Phase Behavior Measurements Research Articles

Critical evaluation of empirical gas condensate correlations

Compositionally sensitive retrograde fluids or gas condensates are particularly challenging from the standpoint of phase behavior and fluid property measurement as well as modeling. The problem is even more pronounced when dealing with the two extreme types of fluids, i.e., lean (insignificant amount of retrograde liquid) and rich (significant amount of liquid drop out, few psi below the saturation pressure). Given these complications, many researchers have proposed empirical correlations that make use of either the field data such as gas to condensate ratio (GCR) or laboratory data such as compositions, plus fraction characteristics to obtain PVT properties. In this work, using the reported experimental data of 81 gas condensate fluids in the open literature, we have critically evaluated four such empirical correlations. The evaluation focuses on the relationship between C7+ (heptanes plus) mole% and initial producing GCR; dew point prediction; molecular weight prediction; and maximum retrograde condensate (MRC). The C7+ mole% predicted from GCR showed deviations as high as 45% or the differences between the predicted GCR's from the two evaluated correlations were as high as 5000 scf/STB; dew point predictions were over and under estimated by as much as 2000 psia; overall fluid molecular weight differences were as high as 7 units; and MRC overestimated by as much as 115%. Based on this critical evaluation we demonstrate that such type of simplistic empirical approach lacks the accuracy and reliability of obtaining PVT properties that is crucial in the efficient management of gas condensate reservoirs.

Octadecyl ferulate behavior in 1,2-Dioleoylphosphocholine liposomes

Octadecyl ferulate was prepared using solid acid catalyst, monitored using Supercritical Fluid Chromatography and purified to a 42% yield. Differential scanning calorimetry measurements determined octadecyl ferulate to have melting/solidification phase transitions at 67 and 39°C, respectively. AFM imaging shows that 5-mol% present in a lipid bilayer induced domains to form. Phase behavior measurements confirmed that octadecyl ferulate increased transition temperature of phospholipids. Fluorescence measurements demonstrated that octadecyl ferulate stabilized liposomes against leakage, maintained antioxidant capacity within liposomes, and oriented such that the feruloyl moiety remained in the hydrophilic region of the bilayer. Molecular modeling calculation indicated that antioxidant activity was mostly influenced by interactions within the bilayer.

Near infrared spectroscopy applied for high-pressure phase behavior measurements

This work presents a new technique for phase behavior monitoring at high-pressure conditions. The consolidated synthetic method was modified by insertion of a near infrared probe inside the high-pressure variable-volume view cell. A system composed by carbon dioxide and a distilled petroleum fraction was used to validate the proposed methodology. The experiments were performed in the temperature range of 293–333K, carbon dioxide mass fraction of 0.350–0.900 and pressures up to 20MPa. The phase transitions pressures visually observed were compared with those detected by the spectrophotometer and good correlations were obtained with global mean deviation of 1.4%. Besides, it was possible to identify the type of vapor-liquid phase transitions (bubble or dew points) and the position at diagram (before or after the critical concentration) for the liquid–liquid equilibrium. The proposed methodology is promptly extended to several others systems.

High-Pressure Phase Behavior of Poly(lactic-co-glycolic acid), Dichloromethane, and Carbon Dioxide Ternary Mixture Systems

Phase behavior measurements of the (poly(lactic-co-glycolic acid) + dichloromethane + carbon dioxide) ternary system were taken using a variable-volume view cell at temperatures between 313.15 K and 363.15 K and at pressures up to 340 bar in poly(lactic-co-glycolic acid) weight fraction = 1.0 %, 2.0 %, and 3.0 %, respectively. To explain these systems, the hybrid equation of state (Peng–Robinson equation of state + SAFT equation of state) was applied with the van der Waals one-fluid mixing rule. The binary interaction parameters were obtained from the simplex method.

Ammonia as Alkali for Alkaline/Surfactant/Polymer Floods

Summary Ammonia is logistically preferred over sodium carbonate for alkaline/surfactant/polymer (ASP) enhanced-oil-recovery projects because of its low molar mass and the possibility for it to be delivered as a liquid. On an offshore platform, space and weight savings can be the determining factor in deciding whether an ASP project is feasible. Logistics may also be critical in determining the economic feasibility of projects in remote locations. Ammonia as alkali together with a surfactant blend of alkyl propoxy sulfate/internal olefin sulfonate (APS/IOS) functions as an effective alkali. Surfactant adsorption is low, and oil recovery in corefloods is high. Static adsorption tests show that low surfactant adsorption is attained at pH >9, a condition that ammonia satisfies at low solution concentration. It is expected that ammonia has a performance deficiency relative to sodium carbonate in that it does not precipitate calcium from solution. Calcium accumulation in the ammonia ASP solution will occur, caused by ion exchange from clays. The high oil recovery for ammonia and the calcium accumulation in ASP and surfactant/polymer corefloods with APS/IOS blends show that this surfactant system is effective and calcium-tolerant. Also, phase behavior and interfacial-tension (IFT) measurements suggest that APS/IOS blends remain effective in the presence of calcium. Ethylene oxide/propylene oxide sulfates (such as the used APS) are known commercially available, calcium-tolerant surfactants. However, because of hydrolysis, sulfate-type surfactants are suitable for use only in lower-temperature reservoirs. Very different behavior was noticed for phase-behavior measurements with calcium-intolerant surfactants such as alkyl benzene sulfonates and IOS. In this case, calcium addition results in a very high IFT and complete separation of oil and brine. Presumably, this will result in low oil recovery. A preferred approach for ASP offshore with divalent-ion-intolerant surfactants may be the use of a hybrid alkali system combining the attributes of sodium carbonate and ammonia. The concept is to supply the bulk of the alkalinity for an ASP flood by ammonia with all the inherent logistical advantages. A minor quantity of sodium carbonate is added to the formulation to specifically precipitate calcium ions.

Separation of 1,3-propanediol using supercritical CO2 microemulsion with non-ionic surfactant Ls-54: Experiment and simulation

The phase behavior and micro-structure of the supercritical CO2 (scCO2) microemulsion system with non-ionic dodecyl (poly(ethylene-methylethylene glycol)) ether Ls-54 as surfactant are investigated in this study. A synergistic experimental and simulation study highlights the separation of 1,3-propanediol (1,3-PDO) from dilute aqueous solution in fermentation broth using this scCO2 microemulsion system. Phase behavior measurement and all-atom molecular dynamic simulation are carried out on the Ls-54/CO2/H2O ternary system and Ls-54/CO2/H2O/1,3-PDO quaternary system to study the solubilization property of 1,3-PDO. The results not only indicate the formation of the thermodynamic stable microemulsion system, but also demonstrate that 1,3-PDO can be selectively solubilized from dilute aqueous solution using the scCO2 microemulsion system with Ls-54 as surfactant by easily controlling the operating pressure. Moreover, the simulation results reveal that the microemulsion formation depends on the interaction between the water cluster and head groups of surfactant. Therefore, a new formation mechanism of the scCO2 microemulsion system with non-ionic surfactant is proposed. In addition, the size of microemulsion droplets in Ls-54/CO2/H2O/ethanol(EtOH) and Ls-54/CO2/H2O/1,3-PDO/EtOH system with ethanol as co-solvent are obtained using the method of small-angle X-ray scattering (SAXS) experiment, which also confirms the solubilization of 1,3-PDO in scCO2 microemulsion system. This work might provide reference to the purification of polyols in fermentation broth and help to understand the micro-structure and solubilization property of polar compounds in scCO2 microemulsion system.

Acetaminophen, Methocarbamol, Guaifenesin and Mephenesin in Propylene Glycol: Solubility and Phase Behaviour for Use in Medical Industry

Propylene glycol is generally used as inactive solvent for water-insoluble drugs in liquid form for administration orally and intravenously. The phase behaviour of these binary liquid mixtures is not known very well and this knowledge is desirable in the search for better drug design. In order to know the phase behavior, dielectric relaxation (10 -3 Hz – 2 MHz) and differential scanning calorimetry (DSC) measurements have been performed on binary liquid mixtures of propylene glycol with four drugs namely acetaminophen, methocarbamol, guaifenesin, and mephenesin. The glass transition temperature region is examined critically for a step like change in DSC scan at the heating rate of 10 K/min. The DSC scans are found to be unusually broad in the glass transition region, especially for intermediate concentrations. This together with the dielectric spectroscopic results, which revealed two liquid like processes, each following Vogel-Fulcher-Tammanns temperature dependence at all concentrations, point to microheterogeneity in these mixtures. The two processes are attributed to the separated liquid phases rich in pharmaceutical and propylene glycol respectively.

Experimental measurement and correlation of phase behavior for the CO2+heptafluorobutyl acrylate and CO2+heptafluorobutyl methacrylate systems at high pressure

Experimental data of high pressure phase behavior from 313.2 to 393.2 K and pressures up to about 14.3 MPa were reported for binary mixture of 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) and 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (HFBMA) in supercritical carbon dioxide. The high pressure experiment was performed by static method using variable-volume view cell apparatus. The CO2+HFBA and CO2+HFBMA systems are correlated with the Peng-Robinson equation of state using a van der Waals one-fluid mixing rule. The CO2+HFBA and CO2+HFBMA systems exhibit type-I phase behavior with continuous critical mixture curves.

Accurate Phase Equilibrium Measurements of CO2 Mixtures

A new setup for accurate measurement of phase behavior of CO2-rich mixtures relevant for CCS has been designed, covering a range between - 60 and 150°C in temperature and 0.4 and 20MPa in pressure. In order to design safe and efficient infrastructure for CCS, the exact properties of these mixtures are required, and currently there are large knowledge gaps that need to be closed regarding the phase behavior. This paper reports a description of the experimental setup, how uncertainties will be verified and contained, and the very first test measurements performed using the setup.

Experimental phase behavior study of a five-component model gas condensate

In this work, the bubble points and dew points of a multicomponent mixture of methane, butane, heptane, decane and tetradecane as a model mixture representative of a gas condensate, have been measured experimentally. Ten samples with approximately the same composition were prepared and their bubble-point and/or their dew-point pressures were measured at several temperatures. The phase-behavior measurements were carried out in the temperature range of 240–410K, and at pressures up to 21.6MPa. The temperature and pressure ranges of the critical point for this system was measured and the cricondenbar and cricondentherm of the phase envelope were determined. The Peng–Robinson equation of state (PR EOS) was used for modeling of the phase behavior of this system. The PR EOS was able to successfully determine the bubble- and dew-points of this model gas condensate. Using the PR EOS, the retrograde region and liquid drop out characteristic of this model gas condensate were determined.

Equilibrium Properties of (Carbon Dioxide + n-Decane + n-Octadecane) Systems: Experiments and Thermodynamic Modeling

Solubility of carbon dioxide in n-octadecane and in three binary mixtures of n-octadecane and n-decane (0.25, 0.5, and 0.75 mol fractions of n-decane) has been measured at 323 K and at the pressures (1 to 6) MPa. Prior to phase equilibrium measurements, the density and viscosity of n-octadecane and of prepared binary mixtures were measured. Then, the phase behavior measurements were undertaken with an in-house designed PVT apparatus. The solubility of carbon dioxide in liquid hydrocarbons and its effect on the physical properties were examined. Increase in the pressure caused an increase in the carbon dioxide solubility and consequently, a decline in the viscosity of saturated liquid phase and an increase in the density of gas-expanded liquid were observed. The carbon dioxide solubility was lower in the heavier liquid mixture. The experimental data were well modeled with Soave–Redlich–Kwong and Peng–Robinson equations of state. Both equations of state have almost the same predictions for solubility while ...

Phase behavior measurement for poly(isobornyl acrylate) + cosolvent systems in supercritical solvents at high pressure

We have conducted experiments to obtain cloud-point data of binary and ternary mixtures for poly(isobornyl acrylate) [P(IBnA)] (Mw=100,000)+isobornyl acrylate(IBnA) in supercritical carbon dioxide (CO2), P(IBnA) (Mw=100,000)+dimethyl ether (DME) in CO2, P(IBnA) (Mw=100,000) in propane and butane, and P(IBnA) (Mw=1,000,000) in propane, propylene, butane and 1-butene at high pressure conditions. Phase behaviors for these systems were measured at a temperature range from 323.4K to 474.1K and pressure up to 296.7MPa. The cloud-point curves of P(IBnA) (Mw=100,000)+IBnA and DME in CO2 change from upper critical solution temperature (UCST) behavior to lower critical solution temperature (LCST) behavior as IBnA and DME concentration increases, and liquid–liquid–vapor phase behavior appears for the P(IBnA) (Mw=100,000)+CO2+80.3wt.% IBnA system. Phase behaviors of P(IBnA) and 50wt.% IBnA in CO2 and P(IBnA) in propane and butane show the pressure difference in accordance with Mw=1,000,000 and Mw=100,000 of P(IBnA). Also, the solubility curves for IBnA in supercritical CO2 were measured at a temperature range of (313.2–393.2)K and pressure up to 22.86MPa. The experimental results were modeled with the Peng–Robinson equation of state (PR-EOS) using a mixing rule including two adjustable parameters. The critical property of IBnA is estimated with the Joback–Lyderson method.

Experimental results and thermodynamic investigation of carbon dioxide solubility in heavy liquid hydrocarbons and corresponding phase properties

Solubilities of carbon dioxide in n-octadecane and its binary mixtures with n-decane have been reported at 372.8K over the pressure range 1–6MPa. The binary mixtures of n-octadecane and n-decane were prepared at 0.25, 0.5, and 0.75 mole fractions of n-decane. The density and viscosity of n-octadecane and its binary mixtures were first measured. Then, the phase behaviour measurements were undertaken with a designed PVT apparatus to investigate the solubility, gas-expanded liquid density and viscosity when the liquid hydrocarbon was saturated with carbon dioxide. The solubility data showed that the solubility of carbon dioxide in n-decane, n-octadecane, and their binary mixtures rose with pressure and reduced as the mixture became heavier. The data indicated the dissolution of carbon dioxide in pure species or their binary mixtures caused a decline in the viscosity of saturated liquid phase and led to an increase in density of gas-expanded liquid. The solubility and density measurements were then correlated with Soave–Redlich–Kwong and Peng–Robinson equations of state. The volume translation technique and the adjustment of binary iteration parameters were applied to fit the generated data. The modelling results indicated that the volume translation technique should be applied to all components present in the mixture for the densities to be accurately predicted.

Effect of Live Crude on Alkaline/Surfactant Polymer Formulations: Implications for Final Formulation Design

Summary Phase-behavior experiments have identified several surfactant systems that develop high solubilization ratios and low interfacial tension (IFT) with a specific dead paraffinic crude oil at specific salinities. The purpose of this work is to test these surfactant systems with reconstituted live crude. Emulsion-screening tests were performed in sight cells where an equilibrium amount of solution gas is dissolved in the crude at reservoir pressure (1,100 psi). The results indicate that the surfactant is relatively more soluble in the oil phase under these conditions. Thus, a formulated chemical slug for field conditions should contain either less salinity or a more hydrophilic surfactant system than that used in formulations with dead crude. Phase-behavior measurements estimate this offset to be approximately 0.25% less NaCl for the particular live crude in this study. The relevance of this offset is shown by comparing the results of dead-crude corefloods with a live-crude coreflood. A control experiment pressurizing oil with nitrogen at the same condition, 1,100 psi, did not show enhanced relative surfactant solubility in the oil phase.

High-Pressure Phase Behavior of Heptadecafluoro-1-decene and Nonafluoro-1-hexene in Supercritical Carbon Dioxide

High-pressure phase behavior measurements of (CO2 + heptadecafluoro-1-decene) and (CO2 + nonafluoro-1-hexene) binary mixture systems were carried out using a variable volume view cell. The experimental range of temperature and pressure are from 313.2 K to 343.2 K and up to 15 MPa, respectively. The correlation was performed using the Peng–Robinson equation of state and the van der Waals one-fluid mixing rule. The critical constants, Tc and Pc, were estimated by the several group contribution methods. The acentric factor was estimated by the Lee–Kesler method.

A Novel Framework for In-House High throughput Measurements of Lipid Phase Behaviour

The biomechanical properties of lipid bilayers are known to regulate protein function and activity. These include parameters such as the stored elastic stress, lateral pressure profiles, spontaneous curvature, bending rigidity and charge density. Unfortunately, these parameters have only been characterised for a limited number of lipid systems due to lack of high throughput techniques that can make such measurements. We present a novel high-throughput laboratory based small angle X-ray scattering beamline which is aimed at generating a biologically relevant database of parameters for characterizing lipid behaviour. The system, capable of simultaneously running over 100 samples in 8 different temperature controlled environment at a time is capable of undertaking phase behaviour measurements (between 4oC and 80oC) for lipid assemblies under biologically relevant conditions. The system is fully automated and based around a labview widget interface which brings together camera and sample chamber control. Using this platform and fluctuation mode analysis we have determined the biomechanical properties of binary lipid systems and correlated these with in-vitro membrane-protein function. This provides a quantitative framework between membrane composition and structure and membrane protein activity.

Polymer Mediated Depletion Attraction and Interfacial Colloidal Phase Behavior

We report direct measurements of poly(ethylene oxide) (PEO) mediated depletion attraction between colloids and surfaces using total internal reflection microscopy (TIRM) and in quasi-2D colloidal phase behavior using video microscopy (VM). PEO concentration dependent particle-wall depletion attraction is accurately quantified by a modified Asakura–Oosawa (AO) potential. The modified AO potential employs an equation of state, depletion length, and partition coefficient computed using results from renormalization group (RG) theory. Quasi-2D phase behavior measurements are in excellent agreement with Monte Carlo (MC) simulations using the same modified AO potential. The analytically simple modified AO depletion potential accurately captures depletion attraction for a realistic excluded volume polymer system, which suggests it can be generalized to other material systems.

Phase behaviour measurements for the system (carbon dioxide + biodiesel + ethanol) at high pressures

This work reports phase equilibrium measurements for binary system {CO 2(1) + biodiesel(2)} and ternary system {CO 2(1) + biodiesel(2) + ethanol(3)}. The biodiesel (ethyl esters) used in this work was produced from soybean oil, purified and characterised following the standard specification for subsequent use. Nowadays, great interest in biodiesel production processes at supercritical and/or pressurised solvents is observed, such as, non-catalytic supercritical biodiesel production and enzyme-catalyzed biodiesel production, besides the supercritical CO 2 can be an interesting alternative to glycerol separation in the biodiesel purification step. Towards this, the main goal of this work is to study the phase behaviour at high pressure for the binary and ternary systems involving CO 2, biodiesel and ethanol. Experiments were carried out in a high pressure variable-volume view cell with operating temperatures ranging from (303.15 to 343.15) K and pressures up to 25 MPa. The CO 2 molar fraction ranged from 0.4213 to 0.9855 for the system {CO 2(1) + biodiesel(2)}, 0.4263 to 0.9781 for the system {CO 2(1) + biodiesel(2) + ethanol(3)} with a biodiesel to ethanol molar ratio of (1:3), and 0.4317 to 0.9787 for the system {CO 2(1) + biodiesel(2) + ethanol(3)} with a biodiesel to ethanol molar ratio of (1:8). For the systems investigated, vapour–liquid (VL), liquid–liquid (LL) and vapour–liquid–liquid (VLL) phase transitions were observed. The experimental data sets were successfully modelled using the Peng–Robinson equation of state with the classical van der Waals quadratic mixing rule (PR-vdW2) and Wong–Sandler (PR-WS) mixing rule, which provided a better fitting to experimental data.

Phase behavior measurement for the system CO2 + glycerol + ethanol at high pressures

This work reports phase equilibrium measurements for the ternary system CO2+glycerol+ethanol. Experiments were performed in a high pressure variable-volume view cell at temperatures ranging from 303.15K to 343.15K and pressures up to 26MPa. The CO2 molar fraction varied from 0.1308 to 0.9871, and glycerol to ethanol molar ratios studied were 1:12, 1:20, and 1:30. For the systems investigated, vapor–liquid (VL), liquid–liquid (LL), and vapor–liquid–liquid (VLL) phase transitions were observed. Phase equilibrium data measured for the ternary system aim the better understanding of the phase behavior knowledge of the glycerol in the ethanol+CO2 mixture at high pressure system.

Simulation of the phase behaviour of Athabasca vacuum residue + n-alkane mixtures

Phase behaviour measurement and prediction for ill-defined hydrocarbons such as vacuum residue + light hydrocarbons present significant challenges, from view-cell design and operation, to thermolysis reactions at high temperature to fluid speciation and phase stability analysis during equilibrium calculations. In a prior contribution, simulated phase behaviour results for Athabasca vacuum residue + n-decane mixtures based on the Peng–Robinson equation of state were presented. In that work, Athabasca vacuum residue pseudo components that were identified exogenously and parameters for the model were computed from these pseudo components using the Marrero and Gani group contribution method. Here, this thermodynamic model is extended to include Athabasca vacuum residue + n-alkanes from n-pentane to n-dodecane. Only binary interaction coefficient values between residue pseudo components and n-alkanes were tuned. Densities of co-existing liquid phases present in the three-phase regions are calculated and compared to the experimental data for AVR + n-decane. The simulations are in qualitative and quantitative agreement with measurements over a broad ranges of temperature, pressure, and composition. The results presented in this contribution illustrate the reliability of the proposed thermodynamic modeling approach and its potential use as a universal heavy oil modeling tool for the simulation of paraffinic deasphalting, separation and refining processes for ill-defined hydrocarbon mixtures.