PBM) is proposed to describe the kinetics of asphaltene flocculation-fragmentation in the presence of nanoparticles. The model assumes that asphaltenes in the presence of a shear rate are related to the aggregation and fragmentation phenomena and includes a term related to the asphaltene adsorption on nanoparticles. An adsorption kinetic term was introduced into the model using the double exponential model. Experimental data of the kinetics of asphaltene aggregation were obtained by dynamic light scattering (DLS) measurements at a fixed initial asphaltene concentration of 1000 mg/L and with different Heptol mixtures. In this study, commercial silica, γ-alumina, and magnetite nanoparticles were used as adsorbents to study the effect of the chemical nature of the nanoparticles on the inhibition of the asphaltene growth and for model validation. Additionally, to demonstrate the versatility of the proposed model, the effect of asphaltene was also evaluated. The obtained results from the proposed population balance model agree well with the experimental data, within an RSME % < 9%

Influence of Asphaltene Aggregation on the Adsorption and Catalytic Behavior of Nanoparticles

This study is a continuation of our previous works on the use of metal-based nanoparticles for the adsorption of asphaltenes and its subsequent catalytic thermal decomposition. In this study, we evaluated the effects of asphaltene aggregation on the adsorption process and the subsequent catalytic oxidation using fumed silica and nanoparticles of NiO and/or PdO supported on fumed silica. Adsorption isotherms were constructed through batch adsorption experiments at 25 °C by using mixtures of <i>n-</i>heptane and toluene in amounts of 0, 20% v/v <i>n-</i>heptane (Heptol 20), and 40% v/v <i>n-</i>heptane (Heptol 40) to obtain different aggregate sizes of asphaltenes. Subsequently, asphaltene oxidation in the presence and absence of the nanoparticles was carried out in a TGA/FTIR system to investigate the impact of adsorbed asphaltene aggregates on the catalytic activity of the selected nanoparticles. The adsorption isotherms were described by the solid–liquid equilibrium (SLE) model, and the catalytic behavior of the nanoparticles was compared based upon the trend of effective activation energies using the isoconversional method of Ozawa, Flynn, and Wall (OFW method). The results showed that the <i>K</i> parameter of the SLE model for both nanoparticles followed the trend of Heptol 40 > Heptol 20 > toluene, indicating that, as the amount of precipitant in the solution increases, a higher degree of asphaltene self-association on the active site of the catalysts is found. On the other hand, the <i>H</i> parameter revealed higher adsorption affinities as the <i>n-</i>heptane in the solution increased. However, when different adsorbents were compared at a fixed asphaltene concentration from the same solution, it was found that the use of functionalized nanoparticles led to a lower degree of asphaltene self-association and a higher affinity. A correlation between the effective activation energies from the OFW model and the SLE parameters was developed, finding that, for a fixed adsorbent, <i>E</i>_α increases as the affinity and the degree of self-association of asphaltenes increases. However, when the same asphaltenes were compared using different adsorbents, it was observed that <i>E</i>_α increases as the affinity decreases and the degree of asphaltene self-association increases. Consequently, this work shows the effect of the adsorption process on the catalytic activity of the nanoparticles. The reported results should give a better context for the use of such nanoparticles for the upgrading of heavy and extra-heavy oil

Role of Particle Size and Surface Acidity of Silica Gel Nanoparticles in Inhibition of Formation Damage by Asphaltene in Oil Reservoirs

The main objective of this study is to evaluate the effect of particle size and surface acidity of synthesized silica gel nanoparticles on the inhibition of formation damage caused by asphaltene precipitation/deposition. Silica gel nanoparticles were synthesized through the sol–gel method, and their characterization was performed via N₂ physisorption at −196 °C, field emission scanning electron microscopy (FESEM), dynamic light scattering (DLS) measurements, and NH₃ temperature-programmed desorption (TPD). The size of the synthesized nanoparticles ranged from 11 to 240 nm. The ability of the nanoparticles to adsorb asphaltenes and to reduce asphaltene self-association was evaluated using batch-mode experiments. The kinetics of asphaltene aggregate growth in the presence and absence of nanoparticles were evaluated using DLS measurements in different Heptol solutions. The smallest nanoparticles (11 nm) had the highest adsorptive capacity for <i>n</i>-C₇ asphaltenes among the nanoparticles studied. Therefore, these nanoparticles were modified using acid, base, and neutral treatments, which showed the following order S11A ≫ S11B ≃ S11N ≃ S11 according to the <i>n</i>-C₇ asphaltene affinity and the reduction of its mean aggregate size in the bulk phase. The surface acidity values obtained through of temperature-programmed desorption test ranged from 1.07 and 1.32 mmol/g. In general, the asphaltene self-association was reduced to a higher degree as the amount of adsorbed asphaltene increased. Additionally, in this study, the performance of a nanofluid treatment was tested under flow conditions in porous media under typical reservoir conditions using the nanoparticles with the best performance in batch-mode experiments. Indeed, nanofluid treatment with silica nanoparticles increased the effective permeability to oil and enhanced the oil recovery with an increase in the recovery factor of 11% under the conditions reported here. This approach has the major benefit of being scalable to a producing field, and the study provides an understanding of the roles of size and surface acidity of silica nanoparticles in the wettability alteration and inhibition of formation damage caused by asphaltenes and their influences on asphaltene aggregate size in the oil matrix and the adsorbed phases