Peng-Robinson Equation Research Articles

Adsorption effects on CO2-oil minimum miscibility pressure in tight reservoirs

CO2 miscible injection holds immense potential for enhancing tight oil recovery, where achieving the minimum miscibility pressure (MMP) is pivotal. Adsorption of CO2 and oil in pores affects the CO2-oil MMP in tight reservoirs, necessitating precise nanoscale MMP calculations and understanding influencing factors. Here, we applied a modified Peng-Robinson equation of state (PR-EOS) for nanoscale MMP calculations, incorporating adsorption layers and effective molar volume to describe adsorption effects. Validation against molecular simulations and nanofluidic experiments shows a maximum deviation of 4.6 %. We found that in nanopores, achieving miscibility demands less CO2 than in bulk. The CO2-oil MMP reduces as pore size decreasing, influenced by adsorption, critical point shift and capillarity. At 5 nm, the MMP is 11.12 MPa, 27.8 % lower than the bulk value (15.4 MPa). Adsorption intensifies this reduction by curtailing free molecules and effective pore radius, and becomes more pronounced for lighter hydrocarbon mixtures. However, the nanoscale CO2-oil MMP is equal to the bulk value when rp ≥ 350 nm. Furthermore, a maximum MMP and the corresponding transition temperature exist for each pore size, and increase as pore size increasing. This method provides a valuable tool for optimizing CO2 miscible injection and carbon storage in challenging nanoscale-pore reservoirs.

AP-x,y Equilibrium data of the binary systems of 1-Butanol and 2-Butanol with argon at 313.15 K and 333.15 K – Measurements and modeling

The equilibrium composition of two binary systems (argon–1-butanol and argon–2-butanol) was measured at 313.15 K and 333.15 K and at pressures up to 640 bar. A high-pressure optical view cell was used for the experiments, while theoretical calculations were based on the Peng-Robinson Equation of State with the Boston-Mathias alpha function. Different equilibrium compositions of argon in butanol isomers, as well as butanol isomer in argon were observed despite the similar molecular weight of isomers (M1-butanol = 74.121 g mol−1 and M2-butanol = 74.122 g mol−1) and a functional hydroxyl group. The difference in vapour pressure, dipole moment and solute-solute interactions lead to different solubility values. Nevertheless, the importance of data predicted by theoretical calculations is based on the possibility of obtaining an approximation to the thermodynamic behaviour of the real systems without the necessity of experimental data.

Comparative Evaluation of a Functions and Volume-Translation Strategies to Predict Densities for Gas(es)-Heavy Oil/Bitumen Systems

Summary In this work, a unified, consistent, and efficient framework has been proposed to better predict the density of a gas(es)-heavy oil/bitumen system by using the Peng-Robinson equation of state (PR EOS) and Soave-Redlich-Kwong (SRK) EOS together with α functions and volume-translation (VT) strategies, respectively. With a database comprising 218 experimentally measured densities for gas(es)-heavy oil/bitumen systems, five α functions defined at a reduced temperature (Tr) of 0.70 as well as three new α functions at Tr = 0.60 together with four VT strategies are selected and evaluated. For α Functions 1 to 4 defined at Tr = 0.70, VTs 1 to 4 lead to an overall absolute average relative deviation (AARD) of 7.21%, 9.74%, 7.02%, and 7.16%, respectively, for predicting the mixture densities. For α Function 5 defined at Tr = 0.70, these four VT strategies predict the mixture density with an AARD of 3.13%, 5.01%, 2.92%, and 2.56%, respectively. As for the two new α Functions 7 and 8 defined at Tr = 0.60, these four VT strategies predict the mixture density with an AARD of 1.38%, 2.57%, 1.34%, and 1.67%, respectively, among which VT 3 has a very close prediction compared to an AARD of 1.31% obtained from the ideal mixing rule with effective density (IM-E).

Measurement and Modeling the Properties and Equilibrium of Fluid Systems Involving Carbon Dioxide and Hydrocarbons

On the basis of molecular dynamics modeling (MD modeling) and experimental data pVTx, a study was made of the dynamic and thermodynamic properties of a binary system based on light gases containing heavy oil (A-B). The solvent (A) used was carbon dioxide and n-alkanes (methane, ethane, and propane) in the supercritical fluid (SCF) state. Measurements of the pVTx properties were carried out in the temperature, density, and pressure ranges near the critical parameters of the light gas-heavy oil systems. Based on pVTx data and MD modeling in the A-B system, the diffusion coefficient (D) was determined near the critical parameters of the solvent. The values of D in the binary system SCF carbon dioxide or alkanes containing (methane, ethane and propane) heavy oil from the Siyazan field of Azerbaijan are calculated. The D SCF value of methane and ethane in the A-B system is higher than in a system containing SCF propane at given concentrations (c or x) of heavy oil and temperature. The value of D SCF of light gases in the A-B system increases with an increase in the concentration of heavy oil up to x = 2.5 wt. %. Diffusing molecules of SCF gases reduce the viscosity of heavy oil in the A-B system. Dependence D = f(c) tends to have an asymptotic value with increasing oil concentration. In the A-B system, the dependence of D SCF gases on pressure has a non-monotonic form. To calculate mixtures of light gases, the modified Peng-Robinson equation of state (PR EOS) was used. The isothermal dependence P-x of the carbon dioxide-methane binary system is approximated. The calculated P-x curves are consistent with the experimental ones in the temperature range 277-345 K.

Vapor-liquid equilibrium data and performance analysis on binary mixture of R32 and R1216 for residential air condition system

In order to accurately evaluate the performance of R32 and unsaturated fluorinated olefins (HFOs) binary mixtures in residential air condition (RAC) system, the vapor-liquid phase equilibrium (VLE) data of R32 and R1216 binary mixture has been measured with a liquid phase circulation system in the temperature range from 285 to 315 K. The experimental data were correlated by Peng-Robinson (PR) equation of state with Huron-Vidal (HV) mixing rule and non-random two-liquid (NRTL) activity coefficient model. Maximum deviation of the pressure and the mole fraction was 1.38% and 0.013, respectively. The azeotropic behavior was observed for the R32 and R1216 binary mixture when the mole fraction of R32 was around 0.9. The RAC system with standard refrigeration, heating and variable evaporation temperature operating condition was simulated. The cycle performance of binary mixtures of R32 + R1216, R1234yf and R1234ze(E) at different concentrations was compared. The azeotrope R32/R1216 (molar ratio 0.9/0.1) has an extremely low GWP, the COP, refrigeration/heating capacity per unit volume and condensation pressure close to pure R32, and lower discharge temperature. At the same time, it also has well variable operating conditions performance and can be considered as a drop-in replacement for R32 and R410A in RAC systems.

Predicting the solubility of hydrogen in hydrocarbon fractions: Advanced data-driven machine learning approach and equation of state

BackgroundHydrogen is a free carbon source for energy that attracts massive interest to be utilized during energy transition period in the near future. Molecular hydrogen soon will be a key component in fuels productions. It can be produced through catalytic steam and natural gas. For such processes the accurate estimation of solubility of hydrogen in many alkanes’ solution can have a major impact on the design and optimization of such petrochemical processes. MethodsIn this study, advanced data-driven scheme consisting in a committee machine intelligent system (CMIS) model was proposed for predicting the solubility of hydrogen in many hydrocarbon liquids raging from light n-alkanes C1 to heavy n-alkanes of C46. The CMIS was gained by combining multilayer perceptron (MLP) and cascaded forward neural network (CFNN) beneath a sole model using gene expression programming (GEP). A wide range database of hydrogen solubility in a binary system of hydrogen and various n-alkanes types was considered for developing the intelligent model. Besides, the reliability of the physics-based models, namely the Peng–Robinson equations of state (PR EOS) was checked for predicting the solubility of H2 in n-alkanes. Significant findingsThe main results demonstrated that the developed CMIS scheme can estimate the solubility of hydrogen in n-alkanes with a quite low computational cost and excellent performance, where the yielded overall RMSE and R2 values were 0.0033 and 0.9972, respectively. Besides, the established machine learning based model is capable of providing a good match against a wide range of experiment data. Furthermore, it is found that the implemented CMIS paradigm is superior to the existing intelligent and physics-based models in terms of accuracy. Lastly, the result of this work is vital for increasing the accuracy of hydrogen solubility in various hydrocarbon solvents required for process optimization of the hydrogen production units.

Modelling a CO2 meter for a petroleum multiphase mixture at subsea conditions

Measuring high levels of carbon dioxide (CO2) in Brazilian pre-salt production flows remains a considerable technological challenge. The complexity of the three-phase flow and the variable CO2 solubility within each phase poses difficulties in accurately measuring CO2 in this scenario. Moreover, existing CO2 measurement techniques designed for single-phase fluids prove insufficient under mixed-phase conditions. This study proposes a methodology for a simple CO2 meter capable of determining the CO2 content in an oil and gas production stream. The proposed meter operates by analyzing the pressure change during a heating assay of an imprisoned sample. A computational model was developed in the ASPEN HYSYS® process simulator with the Peng-Robinson Equation of State to calculate the mixture properties emulating the isochoric process in the meter under different CO2 levels and initial conditions. The modelling results indicate that the pressure-temperature (P-T) behavior exhibits linearity with a slope that increases with higher CO2 content, which is characteristic of many pre-salt production fields. The model successfully reproduced published experimental data for an isochoric process.

Simulation study of hydrogen sulfide removal in underground gas storage converted from the multilayered sour gas field

A simulation study was carried out to investigate the temporal evolution of H2S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H2S (27.2 g/m3), and the lower layer Jia-1 contains a low concentration of H2S (14.0 mg/m3). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H2S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H2S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H2S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H2S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H2S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H2S removal. After nine cycles, the produced gas’s H2S concentration can be lowered to 20 mg/m3. Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H2S concentration of the produced gas to 20 mg/m3, thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H2S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.

Thermodynamic Properties of 1-Butanol + Ethyl Laurate Binary Mixtures by Combining Experimental Speeds of Sound with Volume Translated Peng–Robinson Equation of State

Thermodynamic Properties of 1-Butanol + Ethyl Laurate Binary Mixtures by Combining Experimental Speeds of Sound with Volume Translated Peng–Robinson Equation of State

Numerical study of the transient behaviors of vapour-liquid equilibrium state CO2 decompression

The vapor–liquid equilibrium (VLE) state of CO2 commonly appears in pipelines for its transport, refrigeration systems, and large-scale trans-critical cycle systems. However, the behavior of sudden leaks in such systems remains unclear, which poses a challenge in assessing the risk of leakage. This work is focused on the decompression behavior of VLE state CO2 with different volume fractions of vapor phases in high-pressure pipeline leakage, specifically with the development of a computational fluid dynamics (CFD) model with a nonequilibrium phase transition and the real gas model. The results suggest that the Peng-Robinson Equation of State (PR EoS) is more conservative in predicting the degree of superheat than that of Span-Wagner (S-W) EoS and GERG-2008 EoS. Moreover, it is found that the initial volume fraction of the vapor phase in VLE state CO2 plays a crucial role in determining the characteristics of sudden leakage, such as pressure, temperature, and decompression wave speed both inside and outside the pipe. However, the position of the Mach disk remains unaffected by the initial volume fraction of the vapor phase. The initial vapor volume fraction of 0.2 has the most significant impact on the transient behaviors of the leakage, that is, the speed of the initial decompression wave is approximately 1.46 times slower than that of pure liquid CO2, the pressure and temperature start to decrease approximately 0.46 ms after those of pure liquid CO2, which is about 5.1 times later. Additionally, the peak pressure of the near-field jet is 6.3% higher and the maximum velocity is 11.4% higher than that of pure liquid CO2. It hopes that this work will contribute to the improvement of research models that assess the consequences of potential high-pressure pipeline rupture scenarios.

Assessment of the pseudopotential lattice-Boltzmann method for modeling multiphase fuel droplets

An improved pseudopotential lattice–Boltzmann model was proposed for simulating multiphase flow dynamics to describe fuel droplets, and its thermodynamic consistency was tested against the Peng–Robinson equation of state. The studied liquid fuels included paraffinic hydrocarbons with a different number of carbon atoms (C[Formula: see text]–C[Formula: see text]), methanol (CH[Formula: see text]OH), hydrogen (H[Formula: see text]), ammonia (NH[Formula: see text]), and water (H[Formula: see text]O). To improve accuracy and reduce the magnitude of the spurious currents, the multi-relaxation times collision operator was implemented and the forcing term was computed using the hybrid pseudopotential interaction force with an eighth-order isotropic degree. The pseudopotential lattice–Boltzmann model accurately predicted the equilibrium densities and captured satisfactorily the thermodynamic vapor-liquid coexistence curve given by the analytical solution of the Peng–Robinson equation of state for acentric factors ranging from [Formula: see text]0.22 to 0.56, keeping the maximum average error for the liquid and vapor branches below 0.8% and 3.7%, respectively. Nevertheless, Peng–Robinson was found to be insufficiently accurate to replicate the actual thermodynamic state, especially for H[Formula: see text]O and CH[Formula: see text]OH, for which the results strongly deviated from the experimental vapor-liquid equilibrium densities and reached average errors for the vapor phase of nearly 28%. Furthermore, the surface tension ([Formula: see text]) was retrieved using the multiphase pseudopotential lattice–Boltzmann results and served to verify the thermodynamic consistency of the pseudopotential lattice–Boltzmann with respect to the parachor model. Lastly, the pseudopotential lattice–Boltzmann model was also shown to predict accurately the transient behavior of oscillating droplets. Overall, the enhanced model satisfactorily predicted the properties and behavior of the substances for a wide range of conditions.

Scalable simulation of coupled adsorption and transport of methane in confined complex porous media with density preconditioning

The growing significance of shales and tight formations in the transition to less carbon-intensive and clean energy drives the research endeavor to understand the physics of gas flow within these systems. However, shales are composed of massively heterogeneous physical and chemical features. Most nano-sized pores connect to millimeter-scale fractures, leading to multiscale transport. These nano-scale pore throats demonstrate non-classical flow behavior, such as non-negligible slip velocities and adsorbed gas layers at the boundary. As a result, classical computational fluid dynamics models do not capture the physics. In this work, we develop a coupling scheme for the multiple-relaxation-time (MRT) lattice Boltzmann (LB) method that integrates the Peng-Robinson equation of state into a pseudo-potential interaction model to capture the physics of methane flow in irregular networks of channels that represent nano-scale porous media. We use atomistic simulations to calibrate and validate our model in slit nano-channels. We propose a preconditioning scheme to initialize the coupled transport and adsorption simulation of methane in complex porous media. The results of this implementation of LB agree with Direct Simulation Monte Carlo (DSMC) and Molecular Dynamics (MD) simulations. We then scale up the LB implementation through vectorization and indirect addressing. We parallelize it using Message Passing Interface (MPI) and OpenMP frameworks to simulate transport and adsorption in complex media with a million lattices. We analyze the differences between coupled and transport-only simulations in two case studies and show that considering phase behavior, i.e., adsorption, can significantly change the flow behavior. This work constitutes an important step towards bridging the gap between molecular flow and system-scale behavior of complex disordered porous media.

Cryogenic CO2 capture from oxy-combustion flue gas by a hybrid distillation + physical absorption process

Hybrid flowsheets are defined, in the context of process intensification, as alternatives suitable for replacing energy-intensive separation methods through the combination of more than one unit operation. Given the undoubted importance of carbon capture, utilization, and storage (CCUS) in the next decades in the path to net-zero emissions and even negative emissions scenarios, this work focuses on CO2 capture from an oxy-combustion flue gas by means of a distillation-based hybrid process that avoids CO2 freeze-out, which is capable of delivering a liquid CO2-rich stream that can in principle be pumped to transport pressures with lower energy consumption in comparison to conventional post-combustion CO2 capture processes based on chemical absorption. A distillation-based process and a hybrid distillation + physical absorption process have been studied based on simulations in Aspen Hysys® V11 using the Peng-Robinson Equation of State and the “Acid Gas – Physical Solvents” thermodynamic property package. Firstly, a CO2 capture process based on cryogenic distillation has been proposed and a sensitivity analysis on the operating pressure and specified CO2 recovery has been performed in order to determine the most convenient configuration, balancing capital and operating costs. Then, a hybrid capture process has been proposed and analyzed, where cryogenic distillation is the bulk removal step and physical absorption into a mixture of homologues of the dimethylether of polyethylene glycol (DEPG) is the finishing step. Energy and economic analyses have shown that the hybrid process, delivering a CO2 product respecting the stringent purity requirement on the oxygen content for application for Enhanced Oil Recovery (EOR) and in the food industry is less energy intensive than the standalone cryogenic distillation, though it is characterized by higher capital costs.

Measurement and thermodynamic modeling of solubility of Erlotinib hydrochloride, as an anti-cancer drug, in supercritical carbon dioxide

Low water solubility is the major problem in the formulation and development of new chemical compounds as well as their generic development. The solubility of anti-cancer drug, Erlotinib hydrochloride, in supercritical carbon dioxide was investigated for the first time at various temperatures and pressures (308-338 K and 12-30 MPa). Based on the results, the solubility of Erlotinib HCL varied in the range of 1.20 × 10−6-2.12 × 10−5 g/l. The correlation of solubility data was studied with Peng-Robinson's equation of state and four density-based semi-empirical models including Chrastil, Bartle et al., Méndez-Santiago, Teja, Kumar-Johnston, and modified Wilson model. The accuracy of models was also explored based on statistical criteria, including average absolute relative deviation (AARD %) and adjusted correlation coefficient (Radj). The modified Wilson model exhibited superior correlation with empirical solubility data in supercritical carbon dioxide (AARD=10.45 %, Radj=0.9876).

Phase equilibrium determination of the binary system globalide + pressured propane: Experiments and thermodynamic modeling

Globalide is a macrolactone used recently as a monomer in polymerization processes in several kinds of research due to its ability to produce biodegradable and biocompatible polyesters suitable for applications in biodegradable packaging and biomedical devices. Polymerization processes traditionally use organic solvents and metallic/chemical catalysts that may leave toxic residues in the final polymer. To obtain polymers free of organic solvents, the use of pressurized gases as green solvents has been investigated. In this context, knowing the phase behavior of these systems is essential to understand the proper conditions of the polymerization process, ensuring that the reaction occurs in single-phase conditions. This work reports phase equilibrium studies of Gl + propane systems at temperatures of 313.15, 323.15, 333.15, and 343.15 K, and propane mass fractions between 0.1 and 0.9001. All observed phase transitions occur in pressures lower than 2.5 MPa, indicating that propane is a solvent that requires less energy expenditure than systems with CO2, being an economic advantage in the polymerization process. Peng-Robinson equation of state with a constant binary interaction parameter adjusted adjustment to the experimental data well.

Thermodynamic study for the (butyl, hexyl and octyl) acetoacetate under high pressure CO2

Understanding the phase behavior of binary liquid mixtures containing butyl acetoacetate, hexyl acetoacetate, and octyl acetoacetate under high-pressure supercritical CO2 (sc-CO2) is essential for several applications. The solubility curves for these binary mixtures have been investigated at different temperature and pressure ranges, specifically between 313.2 K and 393.2 K and 2.39 MPa to 23.83 MPa. The three systems, namely butyl acetoacetate, hexyl acetoacetate, and octyl acetoacetate in high-pressure sc-CO2, exhibit critical mixture curves and a maximum in pressure–temperature (P, T) diagrams between the critical point of butyl acetoacetate/hexyl acetoacetate/octyl acetoacetate and carbon dioxide. These characteristics of the critical mixture plot fall under the category of type-I behavior.The Peng-Robinson equation, which utilizes van der Waals mixing rules and two interaction parameters, is employed to correlate experimental solubility curves and critical mixture curves of the aforementioned three systems. The root mean square deviation percentage (RMSD%) is calculated at each temperature (using temperature-dependent adjusted parameters) for the butyl acetoacetate + sc-CO2, hexyl acetoacetate + sc-CO2, and octyl acetoacetate + sc-CO2 systems, and it ranges from 3.11% to 5.92%, 2.09% to 3.97%, and 1.70% to 3.02%, respectively.

Investigation of the Properties of Hydrocarbon Natural Gases Under Confinement in Tight Reservoirs Due to Critical Properties Shift

Pure components exhibit different phase behavior and critical properties shift when confined, primarily due to increased molecules-pore wall interactions. While extensive research has focused on modeling this behavior for pure components, there is a need to extend these models to hydrocarbon gas mixtures in tight and shale reservoirs to understand the deviation of gas properties from bulk behavior. The study utilizes the Peng–Robinson equation of state to calculate gas properties, considering the shift in critical properties of pure components due to confinement in EOS parameter calculations. Trend analysis investigates the effect of pore size reduction on gas properties, introducing the concepts of the confinement impact factor and specific pore radius. Correlation analysis explores the relationships between variables. Nonlinear regression analysis leads to the development of a new correlation that accounts for confinement effects on gas properties. The findings reveal that the deviation from bulk properties depends on the pore radius, pressure, temperature, and gas composition. The magnitude of deviation ranges from negligible to exceeding 15% under specific conditions of high pressure, low temperature, small pore radius, and rich gas composition. Gas viscosity experiences the most significant alteration, followed by density, while the gas compressibility factor also displays a noticeable impact. The isothermal gas compressibility coefficient demonstrates minimal to no response to confinement. Decreasing pore radius increases the gas compressibility factor, while gas viscosity and density decrease. The obtained results are crucial for shale and tight reservoir engineering calculations, particularly in adjusting gas properties in reservoir simulation and production modeling software.

Phase behaviour and physical properties of dimethyl ether (DME)/flue gas/water/heavy oil systems under reservoir conditions

The application of a mixture of dimethyl ether (DME) and flue gas (i.e., CO2 + N2) is a promising method to recover heavy oil; however, the phase behaviour and physical properties of DME/flue gas/water/heavy oil systems are not well quantified. In this study, theoretical and experimental techniques are developed to determine phase behaviour and physical properties of the aforementioned systems at pressures ranging from 2 MPa to 20 MPa and temperatures spanning from 352.15 K to 433.15 K. Experimentally, eight constant composition expansion (CCE) tests are carried out to obtain new experimental data for the DME/flue gas/water/heavy oil systems for the first time. Theoretically, a thermodynamic model that incorporates the Peng-Robinson equation of state (PR EOS), a modified α function, the Péneloux volume-translation strategy, and the Huron-Vidal (HV) mixing rule has been modified to reproduce the measured phase equilibria data. The tuned binary interaction parameters (BIPs) are utilized in conjunction with the thermodynamic model to accurately predict saturation pressure (Psat) and swelling factors (SFs) with a root-mean-squared relative error (RMSRE) of 3.32% and 0.57%, respectively. Furthermore, the newly proposed model demonstrates its high accuracy in forecasting the oleic/vapor (LV) two-phase boundaries for N2/heavy oil systems and DME/CO2/heavy oil systems with an RMSRE of 1.93% and 2.77%, respectively. Similarly, the accuracies of the predicted aqueous/oleic/vapor (ALV) three-phase boundaries for N2/water/heavy oil systems and DME/flue gas/water/heavy oil systems are 2.85% and 3.47%, respectively. Water is found to increase the phase boundaries for DME/CO2/heavy oil systems but decrease those of N2/heavy oil systems and DME/flue gas/heavy oil systems. Additionally, as the concentration of N2 and/or CO2 in the mixture is increased, its Psat is increased.

Phase behavior and hydrocarbons distribution in shale oil during EOR with nano-confinement effect

The pore structure of shale reservoirs leads to the complex phase behavior of shale reservoir fluids, which is aggravated due to changes in fluid composition during reservoir development. Effective prediction of changes in the phase behavior of fluids in shale reservoirs is important. This paper proposes a pore-size-dependent Peng-Robinson equation of state (PR-EOS) to describe phase behavior in nanopores. The approach considers the shift of critical parameters and the gas-liquid capillary pressure and compiles by MATLAB. The verification of the model is satisfying by matching the result with Tnavigator PVTi using the published date. The results show that fluids in nanoscale pores are more likely to exhibit near-critical or condensate states. We also compare the changes in phase behavior when fluids dissolve CO2 and CH4 and observe the phase transition (from gaseous to liquid phase) of the lighter crude oil sample that dissolved more gas during the differential liberation experiment (DL). Finally, we use CO2 pre-pad energized fracturing of a shale oil reservoir in northern China as an example to explain abnormal production performances, such as a majority of light hydrocarbons in the produced fluid of the well during the flow back stage, single gas phase production in the early production stage, and stable gas/oil ratio (GOR) in the process of development. Our novel methodology and phase behavior change mechanism can enhance our understanding of the phase behavior of fluids in shale oil reservoirs during enhanced oil recovery.

Solubility of buprenorphine hydrochloride in supercritical carbon dioxide: Study on experimental measuring and thermodynamic modeling

Nowadays, supercritical fluids (SCFs) technologies present a processing option for obtaining new products with noteworthy characteristics. Access to reliable solubility data of pharmaceutical compounds in SCFs is considered as the first step for recrystallizing, separating, and producing nano particles via processes based on this type of technique. In this study, high-pressure solubility of buprenorphine hydrochloride, a strong pain reliever, in supercritical carbon dioxide (scCO2) was measured at temperature and pressure conditions of 308–338 K and 120–270 bar, for the first time. The minimum and maximum solubility values, in terms of equilibrium mole fractions, were found to be 0.131 × 10-4 (at 338 K and 120 bar) and 4.752 × 10-4 (at 338 K and 270 bar), respectively. Thereafter, the obtained data were correlated using two different approaches, namely Peng-Robinson (PR) equation of state (EoS) and a set of semi-empirical models. Results from applying statistical criteria indicated that Jouyban and Sodeifian models are suitable choices for predicting solubility data. Furthermore, using the obtained correlation results, the total and vaporization enthalpies of buprenorphine hydrochloride dissolution in scCO2 were estimated to be 65.59 and 85.60 kJ/mole, respectively.