Amount Of Precipitated Wax Research Articles

The effect of resins concentration and polarity on the viscosity and impedance of electrically-treated waxy oils

Applying an electric field to waxy oil may significantly improve its cold flowability. Our previous study has demonstrated that the accumulation of asphaltenes and resins on the surface of wax particles, i.e., interfacial polarization of wax particles, is the essential mechanism of this electrorheological phenomenon. The influence of asphaltenes concentration on the performance of the electrical treatment has been studied. In this paper, the influence of the concentration of resins, the most abundant non-hydrocarbon component in crude oil, on electrically-treated waxy oil's viscosity and impedance was investigated for the first time by using model oils containing resins in the concentration range of 0.05 wt% - 5.00 wt%. It is found that the effect of resins concentration on viscosity and impedance is not monotonous, with both the viscosity reduction and impedance increment induced by the electric field decreased first and then increased with increasing resins concentration at a given amount of precipitated wax. Increasing the polarity of resins would alleviate the viscosity reduction and impedance increment. This work further demonstrates that resins accumulation on the wax particles surface does occur.

New two-phase and three-phase thermodynamic models for predicting wax precipitation in hydrocarbon mixtures

One of the major issues in flow assurance is the precipitation and subsequent deposition of paraffin wax in petroleum production systems. A new two-phase multicomponent thermodynamic model based on a continuous thermodynamic phase equilibria employing a three-parameter gamma distribution function has been developed to predict the wax appearance temperature (WAT), the amount of precipitated wax, and the wax content of crude oils. Also, a generalized three-phase multicomponent thermodynamic model based on the combined polymer and regular solution theories of mixtures as well as on equations of state (EOS) is presented. The model utilizes the solid-liquid-vapour phase equilibrium relations with some constraint functions. Furthermore, hinged on the regression analysis of published experimental data, a new set of molecular-weight-dependent thermodynamic properties’ correlations were developed and used to calculate the solid-liquid-equilibrium-ratios ( K i S-L ) for the individual component. The models were validated with data obtained from experiments conducted on 32 different hydrocarbon fluids from the Niger Delta, North Sea, Gulf of Mexico, East Asia, and Middle East fields. Results show that the gamma distribution parameters (α, β, η) can be used to classify hydrocarbon mixtures into three categories: light oils or condensate, waxy oil or asphaltenic oils, and biodegraded oils. Analysis shows that when compared with experimental data, the two-phase thermodynamic model is reliable with the average absolute deviations (AAD%) of 0.80% for paraffinic and waxy oils, 0.42% for paraffinic and waxy condensates, and 4.33% for paraffinic-asphaltenic and biodegraded oils. For the three-phase model, results show that the AAD% for the paraffinic and waxy oils, paraffinic and waxy condensates, and biodegraded oils are 0.93%, 1.03%, and 4.88% respectively. However, the two models slightly overestimate the WAT for biodegraded crude oils. Nevertheless, the generalized thermodynamic models developed have proved to be effective for predicting the onset conditions for wax precipitation during petroleum production and processing. It will prove a helpful tool for the fast and accurate assessment of wax deposition tendencies of hydrocarbon mixtures. • A new two-phase multicomponent thermodynamic model based on a continuous thermodynamic phase equilibria employing a three-parameter gamma distribution function has been developed to predict the wax appearance temperature (WAT), the amount of precipitated wax, and the wax content of crude oils. • A generalized three-phase multicomponent thermodynamic model based on the combined polymer and regular solution theories of mixtures as well as on equations of state (EOS) is also presented. • A new set of molecular-weight-dependent thermodynamic properties' correlations were developed and used to calculate the solid-liquid-equilibrium-ratios (KiS-L) for the individual component. • The gamma distribution parameters (α, β, η) can be used to classify hydrocarbon mixtures into three categories: light oils or condensate, waxy oil or asphaltenic oils, and biodegraded oils. • The models were reliably and successfully validated with extensive data obtained from experiments conducted on 32 different hydrocarbon fluids from the Niger Delta, North Sea, Gulf of Mexico, East Asia, and Middle East fields.

Influence of Wax Precipitation on the Impedance Spectroscopy of Waxy Oils

Impedance spectroscopy (IS) is a widely used nondestructive and high-throughput experimental technique for the characterization of electrical properties of materials. In the petroleum industry, IS is frequently employed to determine the electrical properties of asphaltenes and resins. The electrical properties of waxy crude oils, which correlate significantly with the flowability, however, have received little to no attention in the existing investigations. In this work, we inspected the influence of wax precipitation on IS of waxy crude oil for the first time. The investigation was carried out in a frequency range of 2 × 10–1 to 2 × 104 Hz and a temperature range of 5–60 °C. It was discovered that the Nyquist diagram representing the electrical response of waxy oil evolves from one semicircle to two semicircles as wax molecules precipitate at temperatures below the wax appearance temperature. IS of waxy crude oil can be reproduced by an equivalent circuit model composed of two serially connected constant phase element-ideal resistance combinations (Rbulk|Qbulk – Rwax|Qwax). It was found that the resistor-like contribution from wax in the equivalent circuit model, Rwax, increases with the amount of precipitated wax, whereas the capacitor-like contribution in the equivalent circuit model, Qwax, decreases with the amount of precipitated wax. Furthermore, the flow property of waxy oil, such as viscosity, can be related to the conductivity according to the fractional Walden rule. The entire viscosity–conductivity relationship can be divided into three regions, and each segment of the relationship can be fitted by the fractional Walden rule.

Solid-liquid equilibrium of n-alkanes using Global-TPT2 equation of state

An equation of state (EOS) in the framework of thermodynamic perturbation theory (TPT) is applied to the systems containing n-alkanes and the wax deposition phenomena. The EOS used is derived by Alavi and Feyzi (J. Chem. Phys. 2013, vol.139, 074104) and is comprised of a perturbed-chain reference term based on second-order thermodynamic perturbation theory (TPT2), followed by a square-well perturbation contribution. Since the EOS is developed without any phase related assumptions, it can describe vapor, liquid and solid phases. For this reason we have called the EOS Global-TPT2. The pure component parameters are adjusted to pure n-alkane compounds performing linear optimization algorithm. Solubility temperature of some heavy n-alkanes in the n-hexane and n-heptane solvents is evaluated. Good agreement with the experimental data is observed with Average Absolute Relative Percent Deviation (%AAD) of lower than 2 by adjusting only one binary interaction parameter. In addition, the wax appearance temperature and the amount of precipitated wax are predicted using the Global-TPT2 EOS for two North Sea oil samples and also samples composed of methane plus ternary waxy systems. In all these calculations the same EOS is used for both liquid and solid phases. Even though some simplifying assumptions are applied, the model is proved to be capable of adequately describing the systems containing solid phase.

Investigation of wax precipitation in crude oil: Experimental and modeling

In this work, a series of experiments were carried to investigation of rheological behavior of crude oil using waxy crude oil sample in the absence/presence of flow improver such as ethylene-vinyl acetate copolymer. The rheological data covered the temperature range of 5–30 °C. The results indicated that the performance of flow improver was dependent on its molecular weight. Addition of small quantities of flow improver, can improve viscosity and pour point of crude oil. Also, an Artificial Neural Network (ANN) model using Multi-Layer Perceptron (MLP) topology has been developed to account wax appearance temperature and the amount of precipitated wax and the model was verified using experimental data given in this work and reported in the literature. In order to compare the performance of the proposed model based on Artificial Neural Network, the wax precipitation experimental data at different temperatures were predicted using solid solution model and multi-solid phase model. The results showed that the developed model based on Artificial Neural Network can predict more accurately the wax precipitation experimental data in comparison to the previous models such as solid solution and multi-solid phase model with AADs less than 0.5%. Furthermore, the number of parameters required for the Artificial Neural Network (ANN) model is less than the studied thermodynamic models.

A New DSC-Based Method to Determine the Wax Porosity of Mixtures Precipitated from Crude Oils

Wax precipitation is one of the most important problems in flow assurance. The correct prediction of the wax appearance temperature (WAT) and the wax precipitation curve (WPC) is essential to anticipate potential solutions for this problem. The determination of both WAT and WPC requires reliable data on the amount of precipitated wax and the trapped crude oil remaining in these mixtures. The estimation of the latter is difficult due to the scarcity of experimental methodologies. In this work, a method based on differential scanning calorimetry (DSC) was developed to determine the trapped crude oil of precipitated mixtures. The WPCs were experimentally determined by fractional precipitation and DSC analysis for a variety of crude oils. The comparison of these curves requires the correction of the former by subtracting the trapped crude oil remaining in the precipitated mixtures. The trapped crude oil was calculated using two methods: one based on proton nuclear magnetic resonance (1H NMR) previously developed and the other based on DSC, developed in this work. This method considers that the gel formed when decreasing the temperature contains not only solids, but also occluded crude oil. The values of trapped crude oil estimated by both methods were used to correct experimental WPC. The comparison between corrected WPC and those obtained by DSC analysis showed the superiority of DSC over 1H NMR to calculate the amount of trapped crude oil.

MULTI-SOLID MODEL MODIFIED TO PREDICT PARAFFIN PRECIPITATION IN PETROLEUM FLUIDS AT HIGH TEMPERATURES AND PRESSURES

Athermodynamic structure has been modified in order to calculate cloud point, fluidity and amount of precipitated wax under a wide range of temperature conditions, composition, and high pressures. The model is based on a combination of ideal solution concepts, fluid characterization, and formation of multiple solid phases using Cubic State Equations. The experimental data utilized for testing the prediction capacity and potentiality of a model exhibit different characteristics: continuous series synthetic systems of heavy alkanes, discontinuous series, and dead or living petroleum fluids with indefinite fractions such as C7+, C10+, C20+, and C30+. The samples were taken from the literature, petroleum fluids from the main Colombian reservoirs, and some samples of Bolivian fluids. Results presented in this paper show the minimum standard deviations between experimental data and data calculated with a model. This allows a progress in decision-making processes for flow assurance in reservoirs, wells, and surface facilities in the petroleum industry.

An improved thermodynamic model for wax precipitation from petroleum fluids

In this work, a solid-solution model has been developed for improving the representation of wax precipitation from petroleum fluids. The model takes into account the Poynting correction in the solid fugacity calculation. A characterization procedure has been developed for the true boiling point (TBP) and plus fractions. The paraffin-naphthene-aromatics (PNA) distribution up to C 80 is estimated according to the properties of the TBP and plus fractions with one adjustable parameter. An optimized value for that parameter has been obtained, which can be treated as a constant for most crude oils and gas condensates or as a tunable parameter. The model has been used to predict wax appearance temperatures (WAT) over a wide range of pressures and wax contents as a function of temperatures or pressures for a great number of systems. The average deviation of the calculated WAT is within 1.5 K for the systems with the experimental PNA distribution data of TBP fractions, and 3.0 K for the systems without the experimental PNA distribution data of TBP fractions. The results of the calculated wax formation locus and amount of precipitated wax as a function of temperatures or pressures by the proposed model are in good agreement with the measured data. Moreover, the proposed model has demonstrated the capability of simulating the retrograde phenomenon of gas condensates, which indicates that the amount of precipitated wax first decreases and then increases with pressure decrease in the vapor–liquid–solid phase region at a specified temperature.

Wax Precipitation in Gas Condensate Mixtures

Summary Wax precipitation for gas condensate fluids was studied in detail with a thermodynamic model. It was found that the precipitated wax phase can exhibit retrograde phenomena similar to that in gas condensates. As a result of pressure decrease (at a constant temperature), the amount of precipitated wax may first increase, then decrease, then increase again. The effect of pressure on wax precipitation from gas condensates was also studied. Pressure often shows an opposite effect in wax precipitation to that in liquids; however, the pressure effect is not universal. The model used in this work accounts for both the Poynting correction term and the solid-state phase transitions. Incorporation of these effects reconfirms the suitability of the multisolid phase for wax-precipitation calculations (both the onset and the amount).

Modification of multisolid phase model for prediction of wax precipitation: a new and effective solution method

Problems related to precipitation and crystallization of waxes (solid paraffins) during production, transportation and processing of crude oil, cause major difficulties in these processes. This paper presents a modified multisolid phase model for predicting phase equilibria for oil mixtures taking into account the possible formation of a wax phase. This modified model is able to predict wax appearance point (WAP) and amount of precipitated wax in various oil samples. The vapor and liquid phases are described using the Peng–Robinson EOS. For the first three oil samples, heavy fraction properties are evaluated by use of the average properties method and for the second three oils PNA analysis is used. On the contrary to the original multisolid phase model which considers only liquid and solid(s) phases, this work considers vapor phase (in addition to liquid and solid(s) phases), and, therefore, because of this modification, prediction of pressure and composition effects on WAP will be possible. In this work, pressure effects on dead oil (stock-tank-oil, at above bubble point pressure, that there is not any gas) samples, have been studied and according to predictions suggested by previous works the WAP of oils raise as pressure increase. A second prediction based on the modified multisolid phase model refers to WAP decreases with increase of light component concentration. The calculation results obtained in this work, agree very well with experimental results and results obtained from other works.