Flash Calculations Research Articles

Effect of Pore Size Heterogeneity on Hydrocarbon Fluid Distribution, Transport, and Primary and Secondary Recovery in Nano-Porous Media

In this paper, we investigate the effect of pore size heterogeneity on fluid composition distribution of multicomponent-multiphase hydrocarbons and its subsequent influence on mass transfer in shale nanopores. The change of multi-contact minimum miscibility pressure (MMP) in heterogeneous nanopores was investigated. We used a compositional simulation model with a modified flash calculation, which considers the effect of large gas–oil capillary pressure on phase behavior. Different average pore sizes for different segments of the computational domain were considered and the effect of the resulting heterogeneity on phase change, composition distributions, and production was investigated. A two-dimensional formulation was considered here for the application of matrix–fracture cross-mass transfer and the rock matrix can also consist of different segments with different average pore sizes. Both convection and molecular diffusion terms were included in the mass balance equations, and different reservoir fluids such as ternary mixture syntactic oil, Bakken oil, and Marcellus shale condensate were considered. The simulation results indicate that oil and gas phase compositions vary in different pore sizes, resulting in a concentration gradient between the two adjacent pores of different sizes. Given that shale permeability is extremely small, we expect the mass transfer between the two sections of the reservoir/core with two distinct average pore sizes to be diffusion-dominated. This observation implies that there can be a selective matrix–fracture component mass transfer as a result of confinement-dependent phase behavior. Therefore, the molecular diffusion term should be always included in the mass transfer equations, for both primary and gas injection enhanced oil recovery (EOR) simulation of heterogeneous shale reservoirs.

Drawing PT-phase envelopes and calculating critical points for multicomponent systems using flash calculations

Objectives. This study aims to draw PT-phase envelopes and calculate the critical points for multicomponent systems using flash calculations.Methods. Flash calculations with an equation of state and a mixing rule were used to construct phase envelopes for multicomponent systems. In general, the methodology uses the Soave–RedlichKwong equation of state and Van der Waals mixing rules; and the Peng–Robinson equation of state with Wong–Sandler mixing rules and the non-random two-liquid activity coefficient model.Results. The method was applied to the following mixtures: ethane (1)–butane (2) (four different compositions); ethane (1)–propane (2) (four different compositions); butane (1)–carbon dioxide (2) (three different compositions); C2C3C4C5C6 (one composition); isobutane–methanol–methyl tertbutyl ether–1-butene (one composition); and propylene–water–isopropyl alcohol–diisopropyl ether (one composition).Conclusions. Our results agreed to a large extent with the experimental data available in the literature. For mixtures that contained CO2 , the best results were obtained using the PengRobinson equation of state and the Wong–Sandler mixing rules. Our methodology, based on flash calculations, equations of state, and mixing rules, may be viewed as a shortcut procedure for drawing phase envelopes and estimating critical points of multicomponent systems.

A Review of the Latest IEEE 1584 and How This Affects You

The IEEE 1584 standard is a widely used guideline for performing arc flash calculations developed by IEEE. The standard was initially released in 2002 to estimate the incident energy and has been the cornerstone of many arc flash studies for more than a decade. A major update released in November 2018 overhauls the incident energy equations and takes into account the equipment enclosure dimensions and electrode orientation in the calculation. The new equations were empirically derived from more than 1800 tests and is a vast development from the initial standard which tested for only 300 cases.

Ammonia/Ethanol Mixture for Adsorption Refrigeration

Adsorption refrigeration has become an attractive technology due to the capability to exploit low-grade thermal energy for cooling power generation and the use of environmentally friendly refrigerants. Traditionally, these systems work with pure fluids such as water, ethanol, methanol, and ammonia. Nevertheless, the operating conditions make their commercialization still unfeasible, especially owing to safety and cost issues as a consequence of the working pressures, which are higher or lower than 1 atm. The present work represents the first thermodynamic insight in the use of mixtures for adsorption refrigeration and aims to assess the performance of a binary system of ammonia and ethanol. According to the Gibbs’ phase rule, the addition of a component introduces an additional degree of freedom, which allows to adjust the pressure of the system varying the composition of the mixture. The refrigeration process was simulated with isothermal- isochoric flash calculations to solve the phase equilibria, described by the Peng-Robinson-Stryjek-Vera (PRSV) equation of state for the vapor and liquid phases and by the ideal adsorbed solution theory (IAST) and the multicomponent potential theory of adsorption (MPTA) for the adsorbed phase. In operating condenser and evaporator, pressure levels around atmospheric pressure can be achieved using an ammonia/ethanol mixture with a mole fraction of ethanol in the range of 0.70−0.75. A good agreement in the predictions of the adsorbed phase composition was also reported using the IAST and the MPTA methods.

Estimation of PC-SAFT binary interaction coefficient by artificial neural network for multicomponent phase equilibrium calculations

Perturbed-Chain Statistical Associating Fluid Theory Equation of State (PC-SAFT EoS) requires cross interaction parameter for each binary pair in the mixture. For real mixtures, these parameters should be corrected by binary interaction coefficients (kij's). The values of kij's are tuned by an optimization method in order to minimize the deviation from equilibrium data. The Particle Swarm Optimization (PSO) algorithm is employed for optimization of kij's due to the continuous nature of kij and highly nonlinear nature of PC-SAFT EoS. Although kij can be adjusted using the mentioned algorithm, it is cumbersome and highly time-consuming because the optimization should be performed for each pair that exists in the multicomponent mixture. It has been shown that these optimal values can be obtained based on the basic characteristic properties of the participating molecules in each pair, this is particularly useful to avoid solving any optimization problem. Furthermore, Artificial Neural Networks (ANNs) as powerful function approximators have been used to predict binary interaction coefficients based on basic characteristic properties of molecules that exist in each pair. Two types of characteristic properties have been examined as inputs of the ANN's utilized to predict the optimum kij's. The first one contains PC-SAFT parameters (m, ε/k, σ) and molecular weight of each component; while the second category contains specific gravity, normal boiling point and molecular weight of each component.The best structure of ANN has been obtained by two approaches: 1) Genetic Algorithm (GA) and 2) a constructive approach. GA can find the structure with any possible connections between neurons whereas the constructive approach can only find the best structure for fully connected networks. The results show that the genetically designed ANN that uses the second set of inputs outperforms the others. This ANN is used to estimate kij's of PC−SAFT for a wide range of non-associating materials where the predicted kij's are in close agreement with those obtained by PSO with coefficient of determination R2 = (0.9921, 0.9631) for training and validation data, respectively. In addition to the evaluation of the ANN by validation data, its performance has been examined by using its estimated kij's in flash calculation of a synthesized multi-component mixture and bubble point calculation of a reservoir fluid. Comparing the results of equilibrium calculations with their experimental counterparts shows that they closely follow the measured data. Furthermore, its performance has been compared with other approaches of estimation of kij such as London theory and QSPR method and the results show that the proposed ANN outperforms the others.

Reducing HCl Release to the Environment by Eliminating Methyl Chloride at Reactors End of Run

Study of unreacted MeCl clearing from CSTR reactors at the end of run: It is a unique set up with CSTR reactors in cascade, used to produce salt-based product, esters and methanol from this unit operations. This study involves chemical reaction Engineering and process improvement experiments along with control logics to perform the steps to eliminating MeCl to the environment either in vapor or liquid form. pH and agitation speed are critical criterion to determine the presence of MeCl in the final drained liquid after the end of run. Process trends have been depicted in the study to verify the authenticity of the steps followed. Practical methods have been run through the lab analysis as well as studies done through the real unit operations environment. Reaction calculation was also part of methods used to conclude some portion of the study. Most literatures were referred through MeCl thermal and physical property data through published safety data sheets and pending patents on scrubbing methods of MeCl. Data was also collected through lab analysis on GC spectrometry with both gas and liquid methods, collected reading from unit operations at different ranges of pressure profile. This discussion would involve the use of water and caustic wash to react most of the MeCl out. The point in question is to minimize or eliminate of HCl emissions generated through unreacted MeCl when reactors are at the end of run and eventually getting washed off. Study concludes by giving quantity of MeCl (eventually HCl) sent to flare or thermal oxidizer to eventually burn-out. Recommendations were made with respect to number of cycles of wash to minimize the inert levels, thermal efficiency improvement to crack down the MeCl down that will be burned as well as changes in handling the unit operations. Conclusions are based on flash calculations, chemical reaction between Caustic, Water and MeCl + heat through steam jackets with combinations of pressure and temperature changes. Results published with the successful run of the process that is being recommended through the study.

High-Resolution Inline Density Measurements: Insight on Multiphase Flow and Transport Phenomena in Porous Media

Understanding fluid flow in porous media is essential with complex and multiphase fluid flow. We demonstrate that high-resolution in-line density measurements are a valuable tool in this regard. An in-line densitometer is used in fluid flow in porous media applications to quantify fluid production and obtain quantitative and qualitative information such as breakthrough times, emulsion/foam generation, and steam condensation. In order to determine the potential applications for in-line densitometry for fluid flow in porous media, a series of sand pack floods were performed with a densitometer placed at the outlet of a sand pack. All fluids passed through the measurement cell at experiential temperatures and pressures. An algorithm was developed and applied to the density data to provide a quantitative determination of oil and water production. The second series of tests were performed at high temperature and pressure, with a densitometer placed at the inlet and outlet of a sand pack, for steam applications. In both series of experiments, data acquisition was collected at 1 hertz and the analyzed density data was compared to results from the conventional effluent analysis, including Dean-Stark, toluene separations, magnetic susceptibility measurement, and flash calculations where applicable. The high-resolution monitoring of effluent from a flow experiment through porous media in a system with two phases of known densities enables two-phase production to be accurately quantified in the case of both light and heavy oil. The frequency of measurements results in a high-resolution history of breakthrough times and fluid behavior. In the case of monitoring steam injection processes, reliable laboratory tests show that in-line density measurements enable the determination of steam quality at the inlet and outlet of a sand pack and qualitative determination of steam condensation monitoring The use of in-line densitometry provides insight on the monitoring of complex fluid flow in porous media, which typical bulk effluent analysis is not able to do. The ability to measure produced fluids at high resolution and extreme temperatures reduces mass balance error associated with the effluent collection and broadens our understanding of complex fluid flow in porous media.

Improved Multiple-Mixing-Cell Method for Accelerating Minimum Miscibility Pressure Calculations

Summary An improved algorithm for accelerating minimum miscibility pressure (MMP) computation using the multiple-mixing-cell (MMC) methods is presented. The MMC method is widely used to accurately calculate the MMP. In this study, we proposed an acceleration algorithm toward original MMC method to directly locate the shortest key tie-line (TL) after a certain amount of contacts through the adjustment of the gas/oil mixing ratio during the calculation process. The algorithm contains the following key components: (1) mixing cell cutoff strategy to avoid unnecessary flash calculations; (2) gas/oil mixing ratio adjustment to prevent lost information on the shortest key TL during the cell cutoff process; (3) a search algorithm for pressure to improve the next step pressure estimate; (4) the fast and reliable two-phase flash implementation by combining full Newton method with recently proposed iteration variables and conventional successive substitution method. The improved MMC model is shown to be faster than the original MMC method in computing MMP.

A black-oil approach to model produced gas injection in both conventional and tight oil-rich reservoirs to enhance oil recovery

A robust compositionally extended black-oil simulation approach is developed, which is capable of including the effect of large gas-oil capillary pressure for first contact miscible (FCM), and immiscible gas injection. The simulation methodology is applied to gas flooding in both high and very low permeability reservoirs. For a high permeability conventional reservoir, simulations use a five-spot pattern with different reservoir pressures to mimic both FCM and immiscible displacements. The results show that the simple modified black-oil approach can model well both immiscible and miscible floods, as long as the minimum miscibility pressure (MMP) is matched. For a tight oil-rich reservoir, primary depletion and huff-n-puff gas injection are simulated including the effect of large gas-oil capillary pressure in flow and in flash calculation on recovery. Finally, a dynamic gas-oil relative permeability correlation that accounts for the compositional changes owing to the produced gas injection is introduced and applied to correct for changes in interfacial tension (IFT), and its effect on oil recovery is examined. The results show that the new black-oil approach can model these processes well and could be implemented when fully compositional simulations are computationally too time consuming. For the first time, a black-oil type reservoir simulation method is used to simulate near-miscible and immiscible produced gas injection enhanced oil recovery. It provides a fast and robust alternative for large-scale reservoir simulation with the purpose of flaring/venting reduction through reinjecting the produced gas into the reservoir for EOR.

Experimental study and thermodynamic modeling of clathrate hydrate stability conditions in carbon dioxide + cyclopentane + water system: Retrograde region

In this study, hydrate dissociation conditions for the carbon dioxide + cyclopentane + water system were measured. The pressure-search method at constant volume was employed to measure equilibrium conditions in the temperature range from 287.4–293.1 K and pressure range from 0.99–4.78 MPa. The results exhibit a retrograde behavior at pressures above 4 MPa for this system. Also, the experiments show that cyclopentane would significantly promote carbon dioxide hydrate stability conditions. In addition, based on the minimization of Gibbs free energy, a multiphase flash calculation was performed using the van der Waals and Platteeuw (vdW-P) solid solution theory along with the cubic plus association (CPA) equation of state to predict gas hydrate stability conditions. Modeling results are found in good agreement with the experimental data even in the retrograde region.

CFD modeling of industrial cold box with plate-fin heat exchanger: Focusing on phase change phenomenon

Cold box with plate-fin heat exchanger (PFHE) is extensively used in liquefied natural gas (LNG) refinery plants. In the present study, a CFD model in ANSYS FLUENT is developed for better understanding the transport phenomena, especially the phase change, in a quite complex plate-fin heat exchanger operated in a gas refining company. The flow channels, ducts and passes of the cold box, are considered in the computational geometry. The porous media technique is introduced in the computational domain due to the excessive increase in the number of computational grids when the fins accounted for in the numerical domain. The flash calculations (FC) technique is coupled with CFD in evaluation of chemical species in the cold box by a user defined function. This study examines the importance of local thermal equilibrium between the porous medium and fluid flow without mass transfer (LTE-non mass), local thermal equilibrium between the porous medium and fluid flow with mass transfer (LTE), and local thermal non equilibrium between the porous medium and fluid flow with mass transfer (LTNE) in simulation of an industrial cold box. Numerical results are compared with the corresponding operational data and the best agreement is obtained by the LTNE approach. The calculated mean relative errors of the LTNE approach for the outlet vapor fraction of streams A, hot stream, B and C, sided cold streams, are 0.15, 0.352, and 0.173%, respectively.

Comprehensive Overview and Comparison of ANSI Versus IEC Short-Circuit Calculations: Using IEC Short-Circuit Results in IEEE 1584 Arc Flash Calculations

In this paper, we review both ANSI/IEEE and IEC short-circuit calculation methods. We discuss and compare terminology, definitions, and calculation approaches. The advantages and disadvantages of both standards with numerical examples are presented. Identical systems are analyzed using both methods to make a side-by-side comparison of the results. After both methods are introduced in detail and understood, arc flash calculation examples will be provided using IEC short-circuit calculations. Currently, all arc flash calculation methods (including IEEE 1584) focus on three-phase fault currents without being limited to any specific short-circuit standard. In our approach, the IEC method can be effectively used for arc calculations. This approach can be utilized in regions of the world where IEC standards are used for short-circuit calculations.

A Continuous and Predictive Viscosity Model Coupled to a Microemulsion Equation of State

SummarySurfactant floods can attain high oil recovery if optimal conditions with ultralow interfacial tensions (IFT) are achieved in the reservoir. A recently developed equation-of-state (EoS) phase-behavior net-average-curvature (NAC) model based on the hydrophilic-lipophilic difference (HLD-NAC) has been shown to fit and predict phase-behavior data continuously throughout the Winsor I, II, III, and IV regions. The state-of-the-art for viscosity estimation, however, uses empirical nonpredictive based on of fits to salinity scans, even though other parameters change, such as the phase number and compositions. In this paper, we develop the first-of-its-kind microemulsion viscosity model that gives continuous viscosity estimates in composition space. This model is coupled to our existing HLD-NAC phase-behavior EoS.The results show that experimentally measured viscosities in all Winsor regions (two- and three-phase) are a function of phase composition, temperature, pressure, salinity, and the equivalent alkane carbon number (EACN). More specifically, microemulsion viscosities associated with the three-phase invariant point have an M shape as formulation variables change, such as from a salinity scan. The location and magnitude of viscosity peaks in the M are predicted from two percolation thresholds after tuning to viscosity data. These percolation thresholds as well as other model parameters change linearly with EACN and brine salinity. We also show that the minimum viscosity in the M shape correlates linearly with EACN or the viscosity ratio. Other key parameters in the model are also shown to linearly correlate with the EACN and brine salinity. On the basis of these correlations, two- and three-phase microemulsion viscosities are determined in five-component space (surfactant, two brine components, and two oil components) independent of flash calculations. Phase compositions from the EoS flash calculations are entered into the viscosity model. Fits to experimental data are excellent, as well as viscosity predictions for salinity scans not used in the fitting process.

Impact of fluid property shift and capillarity on the recovery mechanisms of CO2injection in tight oil reservoirs

AbstractThe phase equilibria with the confinement effect could shift in nano‐pores, which could have a great impact on the recovery mechanisms of CO2injection in tight oil reservoirs; this has not been systematically studied. In this paper, the confinement effect with property shift and capillarity effect is introduced into the flash calculation of confined fluids. The Soave modification of the Redlich–Kwong equation of state is extended by the molecular‐wall collision parameter to describe the shifted pressure–volume–temperature properties of confined fluid, and the Young–Laplace equation is applied to evaluate the capillary pressure. This developed model could effectively be applied for phase equilibrium calculation in tight porous media because of the verification of experimental results. A binary mixture is investigated to study the different effect of capillary pressure and property shift on phase equilibria. Subsequently, a typical hydrocarbon fluid from Middle Bakken tight oil reservoirs is studied with CO2injection. Results illustrate that the confinement effect could play an increasingly important part in the phase equilibrium state. The CO2solubility and mass transfer driving force in tiny pores would be greater than those in large pores under the same conditions. The gas phase saturation would be smaller with the same compositions, which could extend the single‐phase region of fluid flow in porous media. Furthermore, bubble‐point pressure, the minimum miscible pressure of CO2/hydrocarbon, and the viscosity of tight oil dissolved with CO2both decrease with the pore size, which has a good influence on tight oil recovery. In general, the confinement effect could effectively reinforce the recovery mechanisms of CO2injection, which is conducive to the enhancement of tight oil recovery. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Robust Three-Phase Vapor–Liquid–Asphaltene Equilibrium Calculation Algorithm for Isothermal CO2 Flooding Applications

CO2 flooding is an effective enhanced oil recovery process for light oil reservoirs. Asphaltenes can easily precipitate during CO2 flooding, leading to the appearance of three-phase vapor–liquid–asphaltene (VLS) equilibria. A prerequisite for accurately simulating the CO2 flooding process is developing a robust three-phase VLS equilibrium calculation algorithm. In this study, we develop a robust and efficient three-phase VLS equilibrium calculation algorithm with the use of asphaltene precipitation model proposed by Nghiem et al. [ Efficient Modelling of Asphaltene Precipitation, SPE, 1993]. To develop this algorithm, a two-phase flash calculation algorithm is first developed to split the mixture into an asphaltene phase and a nonasphaltene phase. Moreover, two different three-phase VLS flash calculation algorithms are developed and incorporated into our three-phase equilibrium calculation algorithm. New initialization approaches for both stability test and flash calculations are proposed. The performance...

Robust Flash Calculation Algorithm for Microemulsion Phase Behavior

Journal of Surfactants and DetergentsVolume 22, Issue 4 p. 929-930 ERRATUMFree Access Robust Flash Calculation Algorithm for Microemulsion Phase Behavior This article corrects the following: Robust Flash Calculation Algorithm for Microemulsion Phase Behavior Saeid Khorsandi, Russell T. Johns, Volume 19Issue 6Journal of Surfactants and Detergents pages: 1273-1287 First Published online: September 29, 2016 First published: 08 July 2019 https://doi.org/10.1002/jsde.12265AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat In Khorsandi and Johns (2016), certain values in Equations (8), (31) and Figure 2 were published with errors. The correct Equations (8) and (31) are shown below. (8) (31) Figure 2Open in figure viewerPowerPoint Detailed flow chart for new flash calculation algorithm. The gray blocks represent the equations added in this research to complete the model. If data is available, these equations can be further improved, but for our purposes we have selected the simplest possible models. United States provisional patent application 62/379,511 was filed on the new flash calculation algorithm In Figure 2, the second equation in the rightmost box is: In left column, the last entity in the fourth square is “ and are calculated by Eqs. (34)”. The correct Figure 2 is shown on page 2. Finally, the algorithm does not check the consistency of the input parameters. That is, with an improper input the two-phase lobes may overlap. As with any equation-of-state the model must be tuned properly. The ternary phase diagram is helpful to check the consistency of the input parameters. Example ternary diagrams are shown in Figs. 5 to 7 of the article. Reference Khorsandi, S., & Johns, R. T. (2016) Robust flash calculation algorithm for microemulsion phase behavior. J Surfactants Deterg, 19: 1273– 1287. https://doi.org/10.1007/s11743-016-1877-9. Volume22, Issue4July 2019Pages 929-930 FiguresReferencesRelatedInformation

An investigation of the optimum separation conditions in the Degassing stations of one of southern Iraqi oil Field

In field separation facilities operation, operators tend to determine the optimum conditions to maximize revenue.
 The object of this study is to investigate the present number of separation stages and their optimal conditions for degassing stations of oil Field. 
 A computer program model was written to predict the optimal conditions for oil field gas-oil separation stations subject to a given crude oil composition , flow rate and feed temperature and pressure using flash calculations with modified Soave-Redlich-Kwong Equation of state.
 Nine Bottom-hole well samples of reservoir crude oil was collected and subjected to PVT analysis commonly performed on crude oil, Surface stage separators gas samples at steady condition were taken and analyzed by gas chromatography apparatus to determine the gas composition.
 A good agreement was found by comparing theoretical and experimental prediction for gas composition.
 The results indicate that the present five separation stages is the optimum number and the values obtained for these optimum stages pressure are (514.7,119.7,42.7,26.7,14.7 psig) for Summer and (464.7,119.7,42.7,26.7,14.7 Psig) for Winter where the current operation pressures are (614.7,119.7,42.7,26.7,14.7 psi) for Summer and Winter. The total liquid yields in stock tank reaches (1.29, 1.31 %) for summer and winter respectively and the stock tank API Gravity reaches (0.41, 0.42) for summer and winter respectively.

Analyzing separation capacity efficiency of a binary hydrocarbon system (Cyclohexane - N-Pentane) with the help of two distinct methods: Utilizing A Vortex Tube Separator and An Equilibrium Flash Stage (EFS)

The fundamental objective of this preliminary investigation was to simulate the desired separation in a commercially available vortex tube, using a system of hydrocarbons as a surrogate for air. A bench-scale system was constructed, a mixture of 21% cyclohexane and 79% n-pentane was selected, and a parametric study was devised to evaluate the effect of feed conditions on vortex tube separation performance. The desired separation was not achieved using the commercial vortex tube, a unit which was designed for air flow rates much higher than we were using in the bench scale environment. Modifications were made to the equipment in an effort to compensate for the lower flow rates; however, these modifications did not improve attempts to achieve the desired separation. All of the data seem to indicate that the best separations achieved in this study were only equivalent to one equilibrium flash stage. Many of the separations did not even match the equilibrium flash case, which suggests that the action of the commercial vortex tube used in this study produced mixing, entrainment, of other processes which serve to reduce the separation when compared to that of an equilibrium flash.

Element balance formulation in reactive compositional flow and transport with parameterization technique

We present a novel nonlinear formulation for modeling reactive-compositional flow and transport in the presence of complex phase behavior due to a combination of thermodynamic and chemical equilibria in multi-phase systems. We apply this formulation to model precipitation/dissolution of minerals in reactive multiphase flow in subsurface reservoirs. The proposed formulation is based on the consistent element balance reduction of the molar (overall composition) formulation. To predict the complex phase behavior in such systems, we include the chemical equilibrium constraints to the multiphase multicomponent negative flash calculations and solve the thermodynamic phase and chemical phase equilibria simultaneously. In this solution, the phase equilibrium is represented by the partition coefficients, whereas the chemical equilibrium reaction is represented by the activity coefficients model. This provides a generic treatment of chemical and thermodynamic equilibrium within the successive substitution loop of mulmultiphase flash to accommodate chemical equilibrium reactions (precipitation and dissolution reactions). Equilibrium Rate Annihilation matrix allows us to reduce the governing component conservation equations to element conservation equations, while the coupling between chemical and thermodynamic equilibrium is captured by a simultaneous solution of modified multiphase flash equations. The element balance equation written in terms of overall component mole fractions is modified and defined in terms of element mole fractions. Therefore, the primary set of governing equations are the element balance equations and the kinetic equations. This element composition of the mixture serves as an input to the modified multiphase flash computations, whereas the output is fractions of components in each phase, including solids. The nonlinear element–based governing equations are solved with the modified version of the operator-based linearization (OBL) approach where the governing equations are formulated in terms of space- and state-dependent parameters constrained by the solution of the extended multiphase flash. The element balance molar formulation along with the modified multiphase flash has been tested in a simple transport model with dissolution and precipitation reactions. The simulation of multidimensional problems of practical interest has been performed using the adaptive OBL technique. This is the first time when a robust multiphase multicomponent flash based on element fractions is coupled with an element balance–based compositional formulation and tested for multidimensional problems of practical interest. The proposed technique improves both robustness and performance of complex chemical models.

Acceleration of the NVT Flash Calculation for Multicomponent Mixtures Using Deep Neural Network Models

Phase equilibrium calculation, also known as flash calculation, has been extensively applied in petroleum engineering, not only as a standalone application for a separation process but also as an integral component of compositional reservoir simulation. Previous research devoted numerous efforts to improve the accuracy of phase equilibrium calculations, which place more importance on safety than speed. However, the equation-of-state-based flash calculation consumes an enormous amount of computational time in compositional simulation and thus becomes a bottleneck to the broad application of compositional simulators. Therefore, it is of vital importance to accelerate flash calculation without much compromise in accuracy and reliability, turning it into an active research topic in the past two decades. With the rapid development of computational techniques, machine learning brings another wave of technology innovation. As a subfield of machine learning, the deep neural network becomes a promising computation...