Binary Interaction Coefficients Research Articles

Optimizing phase equilibrium predictions for the liquefaction of supercritical water gasification products: Enhancing energy storage solutions through advanced thermodynamic modeling

Supercritical water gasification products typically consist of a vapor mixture consisting of H2 and CO2 with high pressure. Liquefaction of supercritical water gasification products not only allows the vapor mixture to be reduced in volume for easy transportation, but also allows liquid CO2 to be obtained from it, and also serves as a form of energy storage. Under the existing thermodynamic model, the prediction of the liquefaction dew point under high pressure is easily diverged and the accuracy is not enough. In this paper, we obtain the value of CO2+H2 binary interaction coefficient under high pressure kij=0.146 by the fitting method and, which improves the convergence of the predicted phase equilibrium data at high pressure and obtains the results with higher accuracy. In the prediction of dew point of supercritical water gasification products, the fluctuation of H2 content has little effect on the liquefaction pressure, and more significant is the effect of the liquefaction temperature, and it is more economical to carry out the liquefaction work within the range of −30 °C to −5 °C. At the same time, in the liquefaction products lower than −10 °C, the liquid CO2 with the mole fraction of more than 0.9 can be obtained.

The SIT model parameters for interactions of carbonate compounds with sodium and potassium ions accounting for association

The current study is devoted to the determination of the SIT coefficients at 298.15 K for interactions, involving CO2(aq), HCO3−, and CO32‐, with mostly Na+ and K+ ions. The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, that has just one parameter for each cation-anion or a dissolved gas – electrolyte interaction. Among the issues that were met for carbonate systems are the side reactions of hydrolysis and disproportionation in the carbonate solutions, that complicate the analysis of data and lead to unusually large difference, up to 9%, in the values of activity coefficients, determined in different authoritative laboratories. For Na2CO3 and K2CO3 solutions, it was necessary to take into account the reaction of formation of the ionic pair M++CO32‐=MCO3−, with the equilibrium constants β1o equal to log10β1o= 0.75 ± 0.08 for M+=Na+ and to log10β1o= 0.67 ± 0.11 for M+=K+. In all, there are values for more than 20 binary SIT interaction coefficients. All results are valid at 298.15 K, 0.1 MPa.

Study on the Phase Behavior Simulation Method of High-Salinity Reservoirs.

The presence of salinity affects the accuracy of existing correlations used in the equation of state. Moreover, the variation of salinity is often ignored in the systematic analysis of the phase diagram, resulting in a large error in the final calculation result. It is obvious that the conventional phase equilibrium calculation is not applicable in a high-salinity reservoir. By introducing the hydrocarbon-brine binary interaction coefficient and α-function, combined with the definition of salinity, and considering the variation of salinity under different pressure and temperature conditions, a more perfect phase equilibrium calculation model was established. The complete phase diagram was drawn, and the calculation results of salinity distribution are obtained. The effect of the mole percentage of water and salt content on the phase behavior was simulated. Finally, the phase distribution simulation is carried out based on the measured data. The phase state and salinity variation law of a high-salinity reservoir are obtained. According to the fluid composition of different periods, the real phase state of the high-salinity reservoir can be monitored in real time. It can provide a theoretical basis for the gas reservoir development and the dynamic evaluation of gas storage injection and production with a hydrocarbon-brine two-phase system.

Modeling H2S solubility in aqueous MDEA, MEA and DEA solutions by the electrolyte SRK-CPA EOS

In this study, an electrolyte cubic plus association equation of state (e-CPA EOS) has been proposed to predict the vapor–liquid equilibrium of (H2S) in aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), and methyldiethanolamine (MDEA). This EOS is composed of repulsive forces, short-range interactions, short-range ionic interactions, association term, long-range ionic interactions, and Born term. The Soave– Redlich– Kwong EOS is used as a non-electrolyte part. A new iterative procedure based on the Jacobi method is introduced to obtain the compositions of all species in the liquid phase. The genetic algorithm (GA) is used to find the optimal values of binary interaction coefficients between molecules and ions. Compared with experimental data, the e-CPA EOS model successfully describes the vapor–liquid equilibrium of H2S in the aqueous solutions of MEA, DEA, and MDEA. The average absolute deviations for 313 data of MEA-H2S-H2O, 156 data of DEA-H2S-H2O, and 145 data of MDEA-H2S-H2O systems were obtained as 8.20 %, 8.04 %, and 9.41 %, respectively. In addition, for some similar cases, the capability of the e-CPA EOS was compared with the Clegg–Pitzer, N-Wilson-NRF, e-NRTL, and e-CTS models. The results indicated that the e-CPA EOS has less error than the four other models.

A new heat transfer model based on non-equilibrium theory for annular flow condensation-part Ⅱ: Ternary zeotropic mixtures

In the past decades, attention has been paid to the flowcondensation heat transfer characteristics of zeotropic mixtures, but most of the research has been carried out on binary mixtures, with very few studies performed on multicomponent mixtures that contain ternary and more components. The condensing process of multicomponent mixtures is significantly more complex since there are interactions between the components except for mixture effects, and these mechanisms are still unclear. Therefore, existing prediction methods either being computationally complicated or fail to accurately describe the condensation characteristics of multicomponent zeotropic mixtures. Focused on this issue, a new heat transfer correlation for ternary zeotropic mixtures in annular flow condensation was proposed based on our previously developed heat transfer model for binary zeotropic mixtures. The ternary mixture is regarded as a combination of two binary mixtures by analyzing the relationship of the condensation rate difference between components and the concentration gradient, and binary interaction coefficients are introduced to estimate the relative contribution of the two independent concentration gradients in the condensing vapor of ternary zeotropic mixtures. The newly developed correlation is simple and agrees well with the condensation heat transfer coefficients of ternary zeotropic mixtures, with an average relative deviation (MRD) of -1.6 %, an average absolute relative deviation (MARD) of 13.9 %, and 90.2 % of the data points falling within ±30 % deviation band for a total of 307 annular flow data.

A Study on Elemental Sulfur Equilibrium Content in Mixtures of Methane, Carbon Dioxide, and Hydrogen Sulfide under Conditions of Natural Gas Pipeline Transmission

The effect of gathering pipeline pressure, temperature, and key components on the solubility of monomeric sulfur in high-sulfur-content natural gas is directly related to the prediction and prevention of sulfur deposition in surface gathering pipelines. Based on our previous study on a prediction model of sulfur solubility in gas with a new formula for the binary interaction coefficient between sulfur and H2S, a new gas–solid thermodynamic phase equilibrium solubility prediction model for monomeric sulfur in high-sulfur-content natural gas was improved based on the gas–solid phase equilibrium principle considering both physical and chemical solution mechanisms. Two new expressions for binary interaction coefficients between sulfur and CO2 and CH4, considering both temperature and solvent density, are proposed in this new solubility prediction model. In this paper, the main factors, such as the gathering pipeline pressure, gathering pipeline temperature, H2S, and CO2, affecting the solubility law of elemental sulfur in high-sulfur-content natural gas are investigated. The results show that the total solubility of elemental sulfur in high-sulfur-bearing natural gas tends to decrease with an increase in the gathering temperature, in which the increase in temperature promotes physical solution, and the physical solution mechanism prevails. Conversely, chemical solution is promoted, and the chemical solution mechanism prevails. With an increase in the gathering pressure, the total solubility of elemental sulfur in high-sulfur-content gas tends to increase, where the physical solubility decreases slightly at first and then increases continuously, with a pressure inflection point of about 2.0 MPa, and the pressure increase has a significant promoting effect on the chemical solubility of elemental sulfur. The increase in the H2S concentration promotes the solution of elemental sulfur in the gas phase in general and significantly promotes the chemical solution of elemental sulfur. The effect on elemental sulfur solubility can be neglected when the molar concentration of CO2 in the gas phase does not exceed 10%.

Experimental determination and thermodynamic optimization of the LiF-NdF3 system.

Neodymium is mainly obtained by electrolysis of a molten LiF-NdF3-Nd2O3 system. LiF-NdF3 is a basic system, and the phase diagram of this system provides important information in the production of electrolytic neodymium. An accurate LiF-NdF3 binary phase diagram helps in the selection of the appropriate molten salt component in production and optimizing the production process, which is of great significance to improve the electrolysis efficiency and reduce the production cost. To obtain an accurate phase diagram of the LiF-NdF3 binary system, liquidus and solidus temperatures were experimentally determined in the LiF-NdF3 binary system by differential scanning calorimetry. The experimental results were used to construct the phase diagram and develop a new database for the LiF-NdF3 system using the FactSage software. The sub-regular solution model was used to describe the excess Gibbs free energy of the liquid phase, and the thermodynamic optimization calculation was carried out for the binary system. The binary interaction coefficients 0L = -39 966 + 17.68 T, 1L = -7667 + 26.1 T, and 2L = -6000 were used to describe the system's excess Gibbs free energy. The results show that the eutectic point of the system is 68.4% LiF-31.6% NdF3 at 731.5 °C. The effects of industrial and high purity NdF3 and the presence of Nd2O3 on the liquidus temperature of the LiF-NdF3 system were also investigated, high liquidus temperatures have been observed in tests using industrial NdF3 and NdF3 feedstock that contains a specific quantity of Nd2O3.

The state of the art of cubic equations of state with temperature-dependent binary interaction coefficients: From correlation to prediction

Cubic equations of state (CEoSs) are extensively used in academia and industry for their consistency, reliability, even under extrapolation conditions, and capacity to predict phase-equilibrium and energetic properties with acceptable accuracy. The optimal parametrization of a pure-component CEoS, a prerequisite for the development of any CEoS for mixtures, is discussed first. The binary interaction parameter (BIP) involved in the Van der Waals mixing rules of CEoSs is introduced with special attention to the temperature-dependent functions used to express it. The following questions are addressed: what is the physical meaning of the BIP? How does this parameter reveal deviations from ideal mixtures? What are the connections between Van der Waals and advanced (EoS/gE) mixing rules? What are the best methods to correlate this parameter? How can we predict it? In conclusion, the limitations and performances of models involving Van der Waals mixing rules, including BIPs, are examined and compared to the CEoSs based on advanced mixing rules.

Assessment of the applicability of binary mixture hypothesis to modeling the phase behavior of heavy oil/bitumen-solvent systems for EOR applications

Conventional production methods in heavy oil reservoirs are not efficient primarily due to the high viscosity of the oil. Several methods such as VAPEX and ES-SAGD have been developed to overcome production challenges from these reservoirs, which mainly rely on oil viscosity reduction. Solvent injection dilutes the oil and produces a complex asymmetric mixture. It is difficult to study the phase behavior of oil due to the diversity of its components, and it gets more complicated with the addition of solvent. One of the assumptions to simplify the problem is considering heavy oil as a single pseudo component and investigating the thermophysical properties of binary mixtures with diluents. This study collected and evaluated more than 1000 experimental data on various types of heavy oil/bitumen and several hydrocarbon and non-hydrocarbon solvents. The data were divided into two groups, below and above the critical temperature of the solvent, according to experimental temperatures. Modeling of mixture phase behavior as a binary mixture was performed using the advanced Peng-Robinson equation of state (APR-EoS). EoS tuning to match the experimental data was performed by optimizing the binary interaction coefficients (kij). The results showed that the binary mixture assumption could be used as a practical approach to construct pressure-composition phase diagrams. Optimized values of kij were proposed as two empirical correlations according to the dimensionless ratio Tco/Tcs (oil critical temperature to solvent critical temperature). The model constructed using these correlations showed an average deviation of about 16% compared to experimental data. It is necessary to note that the vapor-liquid-liquid three-phase regions may occur in a heavy oil/bitumen and solvent mixture. But according to the Gibbs phase rule, with two components and three phases in the system, the degree of freedom equals one. So, investigating the effects of pressure change on three-phase regions is not possible using this model.

Improving water–hydrocarbon equilibrium calculations using multi objective optimization

The addition of chemical terms to Cubic Equations of State to improve polar components Vapor–Liquid Equilibrium prediction overestimates the critical point. In this paper, we analyze the mathematical behavior of these equations and propose a new methodology based on multi-objective optimization with four independent functions, saturation pressure, saturated liquid volume, and two critical points constraints to estimate the pure component parameters for the equation of state. The effect of different parameters sets on the phase equilibrium prediction and binary interaction coefficient for some binary water–hydrocarbon systems is presented and discussed, showing the improvement of the proposed technique.

Empirical Correlations for K-Values of Crude Oils

Based on the Soave–Redlich–Kwong equation of state, empirical correlations for the K -values of N 2 , CO 2 , H 2 S , C 1 , and C 2 are proposed. Complementarily, the binary interaction coefficients involving the plus fraction, C 7 + , were optimized by fitting into 131 experimental data from the literature. The criterion to select the form of the empirical correlations was based on the identification of the major dependencies of the equilibrium constants on the system variables (e.g., pressure, temperature, and composition). For most of the experimental data, the saturation pressure calculated via the empirical correlations is in excellent agreement with those reported from the laboratory. The empirical correlations cover a variety of temperatures (128–314°F), pressures (313–6880 psi), and compositions (N2: 0.0–1.67%; CO2: 0.0–9.11%; H2S: 0.0–3.68%; C1: 5.63–74.18%; C2: 0.84–12.45%; C7+: 10.72–83.2%). The proposed correlations are useful for rapid vapor-liquid equilibrium calculations during the compositional modeling of petroleum reservoirs.

Thermodynamic modeling of hydrogen–water systems with gas impurity at various conditions using cubic and PC-SAFT equations of state

Hydrogen (H2) has emerged as a viable solution for energy storage of renewable sources, supplying off-seasonal demand. Hydrogen contamination due to undesired mixing with other fluids during operations is a significant problem. Water contamination is a regular occurrence; therefore, an accurate prediction of H2-water thermodynamics is crucial for the design of efficient storage and water removal processes. In thermodynamic modeling, the Peng–Robinson (PR) and Soave Redlich–Kwong (SRK) equations of state (EoSs) are widely applied. However, both EoSs fail to predict the vapor-liquid equilibrium (VLE) accurately for H2-blend mixtures with or without fine-tuning binary interaction parameters due to the polarity of the components. This work investigates the accuracy of two advanced EoSs: the Schwartzentruber and Renon modified Redlich–Kwong cubic EoS (SR-RK) and perturbed-chain statistical associating fluid theory (SAFT) in predicting VLE and solubility properties of H2 and water. The SR-RK involves the introduction of polar parameters and a volume translation term. The proposed workflow is based on optimizing the binary interaction coefficients using regression against experimental data that cover a wide range of pressure (0.34 to 101.23 MPa), temperature (273.2 to 588.7 K), and H2 mole fraction (0.0004 to 0.9670) values. A flash liberation model is developed to calculate the H2 solubility and water vaporization at different temperature and pressure conditions. The model captures the influence of H2-gas (CO2) impurity on VLE. The results agreed well with the experimental data, demonstrating the model’s capability of predicting the VLE of hydrogen-water mixtures for a broad range of pressures and temperatures. Optimized coefficients of binary interaction parameters for both EoSs are provided. The sensitivity analysis indicates an increase in H2 solubility with temperature and pressure and a decrease in water vaporization. Moreover, the work demonstrates the capability of SR-RK in modeling the influence of gas impurity (i.e., H2–CO2 mixture) on the H2 solubility and water vaporization, indicating a significant influence over a wide range of H2–CO2 mixtures. Increasing the CO2 ratio from 20% to 80% exhibited almost the opposite behavior of H2 solubility compared to the pure hydrogen feed solubility. Finally, the work emphasizes the critical selection of proper EoSs for calculating thermodynamic properties and the solubility of gaseous H2 and water vaporization for the efficient design of H2 storage and fuel cells.

GAS-CONDENSATE FLUID PVT MODEL QUALITY CHECK BASED ON THE CONCEPT OF A SINGLE-CELL SIMULATION MODEL

The problems of gas-condensate PVT-models (Pressure Volume Temperature, PVT) creation under limited input information were analyzed. Traditional fluid phase behavior characterization approach relies on creation of the equation of state (EOS) based on initial composition of reservoir fluid and its future regression for critical parameters (pressure and temperature), binary interaction coefficients, acentric factors of residual “plus” fraction or pseudo-components. The adjustment is done until the moment when EOS is reproducing the results of laboratory experiments. Classic PVT experiments performed on gas-condensates and volatile oils are constant composition expansion (CCE), constant volume depletion (CVD) and separator tests. However, in the case of most Ukrainian fields, discovered and explored in the last century, not only the reliable detailed initial fluid composition is not available, but phase behavior was studied with non-equilibrium method of so-called differential condensation, that does not allow their direct application for PVT models creation. Previously, the authors [1, 2] presented an alternative method for fluid characterization based on the fractional distillation test. At the same time, due to significant uncertainty in input data, particularly a) condensate production allocation; b) commingled production from multiple reservoirs with different C5+ yield; c) non-recorded change of separator conditions that affects liquid extraction and its density; d) technological production losses, issues of reproducing the condensate production during history matching of several models of Dniper-Donetsk Basin were faced. There was proposed and explained in detail an example of single-cell reservoir simulation model application concept for quality check of created PVT model for one of the fields with potential yield of 86 g/m3. The idea of the concept is based on the reproduction of material balance of gas-condensate reservoir through one conditional well controlled on a primary (gas) phase, that allows quick identification of changes into calculated gas-condensate yield curve, necessary for matching of condensate production. Implementation of these changes allows quick and precise full-field model calibration.

Experimental measurement and model prediction of solid-liquid equilibrium for methane-ethane binary system

Solid-liquid equilibrium characteristics of light alkane mixtures are of great significance for their applications in chemical engineering and liquified natural gas industry. However, the related researches, especially on their eutectic characteristics and phase change behaviors, are insufficient. Therefore, in the present study, a test rig with a temperature preparing capacity below 70 K is built to measure the freezing point temperatures of different methane-ethane mixture samples. Fifteen experimental points are obtained from the tests in which the freezing temperature varies from 73.88 K to 90.65 K and the molar fraction of methane changes from 0 to 1. Three models are utilized to predict the solid–liquid equilibrium of methane-ethane binary system, and the comparison study shows that SRK model reaches the most accuracy with a relative standard deviation of 1.27%. Based on the data regression of experimental results, the binary interaction coefficient with k12 = -0.073 instead of k12 = 0 is recommended in the prediction of SLE of methane-ethane binary system. Furthermore, a cubic polynomial formula is proposed to corelate k12 variation with temperature, and the modified SRK model with temperature-dependent k12 gives a more accurate prediction on the SLE of methane-ethane binary system with the standard deviation of 0.99%. The predicted eutectic temperature of methane-ethane binary system by the modified model is about 72.71 K and the corresponding methane molar fraction is about 0.668, which are closer to the test data.

Vapor-liquid equilibrium (VLE) prediction for dimethyl ether (DME) and water system in DME injection process with Peng-Robinson equation of state and composition dependent binary interaction coefficient

Dimethyl ether (DME) is arousing attention as a novel water-soluble additive in oil industry. The accurate prediction of phase behavior of DME and water system is crucial important for DME-based research. An equation of state has been a powerful tool for solving phase equilibrium problem, which is based on an ideal molecular force model with binary interaction coefficients reflecting the deviation of a non-ideal system. However, the current knowledge of interaction coefficient is limited by obtaining from backward by using phase equilibrium data. This leads to the unclear meaning of the interaction coefficients, insufficient response to the molecular force interaction relationship at the molecular level and no ability to predict phase equilibrium properties without primary use of experimental data. To overcome this, in this study a correction by combining an activity coefficient and a linear solvation energy relationship (LSER) has been proposed to address the solubility deviation from an idealized model. This deviation at the micro level indicates the deviation of nonideal molecular forces from the ideal Raoult's law. Based on this novel correction, binary interaction coefficients have been obtained with a more practical molecular interaction relationship, which leads to more consistent results with experimental data from the literature. Moreover, in asymmetric phase systems, concentration-dependent binary interaction coefficients have been proposed based on previous discussion to represent intermolecular forces in non-ideal phase systems. Furthermore, partitioning coefficients, which lead to a potential criterion for solvent selection for heavy oil recovery, have been discussed from the perspective of intermolecular forces. This study provides new insights into non-ideal phase behavior. By combining a LSER and activity coefficients, a quantitative analysis on non-ideal molecular behavior and related complex phase problems becomes possible.

Investigation of drying the porous wood of a cylindrical shape

In the presented study, the mathematical model for drying the porous timber beam of a circular cross-section under the action of a convective-heat nonstationary flow of the drying agent is constructed. When solving the problem, a capillary-porous structure of the beam is described in terms of a quasi-homogeneous medium with effective coefficients, which are chosen so that the solution in a homogeneous medium coincides with the solution in the porous medium. The influence of the porous structure is taken into account by introducing into the Stefan–Maxwell equation the effective binary interaction coefficients. The problem of mutual phase distribution is solved using the principle of local phase equilibrium. The given properties of the material (heat capacity, density, thermal conductivity) are considered to be functions of the porosity of the material as well as densities and heat capacities of body components. The solution is obtained for determining the temperature in the beam at an arbitrary time of drying at any coordinate point of the radius, thermomechanical characteristics of the material, and the parameters of the drying agent.

An effective procedure for wax formation modeling using multi-solid approach and PC-SAFT EOS for petroleum fluids with PNA characterization

Several experiments and thermodynamic models are developed to prevent Wax precipitation. Paraffinic hydrocarbons participate to a greater extent in the precipitation process than other hydrocarbon families. However, the existing models do not distinguish these hydrocarbon families, leading to the overestimation or underestimation of wax precipitation parameters. To address this problem, we will use a predictive Paraffin, Naphthene, and Aromatic (PNA) estimation technique to split the petroleum fractions that avoids using average properties for petroleum fractions. A sequential multi-solid approach is also implemented for the thermodynamic analysis of wax precipitation. The perturbed chain statistical associating fluid theory (PC-SAFT) equation of state (EOS) is utilized to calculate liquid properties. The binary interaction coefficients (BIC) of non-paraffin hydrocarbons are modified to improve the model's accuracy for calculating wax weight and wax appearance temperature (WAT). Six crudes from the North Sea are selected to evaluate the reliability of the proposed model. The contribution of each hydrocarbons family in the precipitation process is investigated. The results show a considerable improvement compared to previous models. The predicted WAT presents a slight deviation from the experimental data. In addition, the outcome of this work is compared to the modeling works from two reliable references. The average estimation error of wax weight for all crude oils is about 0.19. This deviation increases to 0.36 and 0.38 for the works of the first and second reference, in turn.

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information

The complexation of Np(V) with malonate and succinate is studied by different spectroscopic techniques, namely, attenuated total reflection Fourier transform infrared (ATR FT-IR) and extended X-ray absorption fine-structure (EXAFS) spectroscopy, as well as by quantum chemistry to determine the speciation, thermodynamic data, and structural information of the formed complexes. For complex stoichiometries and the thermodynamic functions (log βn°(Θ), ΔrHn°, ΔrSn°), near infrared absorption spectroscopy (vis/NIR) is applied. The complexation reactions are investigated as a function of the total concentration of malonate ([Mal2-]total) and succinate ([Succ2-]total), ionic strength [Im = 0.5-4.0 mol kg-1 Na+(Cl-/ClO4-)], and temperature (Θ = 20-85 °C). Besides the solvated NpO2+ ion, the formation of two Np(V) species with the stoichiometry NpO2(L)n1-2n (n = 1, 2, L = Mal2-, Succ2-) is observed. With increasing temperature, the molar fractions of both complex species increase and the temperature-dependent conditional stability constants log βn'(Θ) at given ionic strengths are determined by the law of mass action. The log βn'(Θ) are extrapolated to IUPAC reference-state conditions (Im = 0) according to the specific ion interaction theory (SIT), revealing thermodynamic log βn°(Θ) values. For all formed complexes, [NpO2(Mal)-: log β1°(25 °C) = 3.36 ± 0.11, NpO2(Mal)23-: log β2°(25 °C) = 3.95 ± 0.19, NpO2(Succ)-: log β1°(25 °C) = 2.05 ± 0.45, NpO2(Succ)23-: log β2°(25 °C) = 0.75 ± 1.22], an increase of the stability constants with increasing temperature was observed. This confirmed an endothermic complexation reaction. The temperature dependence of the log βn°(T) values is described by the integrated Van't Hoff equation, and the standard reaction enthalpies and entropies for the complexation reactions are determined. Furthermore, the sum of the specific binary ion-ion interaction coefficients Δεn°(Θ) for the complexation reactions are obtained as a function of the t from the respective SIT modeling as a function of the temperature. In addition to the thermodynamic data, the structures of the complexes and the coordination modes of malonate and succinate are investigated using EXAFS spectroscopy, ATR-FT-IR spectroscopy, and quantum chemical calculations. The results show that in the case of malonate, six-membered chelate complexes are formed, whereas for succinate, seven-membered rings form. The latter ones are energetically unfavorable due to the limited space in the equatorial plane of the Np(V) ion (as NpO2+ cation).

Compositional modeling of multicomponent gas injection into saline aquifers with the MUFITS simulator

Reservoir simulations of the co-injection of natural gas, carbon dioxide, and other non-condensable gases into saline aquifers are in demand in many areas of subsurface utilization, ranging from excess energy and greenhouse gas storage to the substitution of cushion gas with CO2. We aim at extending our reservoir simulator MUFITS for modeling flows in porous media related to these applications. For the accurate prediction of phase equilibria in aqueous systems, we implement a modified method of Søreide and Whitson in the compositional module of the software. The modified equation of state (EoS) involves the most recent literature data on the binary interaction coefficients and several new correlations for volume shifts to improve the accuracy of the EoS for predicting the partial volume of dissolved gases. All the aggregated and developed correlations are built into the simulator to facilitate its usage by the scientific community. The extended software is validated against a benchmark study of pure CO2 injection into a saline aquifer. Furthermore, two more complicated studies concerning the co-injection of several gases are conducted to demonstrate the potential application areas of MUFITS. First, we simulate the injection of impure carbon dioxide into an aquifer and briefly discuss the influence of N2 impurity on the propagation of the gas plume. We show that the plume is significantly wider in the case of impure CO2 injection. Second, we simulate the injection of supercritical CO2 into a synthetic natural gas storage reservoir to substitute cushion gas. We show that the mechanical dispersion can cause a rapid CO2 spread into the wells used for natural gas production.

GAS-CONDENSATE FLUID PVT MODEL QUALITY CHECK BASED ON THE CONCEPT OF A SINGLE-CELL SIMULATION MODEL

The problems of gas-condensate PVT-models (Pressure Volume Temperature, PVT) creation under limited input information were analyzed. Traditional fluid phase behavior characterization approach relies on creation of the equation of state (EOS) based on initial composition of reservoir fluid and its future regression for critical parameters (pressure and temperature), binary interaction coefficients, acentric factors of residual “plus” fraction or pseudo-components. The adjustment is done until the moment when EOS is reproducing the results of laboratory experiments. Classic PVT experiments performed on gas-condensates and volatile oils are constant composition expansion (CCE), constant volume depletion (CVD) and separator tests. However, in the case of most Ukrainian fields, discovered and explored in the last century, not only the reliable detailed initial fluid composition is not available, but phase behavior was studied with non-equilibrium method of so-called differential condensation, that does not allow their direct application for PVT models creation. Previously, the authors [1, 2] presented an alternative method for fluid characterization based on the fractional distillation test. At the same time, due to significant uncertainty in input data, particularly a) condensate production allocation; b) commingled production from multiple reservoirs with different C5+ yield; c) non-recorded change of separator conditions that affects liquid extraction and its density; d) technological production losses, issues of reproducing the condensate production during history matching of several models of Dniper-Donetsk Basin were faced. There was proposed and explained in detail an example of single-cell reservoir simulation model application concept for quality check of created PVT model for one of the fields with potential yield of 86 g/m3. The idea of the concept is based on the reproduction of material balance of gas-condensate reservoir through one conditional well controlled on a primary (gas) phase, that allows quick identification of changes into calculated gas-condensate yield curve, necessary for matching of condensate production. Implementation of these changes allows quick and precise full-field model calibration.