Thermodynamic Micellization Model Research Articles

Phase Behavior Modeling of Asphaltene Precipitation for Heavy Crudes: A Promising Tool Along with Experimental Data

Thermodynamic modeling is known as a promising tool for phase behavior modeling of asphaltene precipitation under different conditions such as pressure depletion and CO2 injection. In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, while the oil and gas phases are modeled with an equation of state. The PR-EOS was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on an improved solid model has been developed and used for predicting asphaltene precipitation data for one of Iranian heavy crudes, under pressure depletion and CO2 injection conditions. A significant improvement has been observed in predicting the asphaltene precipitation data under gas injection conditions. Especially for the maximum value of asphaltene precipitation and for the trend of the curve after the peak point, good agreement was observed. For gas injection conditions, comparison of the thermodynamic micellization model and the improved solid model showed that the thermodynamic micellization model cannot predict the maximum of precipitation as well as the improved solid model. The non-isothermal improved solid model has been used for predicting asphaltene precipitation data under pressure depletion conditions. The pressure depletion tests were done at different levels of temperature and pressure, and the parameters of a non-isothermal model were tuned using three onset pressures at three different temperatures for the considered crude. The results showed that the model is highly sensitive to the amount of solid molar volume along with the interaction coefficient parameter between the asphaltene component and light hydrocarbon components. Using a non-isothermal improved solid model, the asphaltene phase envelope was developed. It has been revealed that at high temperatures, an increase in the temperature results in a lower amount of asphaltene precipitation and also it causes the convergence of lower and upper boundaries of the asphaltene phase envelope. This work illustrates successful application of a non-isothermal improved solid model for developing the asphaltene phase envelope of heavy crude which can be helpful for monitoring and controlling of asphaltene precipitation through the wellbore and surface facilities during heavy oil production.

An improvement of thermodynamic micellization model for prediction of asphaltene precipitation during gas injection in heavy crude

Thermodynamic micellization model is known as an appropriate approach for prediction of asphaltene precipitation. However, the reliability (i.e. accuracy) of this model for whole range of pressure or injected gas mole percent must be checked. In practice, the accuracy can be improved by using a suitable characterization method. In this research, a computer code for implementing the thermodynamic micellization model has been developed. Having used this program, we make the prediction of asphaltene precipitation by using data reported in the literature as well as the experimental data obtained from high pressure, high temperature asphaltene precipitation experiments under gas injection conditions. An enhancement to the thermodynamic micellization model has been proposed by applying the characterization method taken from the thermodynamic solid model. This new approach introduces a new matching parameter representing the interaction coefficients between the asphaltene component and light hydrocarbon components. Sensitivity analysis has emphasized that the thermodynamic micellization model is highly sensitive to this new matching parameter, the resin interaction energy parameter (Δ U r ), the interfacial tension between the asphaltene micellar core and the crude ( σ 0), and the concentration of asphaltene monomers in the crude which is in equilibrium with the pure solid asphaltene phase ( X a 1 o n s ) . Finally, the predictions obtained from this approach under gas/solvent injection conditions, resulted in a good agreement with experimental data which shows a significant improvement in comparison to the other matches in the available literature.

Prediction of Asphaltene Precipitation During Solvent/CO2 Injection Conditions: A Comparative Study on Thermodynamic Micellization Model With a Different Characterization Approach and Solid Model

Summary There are different thermodynamic models that have been applied for modelling of asphaltene precipitation caused by various reasons, such as solvent/CO2 injection and pressure depletion. In this work, two computer codes based on two different asphaltene precipitation thermodynamic models--the first being the thermodynamic micellization model with a different characterization approach and the second being the solid model--have been developed and used for predicting asphaltene precipitation data reported in the literature as well as in the obtained data for Sarvak reservoir crude, which is one of the most potentially problematic Iranian heavy oil reserves under gas injection conditions. For the thermodynamic micellization model, a new approach was obtained by applying the characterization method taken from the thermodynamic solid model for oil component characterization. This new approach introduced a new matching parameter to the model, representing the interaction coefficients between asphaltene components and light hydrocarbon components, which resulted in a significant improvement in the thermodynamic micellization model predictions of asphaltene precipitation data under gas injection conditions. The model parameters obtained from a sensitivity analysis were applied in both thermodynamic models, and the experimental data of asphaltene precipitation were predicted. The asphaltene precipitation predictions from the solid model showed good agreement with the data taken under gas/solvent injection conditions. Especially for the trend of the titration curve after the peak point, reasonable agreements were observed which could rarely be found in the available literature. It has been observed that although the thermodynamic micellization model with a different characterization approach is more complex than the solid model, it is able to predict the trends of asphaltene precipitation curves for gas titration conditions reasonably well. Also, its predictions matched well with more experimental data points in comparison to the solid model predictions.

Prediction of Asphaltene Precipitation for Kuwaiti Crude Using Thermodynamic Micellization Model

A thermodynamic micellization model is used in this work to describe asphaltene precipitation from Kuwaiti crude oil. The model is based on asphaltene and resin micelle formation and then destruction by addition of an alkane. A coin-like aggregate of asphaltene surrounded by resin molecules constitutes the micellar phase. The rest of the asphaltene and resin are dissolved in the bulk phase. A group contribution method was used to predict the critical properties for the asphaltenes, resin, and oil. The Peng−Robinson EOS was used to predict the onset point and to perform flash calculations. The onset point and the amount of asphaltene precipitated were measured. Hexane, heptane, octane, and decane with varying volumes and temperatures were used. The model also was tested using high-pressure data. In both cases, the model could describe the experimental data reasonably well with a mean square error of 0.57%.

Thermodynamic Micellization Model for Asphaltene Precipitation From Reservoir Crudes at High Pressures and Temperatures

Summary Asphaltene precipitation from reservoir crudes has been modeled using liquid-liquid equilibrium; the precipitated heavy phase is assumed to be in the liquid state and to consist of only asphaltene and resin. The light liquid phase is assumed to consist of the monomers of all the components and the micelles. A thermody-namic micellization model and the Peng-Robinson equation of state (EOS) description of all monomers fully describe the ther-modynamic equilibrium state. From the direct minimization of the Gibbs free energy of the liquid-liquid system, the composition and the amount of each of the phases are calculated. The above model is used to calculate precipitation from three different reservoir crudes. Once vapor-liquid equilibrium parameters are obtained, there is no further adjustment of the parameters of the EOS for precipitation calculations. The predictions from the thermodynamic micellization model are in good agreement with the data. The effect of pressure, temperature, and composition on precipitation is properly predicted by the model.

Thermodynamic micellization model for asphaltene precipitation inhibition

AbstractAromatic solvents and oil‐soluble amphiphiles are recognized as asphaltene precipitation inhibitors in oil production and transportation. In the absence of the model describing the effect of these inhibitors on asphaltene precipitation from crudes, proposed is a thermodynamic micellization model explaining the inhibition mechanism for both aromatic solvents and oil‐soluble amphiphiles. The model shows that aromatic solvents are concentrated in the micellar shell, and the interfacial tension between the asphaltene micellar core and shell is reduced as the micelles becomes stabler. A crude, mixed with a small amount of an oil‐soluble amphiphile, achieves a high micellar stability. The amphiphiles behave like resin species of the crude and coadsorb onto the micellar core with resins. The adsorption enthalpy of an amphiphile onto the micellar core is much higher than that of the resin and, therefore, amphiphiles can be very effective inhibitors. The results suggest that the adsorption enthalpy data can be used to screen the amphiphiles for asphaltene precipitation inhibition. For a given oil‐soluble amphiphile, this model can predict the amount of the amphiphile required to inhibit the precipitation.

New applications of equations of state in molecular models of complex fluid mixtures

Two different types of problems are approached by connecting simplified molecular models with equations of state (EOS). For aqueous–organic solutions of gases chemically reacting with solvent, special techniques to handle electrostatic and nonelectrostatic interaction contributions in the calculation of liquid composition and fugacity coefficients are applied for modeling VLE. A modified hole model and the Soave–Redlich–Kwong (SRK) EOS are utilized to describe solubility of gases in water–alkanolamine–acid gas (CO 2, H 2S) mixtures. A polydisperse version of a thermodynamic micellization model proposed earlier is formulated and applied to describe asphaltene phase drop-out from crude oils.

Thermodynamic Micellization Model for Asphaltene Aggregation and Precipitation in Petroleum Fluids

Summary A thermodynamic framework is proposed to describe the structure of asphaltene micelles and precipitation in crude. The asphaltene micelle is assumed to consist of an asphaltene core surrounded by a solvated shell. The shell contains both resin and all the other species except asphaltenes. The theoretical framework consists of the standard Gibbs free energy of micellar formation and the Gibbs free energies ofthe petroleum liquid and the precipitated phase. The standard Gibbs free energy of the micellar formation is modeled as the sum of various contributions including the association between asphaltene molecules in the core, the deformation of asphaltene and resin molecules in the micelle, and the adsorption of resin molecules onto the micellar core. The Gibbs free energy ofthe petroleum liquid phase includes the contributions from the standard state, mixing, and interactions among the species. The precipitated phase is assumed to be an ideal solid mixture of asphaltenes and resin. The direct minimization of the Gibbs free energy of the liquid/solid system is invoked to calculate the micellar structure and composition in crude and the amount and composition of the precipitated phase. The predicted results reveal that the addition of diluents n-C5 to n-C10 leads to asphaltene precipitation; whereas diluents such as C2 or C3 give rise to precipitation of nearly all resin and asphaltenes from crude. These predictions are in agreement with laboratory measurements. The predicted micellar size increases with dilution ratio. This prediction is also in agreement with measured data.

Thermodynamic micellizatin model of asphaltene precipitation from petroleum fluids

AbstractA thermodynamic micellization model is proposed for the description of asphaltene precipitation from petroleum fluids. It describes the solubilization of asphaltene polar species by resin bipolar molecules in the micelles. A simple form of the standard Gibbs free energy of micellization is used. The petroleum fluid is assumed to be a dilute solution with respect to the monomeric asphaltenes, resins, and micelles. The Peng–Robinson equation of state (PR‐EOS) is applied to describe the fugacity of monomeric asphaltene in the bulk of the petroleum fluid. Intermicellar interactions as well as osmotic pressure effects are neglected. The proposed model shows promising results to describe asphaltene deposition from crude mixtures. It predicts the change in precipitation power of different alkane precipitants and the effect of pressure on asphaltene precipitation. The amount and the onset of predicted asphaltene precipitation are sensitive to the amount of resins in the crude. All these results are in line with laboratory observations and oil‐field data.