Phase Equilibrium Calculations Research Articles

Recrystallization Behavior of Computationally Optimized Low‐Alloy Steel at Various Temperatures and Strain Rates

The dynamic recrystallization (DRX) behavior of SA508‐III steel, a critical material for reactor pressure vessels (RPVs) normally treated by hot forging, is thoroughly examined in this article. In the investigation, elevated temperatures and the coarsening of metallic phases and carbides are revealed to contribute to the degradation of the steel's strength–toughness relationship. Utilizing computational thermodynamics, the stability of secondary phases, including carbides and brittle inclusions, is simulated to enable precise phase equilibrium calculations and accurate prediction of key mechanical properties such as yield strength, tensile strength, and hardness. These simulations facilitated targeted modifications to the alloy composition to enhance the steel's strength and hardenability under high‐temperature, high‐pressure conditions. In this study, alloy composition and processing parameters within the CALculation of PHAse Diagram framework, utilizing the ThermoCalc and JMatPro software packages, are optimized. In the microstructural investigations conducted under various isothermal deformation conditions (1173–1473 K) and strain rates (0.001–1 s−1), it is demonstrated that DRX mechanisms led to varied grain size developments, with a critical strain rate identified at 0.01 s−1 during high‐temperature deformations. In these findings, significant insights are provided into optimizing the mechanical performance of SA508‐III steel for RPV applications.

Phase Behavior of System Carbon Dioxide + Hydrogen Sulfide

The global phase equilibrium behavior of the CO2+H2S system is discussed in this work for temperatures ranging from 160 K up to the critical region. Solid phases of CO2 and H2S and corresponding equilibria have been modeled by considering either a 4th-order equation of state (also used for the fluid phases) or a solid fugacity model for the pure components combined with an activity coefficient model (both coupled with a reference equation of state for the fluid phases).Phase equilibrium calculations have been performed by the minimization of the Gibbs Free Energy of mixing and compared to existing literature data.The types of pressure-mole fraction phase diagrams that can be encountered in the low-temperature thermodynamic region have been described. The temperature and pressure ranges where the phase behavior of the system changes have been identified and a representative phase diagram is presented for each range.

A parallel compositional reservoir simulator for large-scale CO2 geological storage modeling and assessment

Storing CO2 in deep aquifers and depleted gas reservoirs is an effective way to achieve carbon neutrality. However, the numerical simulation of CO2 storage in these formations is challenging due to the complexity of gases-brine systems. The number of gas species included in the gases-brine fluid models of existing simulators cannot meet the rapidly evolving CO2 sequestration scenarios. To address this intricate issue, we developed a three-dimensional fully implicit parallel CO2 geological storage simulator (PRSI-CGCS) on distributed-memory computers based on our in-house parallel platform. This simulator uses a compositional fluid model with a diverse range of gas species, including CO2, C1 ~ C3, N2, H2S, as well as newly added gases H2 and O2, which may be encountered in geological CO2 storages. Besides, we provide more suitable scaling factors for different gases in the stability analysis bypassing (SAB) method to accelerate the gases-brine phase equilibrium calculations. PRSI-CGCS does not incorporate energy conservation equations, and salt precipitation or dissolution is also not considered. Numerical experiments show that our simulator is scalable, robust and validated to simulate large-scale CO2 storage problems with hundreds of millions of grid blocks on a parallel supercomputer cluster. Besides, after our modification on scaling factors, the SAB method can reduce the number of stability analyses by 61.39 % to 88.71 %, thereby reducing simulation time. Furthermore, case studies indicate that injecting O2 and H2 along with CO2 reduces the stability or capacity of CO2 storage and increases the pressure required for injection. However, this impact is not significant when the impurity content is less than 10 %.

A robust and efficient solution for COSMO-based activity coefficient models

COSMO-based activity coefficient models, such as COSMO-RS and COSMO-SAC, offer a powerful tool that bridges quantum chemical calculations with macroscopic phase equilibrium calculations. These models utilize a group contribution methodology similar to UNIFAC but require an expensive numerical solution of the self-consistency equation for interactions among all surface segments, representing a primary bottleneck in their application to analyses that involve extensive phase equilibrium calculations. This work demonstrates that the self-consistency equation can be derived by minimizing the system energy from all pairwise segment interactions. The derivation leads to an optimization-based second-order solution procedure that ensures convergence and enhances efficiency. We demonstrate the robustness and efficiency of the proposed solution using various examples, including a comparison with the classical successive substitution method, and illustrate that COSMO-based models can be coupled with modern second-order convergent algorithms for phase equilibrium calculations. Furthermore, this work reveals the similarity between COSMO-based models and the SAFT method.

Influence of substitution of Cr by Cu on phase equilibria and microstructures in the Fe–Ni–Co–Cr high-entropy alloys

The article describes how substitution of chromium by copper affects phase equilibria in Fe–Ni–Co–Cr high-entropy alloy. The alloys with copper content ranging from 0 to 20 % (at.) of Cu were prepared. The alloys were equilibrated at 900, 800, 700, and 650 °C. The samples were investigated by electron microscopy, EDX spectroscopy, and EBSD method. The face-centred cubic phases have only occurred in equilibrated alloys: austenite matrix, copper-rich FCC(Cu) phase, and regions containing these phases. The compositions of equilibrated samples at annealing temperatures are given. Fine microstructures including a semicoherent FCC phase rich in Cu and an FCC phase including the main magnetic elements (Fe, Co, Ni) were formed. The experimental results were compared with the calculated phase equilibria obtained by the CALPHAD method.

An initial value insensitive constrained linear predictive evolution algorithm for gas–liquid phase equilibrium calculation problems

Heuristic algorithms are gradually becoming a type of new promising methods for solving phase equilibrium calculation problems since they do not have to calculate an initial value in advance like traditional methods such as direct Newton's method and indirect thermodynamic method. A new heuristic optimizer, constrained linear prediction evolution algorithm (CLPE) for phase equilibrium calculation under given volume, temperature, and moles (NVT-flash) is proposed in this paper. CLPE employs the total Helmholtz free energy of the NVT-flash problem as its objective function and employs the volume and moles vector of a certain phase as decision variables. Numerical experiments are conducted on four NVT-flash problems. The consistency between the experimental results and those obtained by some traditional methods verifies that the proposed CLPE is effective. The comparative advantage in computational overhead over the similar algorithms indicates the significance of this study. The success of CLPE can drive more heuristic algorithms to solve NVT-flash problems more efficiently, so as to advance the field of phase equilibrium calculation.

Study of Simulation Method of Porosity and Permeability Parameters of Salt Deposition Reservoir Based on Phase Equilibrium Calculation

Study of Simulation Method of Porosity and Permeability Parameters of Salt Deposition Reservoir Based on Phase Equilibrium Calculation

Investigation of nano-confinement effects on asphaltenic crude oil phase behavior in tight and shale reservoirs: Modeling using CPA-EOS

As a result of strong molecule–molecule and molecule–wall interactions, phase behavior in confined fluids differs significantly from that in bulk fluids. Asphaltene precipitation is a challenging issue for both conventional and unconventional (nano-scale) porous media. In this study, a new model based on cubic-plus-association equation of state (CPA-EOS) was developed for studying phase behavior of asphaltenic crude oil and asphaltene precipitation in nanoporous media. The developed model considers confinement phenomena including shift in the critical properties of components, high capillary pressure, and adsorption/desorption of fluid components on rock surface. For this purpose, necessary modifications were performed on both the EOS and phase equilibria calculations. The developed model was then used to analyze two-phase (vapor–liquid) and three-phase (vapor–liquid–asphaltene) behavior in confined systems. Results demonstrated that confinement phenomena shrink the two-phase envelope and shift the critical point of the mixture. It is also shown that instability of asphaltene in the solution is higher in nanoporous media and increases with reducing pore size. Therefore, the amount of precipitated asphaltene in nanoporous media is higher than that in conventional systems. As adsorption of components with higher molecular weights is more than that of low-molecular weight compounds, the crude oil sample is enriched with lighter components and hence, due to adsorption, bubble point pressure increases, upper branch of dew point curve shifts downward and its lower branch shifts upward, and asphaltene instability increases. Neglecting confinement phenomena results in overestimation or underestimation of saturation pressures as well as asphaltene upper and lower onset points and the proposed model can be of high importance in predicting the extent of asphaltene precipitation during natural depletion or solvent injection in tight oil reservoirs.

A compositional numerical study of vapor–liquid-adsorbed three-phase equilibrium calculation in a hydraulically fractured shale oil reservoir

The development of carbon capture, utilization, and storage technologies has notably advanced CO2-enhanced oil recovery (EOR) in shale oil reservoirs, which are characterized by abundant nanopores. These nanopores induce unique phase behaviors in hydrocarbons, challenging traditional phase equilibrium calculation methods. This paper presents a novel three-phase thermodynamic model (vapor–liquid-adsorbed three-phase equilibrium calculation) that addresses these challenges by considering the nanopore capillary pressure, critical parameter transitions, and material exchange between the adsorbed and bulk phases. Grounded in the multicomponent Langmuir–Freundlich adsorption equation and the Peng Robinson equation of state, this model is integrated into the MATLAB Reservoir Simulation Toolbox using an embedded discrete fracture model framework, enabling detailed study of CO2 and hydrocarbon phase behaviors within shale oil nanopores. The results reveal that there are significant nano-constrained effects on multicomponent fluid phase behavior, particularly in pores smaller than 20 nm, leading to notable changes in bubble and dew point pressures, as well as critical condensation pressures and temperatures. CO2 injection further complicates the system, enhancing interactions and expanding the coexistence region of the liquid and gas phases on the pressure–temperature diagram, especially across varying pore sizes. Optimization research on CO2 huff and puff technical parameters for shale oil reservoirs suggests the following optimal settings: a CO2 injection rate of 100 t/day, a shut-in time of 30 days, and six huff and puff cycles. The results of this study offer critical insights into CO2-EOR mechanisms in shale oil reservoirs and emphasize the importance of nanopore properties in EOR.

A method for calculating two-phase equilibrium: Constrained gray prediction evolutionary algorithm with a surrogate model based on quadratic interpolation

Traditional methods, including direct solution methods based on Newton's method and indirect solution methods based on thermodynamic principles, are the mainstream methods used to solve the volume-temperature flash calculation (called NVT-flash), even though they suffer from drawbacks such as sensitivity to initial value and complexity of derivative calculations. A constrained backtracking search algorithm (CBSA), proposed in 2024, was the first and only metaheuristic algorithm to successfully tackle the NVT-flash problem, which overcomes shortcomings of traditional methods. Considering the advantages of metaheuristic algorithms, a constrained gray prediction evolutionary algorithm with a surrogate model based on quadratic interpolation (CGPE-QI) is proposed in this paper to deal with the NVT-flash problem. CGPE-QI considers total Helmholtz free energy as the objective function, moles vector, and volume of a single phase as variables. Constraints to solve the NVT-flash problem are addressed by using a direct search method and an exterior point method. Numerical experiments on two-phase equilibrium of pure substance and mixtures are carried out employing CGPE-QI. Experimental results are the same as those obtained by traditional methods, which confirms that CGPE-QI can effectively tackle the NVT-flash problem and possesses energy decay property. In particular, the results demonstrate that CGPE-QI is more competitive than CBSA in terms of convergence speed, stability, and calculation cost. CGPE-QI proposed in this paper is the second metaheuristic algorithm to successfully solve the NVT-flash problem, illustrating that metaheuristic algorithms have great potential in solving phase equilibrium calculation problems.

DEVELOPMENT OF AN ALGORITHM FOR CALCULATING COMPONENT COMPOSITION TO IMPROVE THE DEVELOPMENT OF OFFSHORE OIL FIELDS IN THE NORTH CASPIAN BASIN

The paper presents an algorithm to reconstruct the component composition of the mixture based on the results of production modeling in the black oil format and a fixed set of tables with the results of phase equilibrium calculations in a given pressure range. The approach is based on analyzing the ratio of flow rates for each phase and the ratio between average reservoir pressure and saturation pressure. The algorithm takes into account the possibility of oil degassing when saturation pressure decreases, as well as gas breakthrough of gas caps to the bottoms of producing wells.Implementation of the method is based on a unified thermodynamic model of multilayer reservoir, built on the principles of a single set of HC mixture components and uniform parameters of the equation of state on a set of fluid samples for all modeling stages: reservoir model, model of the gathering system and site facilities. In addition to steady-state flow calculations performed together with reservoir modeling, the unified model is planned to be used for dynamic flow calculations in the corresponding simulator (well start/stop), which will allow solving production problems in the process of operation of wells with complex completions.The conversion algorithm is automated using modern high-level tools: Python and data automation components from MS Excel, which eliminates the need for manual data input at all stages and makes it possible to obtain the estimated component composition of produced fluid for any set of wells and for any time step within the forecasting horizon.The obtained compositions are used to verify the reproduction of the main controlled parameters (oil density and gas oil ratio) and can be used for subsequent calculations of fluid transportation and treatment systems.The implemented algorithm has been tested for stability at different ratios of gas and oil flow rates by wells and meets the practical requirements of engineering calculations — the error of oil density is not higher than 2 % and gas factor is not higher than 10 %.

A constrained differential evolution algorithm for calculation of two-phase equilibria at given volume, temperature and moles

A variety of strategies including two types of direct solution methods based on Newton's method and indirect solution methods based on thermodynamic principles have been developed, which can find satisfactory solutions for the phase equilibrium calculation problem at given volume, temperature and moles (NVT-flash). However, these methods are sensitive to the initial values and depend on the objective function's derivative during calculation. To resolve these deficiencies, a constrained differential evolution algorithm (abbreviated as CDE) for calculating two-phase equilibria at given volume, temperature, and moles is presented in this paper. The total Helmholtz free energy is regarded as the objective function, and the moles vector and volume of a certain phase are taken as the decision variables. This paper deals with the constraints of the NVT-flash problem by using direct search method and exterior point method. The results of the investigations on pure substance, binary and ternary mixtures are in agreement with the published data, which proves the effectiveness in solving the NVT-flash problem and the energy attenuation characteristic of the algorithm. The proposed algorithm represents the first successful attempt to apply the meta-heuristic optimization algorithm to solve the phase equilibrium computation under NVT-flash, and it shows the promising application prospect of meta-heuristic optimization algorithms for solving the phase equilibrium calculation problems.

Effects of High Al Content on the Phase Constituents and Thermal Properties in NiCoCrAlY Alloys.

MCrAlY (M = Ni and/or Co) metallic coatings are essential for the protection of hot-end components against thermal and corrosion damage. Increasing the Al content is considered a feasible solution to improve the high-temperature performance of MCrAlY coatings. In this paper, the effects of high Al contents (12-20 wt.%) on the phase constituents and cast microstructures in MCrAlY alloys were studied by high-energy X-ray diffraction and electron microscopy techniques combined with phase equilibria calculations. High Al content improved the stability of β, σ, and α phases. Meanwhile, an evolution of the cast microstructure morphology from a dendrite structure to an equiaxed grain structure was observed. The thermal properties were analyzed, which were closely related to the phase constituents and solid-to-solid phase transitions at evaluated temperatures. This work is instructive for developing high-Al-content MCrAlY coatings for next-generation thermal barrier applications.

Phase behavior of ionic fluid in charged confinement: An associating polymer density functional theory study

AbstractWith the rapid advancement of the new energy industry, porous electrode materials and complex electrolytes have gained widespread usage. Electrolytes exhibit distinctive phase behavior when subjected to the combined influence of confined space and electric fields. However, the measurement and prediction of such phase behavior encounter significant challenges. Consequently, numerous theoretical tools have been employed to establish models for phase equilibrium calculations. Nevertheless, current research in this field has notable limitations and fails to address the confinement of space or complex polymer electrolytes. Considering these shortcomings, an associating polymer density functional theory (PDFT) was developed by modifying excess free energy. This study examines the phase behavior of electrolytes with various chain lengths within diverse confined slits, revealing that the confinement effect and fluid tail chains can narrow the phase diagram. Additionally, a linear correlation between the electric field strength and the phase equilibrium offset has been identified, and a quantitative relationship is derived. The results of this investigation contribute to a deeper comprehension of complex fluid phase behavior and guide the design of electrochemical devices.

Heat sources for Variscan high‐temperature–low‐pressure metamorphism: Petrochronological constraints from the Trois Seigneurs massif, French Pyrenees

AbstractHigh‐temperature–low‐pressure metamorphism is commonly associated with intermediate to felsic magmatism in continental orogenic belts. The heat budgets and transfer mechanisms responsible for such elevated temperatures and partial melting of the upper crust are uncertain. The Trois Seigneurs massif, French Pyrenees, preserves a structurally continuous record of Variscan high‐temperature–low‐pressure metamorphism through a sequence of upper‐to‐mid‐crustal Paleozoic metasedimentary rocks. Conventional thermobarometry and phase equilibria calculations show that metamorphic conditions span ~2.5 kbar, 575°C to suprasolidus conditions of ~6 kbar, 700°C. Peak temperatures depend strongly on depth: temperature gradients of 50–60°C/km are present through the uppermost 12 km of the section; deeper portions (12–20 km) define restricted temperature conditions of ~650–700°C. The lowest‐grade metamorphic rocks preserve the largest spread in monazite 206Pb*/238U dates, from c. 325–285 Ma, while the spread in dates is restricted to c. 305–290 Ma in the highest‐grade rocks. Within this spread, each sample yields a well‐defined population of monazite 206Pb*/238U dates with peaks at c. 305 Ma in the andalusite schists, 295 Ma in the sillimanite schists, and 300 Ma in the migmatite sample. Monazite trace‐element compositions capture a systematic change with decreasing date and increasing metamorphic grade, including a more negative Eu‐anomaly and decreasing Sr concentrations, consistent with co‐crystallizing feldspar; increasing HREE and Y contents, consistent with xenotime breakdown; and decreasing Th/U, reflecting increasing U content during breakdown of inherited zircon. Zircon rims from a granite unit that formed via partial melting of the Paleozoic sedimentary package yields a 206Pb/238U‐207Pb/235U concordia age of 304.1 ± 3.73 Ma. These rims have trace‐element compositions reflecting cogenetic apatite and zircon growth during granite formation. Zircon from a calc‐alkaline granodiorite intrusion preserves a 40 Ma record of melt‐related activity in the lower crust that preceded the regional thermal climax. We interpret these petrochronological data to show that the Trois Seigneurs field gradient including andalusite schist and biotite granite samples represents a genuine geotherm through Variscan orogenic crust during the regional thermal climax at 305 Ma. When combined with constraints from other Pyrenean massifs, the form of the geotherm is consistent with a thermal scenario in which heat is advected to the upper crust by intermediate‐composition magmas generated in the lower crust. A simple thermal model for this process indicates that anatexis in the upper crust may plausibly occur within 10 Ma of the initiation of the lower‐crustal melting. Such a thermal scenario, however, requires focusing of melt through a fertile lower crust and an elevated Moho heat flux. We suggest that this process may have controlled the attainment of high‐temperature–low‐pressure metamorphic conditions along the Variscan belt and may currently be operating in zones of post‐orogenic continental extension.

The role of protolith composition in the formation of tin-enriched granitic melts: A modeling study using the example of the southwest China tin province

Important features of Sn mineralization are the heterogeneous geographic distribution and frequent regional separation from W mineralization in spite some similarities of Sn and W behavior during magmatic processes. Major Sn and W mineralization is often spatially associated with peraluminous granites, which are derived from partial melting of metasediments. Several concepts have been suggested to explain those features, such as a weathering-related Sn-enriched source, Sn redistribution between melts and restite during protolith melting, and extensive fractional crystallization. We demonstrate the importance of protolith composition for the formation of Sn (and W) granites by using a comprehensive bulk-rock composition dataset from Precambrian metasediments of the South China Sn-W province and employing a thermodynamic modeling approach. We used four compositional proxies for phase equilibria calculations, which are the metasediments of the Mengdong, Sibao, Pingbian, and Shuangqiaoshan Groups. It is well documented that those Precambrian metasediments are important protoliths of Sn granites in South China. We present quantitative evaluation of the control of protolith composition in the generation of Sn-enriched granitic melts using South China as example, but our conclusions may also be applicable to worldwide Sn–enriched granites. Our results indicate that the protolith major-element geochemistry controls the anatectic reactions and melt productivity at specific melting conditions, and consequently the partitioning behavior of Sn. Further, pre-enrichment of Sn is crucial to the fertility of granitic melt and may be a prerequisite, particularly for the formation of giant Sn deposits. We propose that the heterogeneous distribution of favorable source rocks is one of the important factors that control the spatial distribution of major Sn (and W) districts in South China and other regions worldwide.

Improvement of augmented free-water flash algorithm based on HV mixing rule and simulated annealing optimization algorithm

The calculation of three-phase equilibrium in CO2-hydrocarbon-water mixtures holds significant importance within numerical simulations, particularly in applications such as CO2-enhanced oil recovery and carbon dioxide sequestration. However, due to the non-ideality of CO2 and the polarity of water, three-phase equilibrium calculations often encounter convergence challenges. The augmented free-water flash algorithm [6], specifically focusing on CO2 dissolution in the aqueous phase, addresses the convergence challenges encountered by traditional three-phase flash algorithms. Despite its accuracy diminishes under conditions of high pressure and high CO2 concentrations, limiting its capability to accurately describe CO2 dissolution in oil-gas-water multiphase systems. The GE (excess Gibbs free energy) type mixing rule can be effectively integrated with equations of state, including PR and SRK, by utilizing activity models like NRTL and UNIFAC, which can be applied to the calculation of thermodynamic parameters for both nonpolar and polar systems and high-pressure complex systems. In this study, based on the augmented free-water assumption, we have developed a new augmented free-water three-phase flash algorithm for CO2/hydrocarbon/water mixtures. This algorithm integrates the PR equation of state with the NRTL activity model, employing the HV mixing rule for CO2-water interactions and the Van der Waals rule for other non-polar components. Furthermore, to enhance computational efficiency, the algorithm incorporates the simulated annealing global optimization algorithm, replacing Newton iteration to more effectively identify the global minima of the complex objective function. The example calculations show that the improved augmented free-water flash algorithm has higher accuracy and efficiency than the traditional augmented free-water flash algorithm. The augmented free-water three-phase flash algorithm proposed in this paper offers a precise model for phase equilibrium calculations essential for numerical simulations in CO2-enhanced oil recovery and carbon dioxide sequestration.

Tectono-metamorphic interaction of upper mantle peridotites and lower crustal units during continental rifting in the western Betic Cordillera

Recent geological mapping conducted in the Ronda Peridotites (Betic Cordillera, S Spain) has revealed a systematic field correlation between lower crustal metamorphic units and different tectono-metamorphic domains of the ultramafic massif. Mylonitic and highly tectonized Spl ± Grt peridotites (i.e., Grt-Spl mylonite and Spl tectonite domains), which are considered to be derived from a thick continental lithosphere, are in contact with garnet-bearing gneisses (i.e., kinzigites) of the Jubrique unit along a narrow but continuous mylonitic shear zone. Phase equilibrium calculations indicate that the metamorphic rocks of the Jubrique unit are consistent with an initial continental setting characterized by normal crustal thicknesses, which underwent two melting events. The first melting occurred at 0.9–1.0 GPa / 770–800 °C and resulted in 13 %melt, while the second one took place at shallower crustal conditions (0.4–0.5 GPa and 710–765 °C) and led to more restricted melt production (2–3 %melt). In contrast, the Spl ± Pl peridotites (Pl-tectonite domain), which are stable only at shallowest mantle levels within a highly extended continental lithosphere, are consistently found exposed in contact with heterogeneous granites and migmatites of the Guadaiza unit. According to new thermodynamic modeling, the Guadaiza metamorphic rocks record a single melting event characterized by a theoretical melt production of 6 to 11 % at the base of a very thin continental crust (ca. 0.3 GPa and 675–710 °C). This process was likely facilitated by influx of external water, necessary to generate high melt fractions observed in the diatexites. The systematic correlation observed between crustal metamorphic units, consistently overlaying the mantle rocks, and specific ultramafic domains of the Ronda massif, suggests that their juxtaposition primarily resulted from the severe extension of the continental lithosphere.U-Pb radiometric dating of zircons from gneisses, migmatites, and heterogeneous granites in the middle crustal rocks of the Guadaiza unit indicates that extensional processes, crustal anatexis, and melt stagnation occurred at around 280 Ma. Comparison of these new radiometric ages with previous results from the Jubrique unit suggests that a Permian high-temperature / low- to medium-pressure event uniformly affected the crustal units over the Ronda Peridotites. This event coincided with the formation of characteristic ultramafic mineral assemblages within the Ronda massif and provides evidence for the interaction between upper mantle rocks and lower- to mid-crustal metamorphic rocks during this period.

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.

Revealing microstructural degradation mechanism induced by interdiffusion between Amdry365 coating and IN792 superalloy

Metallic coatings are widely employed to improve the oxidation resistance of superalloys. However, the interdiffusion between the metallic coatings and the superalloys leads to microstructural degradation in both. Some of the underlying degradation mechanisms are still elusive, e.g., the γ′ (Ni3Al) phase depletion in superalloys, where a large amount of γ′ precipitates are dissolved in the γ matrix even though the incoming Al from coatings indeed increases the Al content. Here, we investigated the interdiffusion behavior between the Amdry365 coating and the IN792 superalloy at 1100 °C, using multiple microscopic techniques and thermodynamics calculations. Our results showed an excellent agreement between experiments and thermodynamics simulations, indicating the dominant role of Al on the initial diffusion-induced phase transitions. We proposed the Al-Cr interference effect to account for the pile-up behavior of Cr and the reduced Al content near the coating/superalloy interface. The local phase equilibrium calculations revealed that the γ′ depletion in the superalloy is primarily attributed to the loss of γ′-forming elements, such as Ta and Ti. Our findings opened up an avenue for studies on the superalloy/coating interdiffusion, contributing to reducing this damaging impact.