Effects of compositional variations on CO2 foam under miscible conditions

Foam can mitigate the associated problems with the gas injection by reducing the mobility of the injected gas. The presence of an immiscible oleic phase can adversely affect the foam stability. Nevertheless, under miscible conditions gas and oil mix in different proportions forming a phase with a varying composition at the proximity of the displacement front. Therefore, it is important to understand how the compositional variations of the front affect the foam behavior. In this study through several core‐flood experiments under miscible condition, three different regimes were identified based on the effects of the mixed‐phase composition on CO₂ foam‐flow behavior: In Regime 1 the apparent viscosity of the in‐situ fluid was the highest and increased with increasing x_CO2. In Regime 2 the apparent viscosity increased with decreasing x_CO2. In Regime 3 the apparent viscosity of the fluid remained relatively low and insensitive to the value of x_CO2. © 2017 American Institute of Chemical Engineers AIChE J, 64: 758–764, 2018     

Prediction of CO2-Oil Minimum Miscibility Pressure Using Soft Computing Methods

Searching for computational approaches for determination of the minimum miscibility pressure (MMP) is highly requested during the miscible gas injection process. New models, namely, the stochastic gradient boosting (SGB) algorithm and two distinct hybrid artificial neural network (ANN) models were used to predict CO₂ MMP as a function of reservoir temperature, mole percent of volatile oil components, mole percent of intermediate oil components, molecular weight of pentane-plus fraction in the oil phase, mole percentage of CO₂ in injected gas, volatile components, and intermediate components in the injected gas based on 144 published data points. The SGB model was found to provide the better performance. The reservoir temperature turned out to be the most important factor.     

Effect of operating pressure, matrix permeability and connate water saturation on performance of CO2 huff-and-puff process in matrix-fracture experimental model

The main objective of study is to examine the performance and efficiency of CO₂ huff-and-puff process for improving oil recovery and subsequent storage of CO₂ in light-oil fractured porous media through designing and conducting targeted experiments.The experimental set-up consisted of a high-pressure stainless steel cell made specially to hold a cylindrical core with spacing around it, simulating a matrix and its surrounding fracture environment. The matrix was saturated with normal decane, which was used as oil during the experiments. A total of six separate sets of huff-and-puff experiments, using CO₂ as solvent, were conducted under operating pressures of 250, 500, 750, 1000, 1250, and 1500 psi. The temperature was kept constant (35 °C) during all tests. Each set of the huff-and-puff experiments was conducted by injecting CO₂ in the fracture system surrounding the core (injection step). Then, the system was shut-in for a period of 24 h to allow CO₂ to diffuse from fracture into the oil in matrix (soaking period step). At the end of the soaking period, the pressure was released and the oil production was measured (production step). The above cycle was repeated until no more oil was produced.The results obtained show that when CO₂ was injected at 1500 psi through a huff-and-puff process, it recovers more than 95% of oil from a fracture-matrix experimental model saturated with normal decane. Also indicates that at such a pressure, 45% of initial oil-in-place can be recovered during the first cycle. However, when CO₂ was injected at pressures below CO₂-nC₁₀ minimum miscibility pressure (MMP), the maximum recovery factor achieved was less than 50%. Similarly, recovery factor of the first cycles performed at pressures below MMP were much lower (less than 30%) compare to those conducted at miscible condition. This indicates that miscible huff-and-puff process is a viable option for fractured porous media.As part of this study, effects of matrix permeability, and connate water saturation on the performance of huff-and-puff process in fracture-matrix core set-up at both immiscible and miscible conditions were studied. Results indicate that presence of connate water saturation is beneficial to immiscible CO₂ huff-and-puff process while it has almost negligible effect on the performance of this process when performed at miscible conditions. In presence of connate water saturation more than 70% of oil-in-place was recovered at immiscible condition compare to a maximum of 45% recovered when matrix was 100% saturated with normal decane. Results of the tests performed in a core with permeability about 10 times higher than the original core shows similar production trends. However, recovery factor in the high permeable core was slightly less than twice of that in low permeable core at immiscible condition. According to this study, effect of core permeability was less pronounced when CO₂ was injected at miscible conditions.     

Geochemical modeling and experimental evaluation of high-pH floods: Impact of Water–Rock interactions in sandstone

Injection of alkaline solutions in reservoir leads to mineral dissolution and precipitation, possibly resulting in changes in permeability and porosity, and consequently altering solution pH. Accurate prediction of pH, alkali consumption and aqueous chemistry changes are required to design suitable chemical blends in alkaline-polymer (AP) or alkaline-surfactant-polymer (ASP) flooding. Excessive consumption of alkali can result in degradation of flood performance and lower than expected oil recovery. We report state-of-the-art geochemical simulation results for sandstone reservoir mineral assemblages and alkali solutions (NaOH, Na₂CO₃, and NaBO₂) employed in AP and ASP formulations. Single-phase high-pH corefloods were completed using Berea sandstone and reservoir samples to calibrate and validate geochemical simulations. Results show that rock-fluid interactions depend strongly on mineral type and amount, alkaline solution injection flowrate, and composition of the injected and formation water. Anhydrite, a commonly found calcium sulfate, significantly impacts pH buffering capacity, water chemistry and permeability damage against conventional alkali agents in chemical flooding particularly for Na₂CO₃, but no significant pH buffering is observed during NaBO₂ flooding. Experimental data and model results show that the pH-buffering effect is maintained even after several pore volumes of alkaline solution are injected, if a sufficient fraction of relevant minerals is present. The end consequence of this is insufficient alkalinity for reactions with the oil phase and the likely formation damage.     

Simulation modeling of the phase behavior of palm oil-supercritical carbon dioxide

The phase behavior of crude palm oil (CPO) with supercritical CO₂ was successfully modeled in an Aspen Plus^® 10.2.1 commercial simulator (Aspen Technology Inc., Cambridge, MA) using the Redlich-Kwong-Aspen (RKA) equation of state thermodynamic model. The modeling procedure involved estimating pure component vapor pressures and critical properties and computing a regression of phase equilibrium behavior. The interaction parameters for the RKA model were obtained from the regression of experimental phase equilibrium data for a binary system of palm oil components-supercritical CO₂ available in the literature. The distribution coefficients and solubilities of palm oil components obtained from this simulation showed good agreement with experimental data obtained from the literature. The model provides an efficient and cost-effective alternative for the preliminary design and optimization of a supercritical fluid extraction process involving a complex CPO-supercritical CO₂ system.     

Carbon dioxide flooding for enhanced oil recovery: Promise and problems

Of the enhanced oil recovery methods currently being considered for application to many of the nation’s older oil fields, carbon dioxide flooding may offer the largest potential for additional oil recovery. The physical mechanisms by which CO₂ contacts and mobilizes crude oil are reviewed. Influence on the displacement process of factors such as the phase behavior of CO₂-crude oil mixtures, swelling of oil by dissolved CO₂, and reduction of oil viscosity are considered. Adverse effects of the viscous instability which occurs when very low viscosity CO₂ displaces the more viscous oil and water are dicussed. Advantages and disadvantages of three potential methods for controlling the mobility of CO₂ are reviewed: thickening CO₂ with polymeric additives, reduction of CO₂ mobility by high water saturations, and use of surfactants to generate foam-like emulsions of water and CO₂. Field experience to date and the recent surge in field activity are discussed. Finally, a brief assessment of the future of CO₂ flooding research and practice is offered.     

Experimental Study of In-Situ CO<Subscript>2</Subscript> Foam Technique and Application in Yangsanmu Oilfield

The Yangsanmu oilfield of Dagang is a typical heavy oil reservoir. After the maximum primary production (waterflooding), more than half of the original oil is still retained in the formation. Therefore, the implementation of an enhanced oil recovery (EOR) process to further raise the production scheme is inevitable. In this work, a novel in-situ CO₂ foam technique which can be used as a potential EOR technique in this oilfield was studied. A screening of gas producers, foam stabilizers and foaming agents was followed by the study of the properties of the in-situ CO₂ foam systems through static experiments. Core-flooding experiments and field application were also conducted to evaluate the feasibility of this technique. The results indicated that the in-situ CO₂ foam system can improve both the sweep and displacement efficiencies, due to the capacity of this system in reducing oil viscosity and interfacial tension, respectively. The EOR performance of the in-situ CO₂ foam system is better than the single-agent and even binary system (surfactant-polymer) flooding. The filed data demonstrated that the in-situ CO₂ technique can significantly promote oil production and control water cuts. These results are believed to be beneficial in making EOR strategies for similar reservoirs.     

Effect of CO<Subscript>2</Subscript> concentration on the performance of different thermodynamic models for prediction of CH<Subscript>4</Subscript>+CO<Subscript>2</Subscript>+H<Subscript>2</Subscript>O hydrate equilibrium conditions

Accurate prediction of phase equilibria regarding CH₄ replacement in hydrate phase with high pressure CO₂ is an important issue in modern reservoir engineering. In this work we investigate the possibility of establishing a thermodynamic framework for predicting the hydrate equilibrium conditions for evaluation of CO₂ injection scenarios. Different combinations of equations of state and mixing rules are applied and the most accurate thermodynamic models at different CO₂ concentration ranges are proposed.     

Modelling carbon dioxide solubility in ionic liquids

Solubility information for CO₂ in different ionic liquids, ILs, in part can potentially be used to select a specific IL for the separation of CO₂ from hydrocarbon fluids. Unfortunately, not all CO₂–IL systems have been experimentally described at similar temperatures and pressures; therefore, a direct comparison of performance by process simulation is not always possible. In the extreme cases, the design of a CO₂ separation process may require predicting the CO₂–IL equilibria for which there are no available solubility data. To address the need for this information, a semi‐empirical correlation was developed to estimate the dissolution of CO₂ in CO₂–IL solvent systems. The theoretical COSMO–RS calculation method was used to calculate the chemical potential of CO₂ in a wide variety of ILs and the Soave–Redlich–Kwong equation was used to calculate the fugacity coefficient of the CO₂ vapour phase. The model was correlated with available literature data, yielding an average error of AAR = 23% and small bias. © 2012 Canadian Society for Chemical Engineering     

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors

On investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO₂ miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO₂. Both isocyanates and polyols are CO₂-miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO₂. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO₂-soluble compounds may have a com̀patibilizing effect on less CO₂-soluble materials.     

Sorption and transport of CO2 in PVF2/PMMA Blends

The sorption and transport of CO₂ in miscible PVF₂/PMMA blends are reported at 35°C as a function of pressure from 1 to 25 atm. Significant plasticization by CO₂ is evident for all blend compositions. This effect induced further crystallization of PVF₂ for some blends, altered the shape of sorption isotherms for blends with a glassy amorphous phase, and resulted in permeabilities which increased with pressure for all compositions. Modified sorption and transport models to account for plasticization are used to analyze the data. The effect of crystallinity on observed behavior has been accounted for using approximate models to allow comparison of responses of sorption and transport with blend composition.     

Experimental studies and discrete thermodynamic modeling on supercritical CO2 extractions of a hexadecane and crude oil

Continuous multiple-contact experiments using a supercritical CO₂ were performed to study the phase equilibrium behavior of the dynamic extractions of a hexadecane and crude oil. The extraction yields increased as CO₂ density increased with a pressure rise at constant temperature. The rates of extractions were also greater at higher pressure. The simulated distillation analysis of extracted crude oil samples represented that the earlier extracts contained lighter compounds and the latter extracts contained progressively heavier compounds. These compositional changes occurring during a dynamic extraction were also ascertained by phase-equilibrium flash calculations using the equations of state and a pseudo-component lumping method. Two different equations of state, Soave-Redlich-Kwong and Peng-Robinson, were used to predict the equilibrium compositions of the extract phase that is a supercritical carbonic phase. The results of phase behavior calculations established the nature of the extraction and partitioning process as a function of time. These results also provided reasonable agreement between the experimental data and the calculated values.     

Dynamic modeling of CO2 absorption from coal-fired power plants into an aqueous monoethanolamine solution

Among carbon capture and storage (CCS), the post-combustion capture of carbon dioxide (CO₂) by means of chemical absorption is actually the most developed process. Steady state process simulation turned out as a powerful tool for the design of such CO₂ scrubbers. Besides steady state modeling, transient process simulations deliver valuable information on the dynamic behavior of the system. Dynamic interactions of the power plant with the CO₂ separation plant can be described by such models. Within this work a dynamic process simulation model of the absorption unit of a CO₂ separation plant was developed. For describing the chemical absorption of CO₂ into an aqueous monoethanolamine solution a rate based approach was used. All models were developed within the Aspen Custom Modeler^® simulation environment. Thermo physical properties as well as transport properties were taken from the electrolyte non-random-two-liquid model provided by the Aspen Properties^® database. Within this work two simulation cases are presented. In a first simulation the inlet temperature of the flue gas and the lean solvent into the absorber column was changed. The results were validated by using experimental data from the CO₂SEPPL test rig located at the Dürnrohr power station. In a second simulation the flue gas flow to the separation plant was increased. Due to the unavailability of experimental data a validation of the results from the second simulation could not be achieved.     

A comparative study of carbon dioxide capture capabilities between methanol solvent and aqueous monoethanol amine solution

Simulations have been performed to compare the performance of CO₂ capture power between 98.5 wt% methanol solvent and 30 wt% MEA aqueous solution. A general purpose chemical process simulator, PRO/II with PROVISION release 8.3 was used for the modeling of CO₂ capture process. For the simulation of CO₂ capture process using methanol as a solvent, NRTL liquid activity coefficient model was used for the estimation of the liquid phase non-idealities, Peng-Robinson equation of state model was selected for the prediction of vapor phase non-idealities, and Henry’s law option was chosen for the prediction of the solubilities of light gases in methanol and water solvents. Amine special thermodynamic package built-in PRO/II with PROVISION release 8.3 was used for the modeling of CO₂ capture process using MEA aqueous solution. We could conclude that the 30 wt% of MEA aqueous solution showed better performance than the 98.5 wt% methanol solvent in CO₂ capture capability. Through this study, we tried to compare the differences between the two processes from the aspects of capital and operating costs using a commercial process simulator. This will guide the optimal process design in the carbon dioxide capture process.     

One‐dimensional productivity assessment for on‐field methane hydrate production using CO2/N2 mixture gas

The direct recovery of methane from gas hydrate‐bearing sediments is demonstrated, where a gaseous mixture of CO₂ + N₂ is used to trigger a replacement reaction in complex phase surroundings. A one‐dimensional high‐pressure reactor (8 m) was designed to test the actual aspects of the replacement reaction occurring in natural gas hydrate (NGH) reservoir conditions. NGH can be converted into CO₂ hydrate by a “replacement mechanism,” which serves double duty as a means of both sustainable energy source extraction and greenhouse gas sequestration. The replacement efficiency controlling totally recovered CH₄ amount is inversely proportional to CO₂ + N₂ injection rate which directly affecting solid ‐ gas contact time. Qualitative/quantitative analysis on compositional profiles at each port reveals that the length more than 5.6 m is required to show noticeable recovery rate for NGH production. These outcomes are expected to establish the optimized key process variables for near future field production tests. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1004–1014, 2015     

Modeling of CO2 mass transport across a hollow fiber membrane reactor filled with immobilized enzyme

The enzyme‐based contained liquid membrane reactor to capture CO₂ from the closed spaces is a very complicated process with large numbers of interdependent variables. A theoretical and experimental analysis of facilitated transport of CO₂ across a hollow fiber membrane reactor filled with immobilized carbonic anhydrase (CA) by nanocomposite hydrogel was presented. CO₂ concentration profiles in the feed gas phase and the membrane wall were achieved by numeric simulation. The effects of CO₂ concentration, CA concentration, and flow rate of feed gas on CO₂ removal performance were studied in detail, and the model solution agrees with the experimental data with a maximum deviation of up to 18.7%. Moreover, the effect of CO₂ concentration on the required membrane areas for the same CO₂ removal target (1 kg/day) was also investigated. This could provide real‐world data and scientific basis for future development toward a final efficient CO₂ removal device. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Polyester–Polycarbonate blends. III. Polyesters based on 1,4-cyclohexanedimethanol/terephthalic acid/isophthalic acid

Melt blends of polycarbonate with Kodel, a homopolyester formed from 1,4-cyclohexanedimethanol and terephthalic acid, and with Kodar, a copolyester formed by replacing some of the terephthalic acid with isophthalic acid, were prepared and their transitional behavior were examined by thermal analysis and dynamic mechanical testing. Blends formed with either polyester were found to have a single T_g over the entire compositional range. Single composition-dependent α- and β-relaxation temperatures were also observed for blends made with either polyester at all compositions. From these data it is concluded that both Kodel and Kodar blends with polycarbonate form miscible amorphous phases. The role of ester–carbonate interchange reactions during melt mixing was experimentally examined and found to be unimportant, from which it is concluded that the observed miscible phase formation is due to physical interactions between the blend components.     

Molecular geometry effects and the Gibbs–Helmholtz Constrained equation of state

Differences in molecular size and shape have long been known to cause difficulties the modeling and simulation of fluid mixture behavior and generally manifest themselves as poor predictions of densities and phase equilibrium, often resulting in the need to regress model parameters to experimental data. A predictive approach to molecular geometry within the Gibbs–Helmholtz Constrained (GHC) framework is proposed. The novel aspects of this work include (1) the use of NTP Monte Carlo simulations coupled with center of mass concepts to determine effective molecular diameters for non-spherical molecules, and (2) the use of effective molecular diameters in the GHC equation to predict phase behavior of mixtures with components that have distinct differences in molecular size and shape. Numerical results for a CO₂–alkane, alkane–water and CO₂–alkane–water mixtures show that the proposed approach of combining molecular geometry with the GHC equation provides accurate predictions of liquid densities and two- and three-phase equilibrium.     

CO2 Capture Using Activated Amino Acid Salt Solutions in a Membrane Contactor

An activated solution based on amino acid salt was proposed as a CO₂ absorbent. Piperazine (PZ) was selected as an activating agent and added into the aqueous glycine salt to form the activated solution. A coupling process, which associated the activated solution with a PP hollow fiber membrane contactor, was set up. An experimental and theoretical analysis for CO₂ capture was performed. The performances of CO₂ capture by the coupling process were evaluated using the PZ activated solution and the non-activated glycine salt solution. A numerical model for the simulation of the hollow fiber membrane gas–liquid mass transfer was developed. Typical parameters such as outlet gas phase CO₂ concentration, capture efficiency, and mass transfer coefficient for the activated solution were determined experimentally. The effects of operation temperature and liquid CO₂-loading on mass transfer coefficient and capture efficiency were discussed in this work. Axial and radial concentration profiles of CO₂ in the fiber lumen and mass transfer flux were simulated by the model. Results show that the performances of the PZ activated glycine salt solution are evidently better than that of the non-activated glycine salt solution in the membrane contactor for CO₂ capture. Elevation of the operation temperatures can enhance the overall mass transfer coefficient. The activated solution can maintain higher capture efficiency especially in the case of high CO₂-loadings. The gas phase CO₂ concentration with the activated solution is lower than that with the non-activated solution whether along axial or radial distances in the fiber lumen. The model simulation is validated with experimental data.